EVTV S85kWh Tesla Model S Fullpack Controller Instruction Manual
- June 13, 2024
- EVTV
Table of Contents
S85kWh Tesla Model S Fullpack Controller
Product Information
Product Name: Control Module for Tesla Model S 85kWh Battery
Manufacturer: EVTV Motor Werks
Copyright: 2017 EVTV LLC
Battery Controller Version: 1.3
Date of Release: December 2017
Introduction
The Control Module for Tesla Model S 85kWh Battery is designed
to provide efficient control and management of the battery in your
Tesla Model S vehicle. This module is manufactured by EVTV Motor
Werks, a reputable company in the electric vehicle industry.
Product Usage Instructions
-
Ensure that the Control Module is compatible with your Tesla
Model S 85kWh Battery. -
Refer to the user manual of your Tesla Model S for instructions
on how to locate and access the battery compartment. -
Disconnect the negative terminal of the battery to ensure
safety during installation. -
Carefully install the Control Module in a suitable location
within the battery compartment, following any specific instructions
provided by the manufacturer. -
Once installed, reconnect the negative terminal of the battery
and ensure a secure connection. -
Refer to the user manual or documentation provided with the
Control Module for information on how to connect it to the
vehicle’s electrical system. -
Follow the recommended wiring and connection procedures to
ensure proper functionality. -
If necessary, configure any settings or parameters on the
Control Module according to the instructions provided. -
Test the Control Module by turning on your Tesla Model S and
observing its performance. -
If you encounter any issues or have questions regarding the
installation or usage of the Control Module, refer to the user
manual or contact EVTV Motor Werks for assistance.
It is important to follow all safety guidelines and procedures
provided by Tesla and EVTV Motor Werks when working with the
battery and electrical components of your Tesla Model S. Improper
installation or usage may result in damage to the vehicle or
personal injury.
For more information and updates, you can visit the official
website of EVTV Motor Werks: http://evtv.me
EVTV Motor Werks
Control Module for Tesla Model S 85kWh Battery
Copyright 2017 EVTV LLC
Battery Controller 1.3
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INTRODUCTION
The long established and familiar Solar Industry is about to undergo a
dramatic change in direction due to a “perfect storm” of forces coming
together in the very near future. This perfect storm is the result of three
main factors:
1. Rapidly declining cost of photovoltaics. 2. Growing public awareness of
the necessity for renewable energy 3. Growing need for electrical power during
disaster events 4. Alienation of entrenched grid operator interests 5.
Widespread adoption of electric vehicles .
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Items 1 through 3 are pretty much self evident. But items 4 and 5 are
relatively new factors to the solar industry.
Both home and commercial solar installations should be viewed as a great boon
to the existing grid-utility operators. Maximum production of solar-based
electricity occurs during the day and early afternoon when power demand is at
its greatest due to industry use and the heavy loads imposed by air
conditioning.
By providing power to the grid during these peak times, and using power from
the grid during the night when loads are much lower, these installations offer
an inherent and extreme advantage to grid load management. The partnership
between solar power producers and the entrenched electric power providers
should be a Kumbaya moment with everyone holding hands and moving forward
together toward a much cleaner brighter future.
Unfortunately, an entire cottage industry has sprung up of consultants warning
utility companies of the imminent destruction of their business model by the
selfish and evil proponents of home solar electric power, characterized as
“free riders” in this utiltity industry disaster scenario.
This has quickly evolved completely past net-metering issues to the point that
most utility operators now view ALL home and business solar installations as
“free riders” who require the installation and maintenance of plant of any
other utility customer, but who do not use the normally factored and expected
levels of electricity consumption assumed in their business model. As such,
they posit that non-solar utility customers are forced to “cross subsidize”
those who install, at their own expense, solar power equipment. Simply because
they are not consuming enough utility grid power.
The position has rapidly evolved somehow to not only NOT reimburse these solar
customers for power provided to and used by the grid, but to enact severe
penalties in the rate base for using solar electric at all.
In effect, they have declared war on their own customer base, or that portion
of it that installs any level of photovoltaic electricity generating plant.
Solar installations have for many years been almost entirely based on the
concept of “grid-tie” and has been bolstered both by Federal tax incentives
and net-metering which most states mandate. And so individual homeowners would
provide the grid power during the day when sunlight was plentiful, and
withdraw power from the grid at night, effectively using the grid as a sort of
energy storage device or battery.
The entrenched interests in monopoly utility providers have now turned full
force to persuade politicians and regulators at both Federal and state levels
to revise laws regarding solar installations to preclude this and warn of dire
consequences to “the grid” if they don’t get their way. With the ready
application of heady levels of campaign contributions and these threats of
doom and mayhem ahead, they are finding a willing ear among legislators and
PUC regulators.
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The entire position enacts a kind of self-fulfilling prophecy that we predict
will basically bring “the grid” to its final death throes within 20 years.
They had rather enjoyed a position in the catbird seat as the future
arbitrageur of all economic transactions in all directions in a grid connected
national network of solar installations. They also provided a handy point
providing for easy and ready taxation of electrical power by cities, counties,
and states.
Ironically, this will be forfeited entirely in their myopic and paranoid
vision of their own user base while in the very ACT of paying high premiums to
peaker plant operators for electric power they get from small solar
installations at a fraction of their normal costs for power.
But it is essentially in the nature of entrenched interests facing disruptive
technological advances to make all the wrong moves to survive it. There are
very few AT&Ts willing to morph their landline business into a leading role in
cellular telephone. Most are Eastman Kodak’s who eventually sell their office
furniture for six cents on the dollar.
Ultimately, the key to successful small solar installations is exactly the
same as it is for solar power generally energy storage for use in the dark.
And the concept of using the grid as a storage medium was fatally flawed from
the beginning. They already had their own load management issues and were ill
equipped generally to act as a storage facility for solar power. So while
there were some inherent marginally complimentary interests in peak shaving,
ultimately the grid was always destined to be a very poor battery for energy
storage.
While any number of creative proposals for energy storage have been floated,
there is one practical solution and has ever been one solution the electric
storage battery. Heretofore, the costs of this storage, compared to the
available “free” battery provided by the grid, has led to the overwhelming
installation of grid-tie solar installations with very tiny representation
among offgrid or even modest battery backup installations. A few teleco and
computer server installations that were very sensitive to power losses, and
locations simply not served by the grid, were the only real applications for
battery storage of solar generated electricity. “Off-gridders” were the kookie
fringe element of home solar.
Batteries suffer as a solution in that they are expensive, heavy, take up a
lot of room, require regular maintenance and frequent replacement.
But we believe the future of ALL solar power revolves entirely around the
topic of energy storage and batteries to provide that energy storage. ALL
issues of the future will be battery-centric.
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ADVENT OF THE LITHIUM ION BATTERY
The development of the lithium-ion battery has dramatically changed the
equation, drastically improving some elements of battery storage, while
dramatically worsening other aspects.
Lithium-ion batteries are not precisely “chemical” batteries in the same sense
that lead based technologies are. There is no “state change” in materials as
there is no covalent bonding of elements in a lithium battery. They are based
on the movement and “intercalation” of lithium ions between the anode and
cathode and as a result offer the following advantages:
1. Very high energy density. The weight and volume of a lithium battery is ¼
or less that of a lead based cell of the same storage capacity.
2. Very low maintenance. There are no liquids to add or special cycling
required to equalize or erase memory effects or any of that. There’s really
nothing you can do to a lithium battery in this respect at all.
3. Very long lifetimes. The average Trojan deep-cycle lead acid battery is
rated for 300 full discharge cycles. To prolong life, we basically limit
discharge to 50% SOC. But the life cycle remains a factor and replacements in
5 to 7 years are pretty normal. Lithium cells can be fully discharged to
utilize 80% or more if full capacity and are typically rated at 1500-2500 full
discharge cycles OR MORE. They can be expected to last 10 to 15 years.
There are some serious disadvantages to lithium cells as well however.
1. They are much more expensive, typically 3.5x the cost of similar capacity
Pb based cells.
2. They do not allow overcharging or overdischarging at all, and so need
constant management and monitoring through electronic devices.
3. While they do not give off hydrogen gas or contain toxic lead and
sulphuric acid, they can be quite dangerous. With the increased energy density
comes increased danger of fire and explosion if mishandled. Again, battery
management systems must be competent to fully manage lithium cells.
4. While lithium cells can produce power down to 0F temperatures, they can
not and must not be charged below 32F or 0C or they will be permanently
damaged.
There have been a few other entrants in home solar storage such as Nickel-Iron batteries, nickelmetal hydride batteries, and Aqueon’s sodium aqueous battery, none are likely to displace lithium-ion batteries in the foreseeable future as the ultimate storage solution for solar generated
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electricity. Lacking a significant scientific breakthrough currently unavailable, lithium ion batteries will remain in the lead due to a single factor electric cars.
THE ADVENT OF THE ELECTRIC CAR
Lithium-ion batteries made the concept of a usable electric car viable for the
first time. And similarly, the electric car makes lithium ion batteries a
solution for home solar for the first time in turn.
Because of their immense power requirements, electric vehicles are now the
largest consumers of batteries of all kinds. And similarly Tesla is now the
largest single customer for batteries in the world.
As such, for the foreseeable future ALL advances in battery technology will
show up in this market first. Electric Vehicles have become the whale in the
bathtub and the 800 lb gorilla in the space. Whatever batteries they use,
ultimately home solar will use. And all future battery advances will go
through the electric vehicle industry first and foremost.
Tesla has now sold over 250, 000 Model S and Model X electric vehicles and has
paid reservations in hand for 455,000 Model 3 electric vehicles. ALL other
automotive manufacturers are now in a panic to catch up before their business
model is disrupted as well. But there are over 100,000 Leafs and a similar
number of Chevrolet Volts and Bolts out there as well.
A peculiar seam in the zone has appeared for solar installers rather
immediately. The cars offer inordinately high performance few new owners are
able to handle and the number of wrecked cars resulting is unusually high.
Given the nature of the aluminum bodies of these cars, they can be very
expensive to repair from even minor collisions and are routinely written off
as a total loss by insurers and relegated to salvage yards for parting out.
Except nobody knows what to do with the parts. Perfectly good drive trains,
chargers, and batteries are available in this way, but the undamaged fleet of
cars are mostly still under warranty and these items are very very low failure
even in high mileage cars off warranty. So there is basically no market for
these parts. The case of the batteries is particularly egregious. Warranteed
usually for 10 years and 100,000 miles, or eight years and 100,000 miles,
often the car has 5,000 or 10,000 total miles on it when wrecked. These are
essentially NEW batteries, unlikely to be harmed at all in a collision
(although subject to flood damage).
Because of these warranties, there is NO market for replacement batteries from
salvage for the vehicle fleet. Any battery problems are simply handled by the
manufacturer.
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And there is an inherent mismatch between the batteries used in electric
vehicles and those used in solar storage. It would be UNUSUAL to require 20kW
of power out of a home solar storage battery even for a few minutes. Yet a
Tesla car uses 20kW to idle down the road at 25 mph and can demand as much as
350 kW during rapid acceleration.
Further, an electric car needs a specific range. And at the point where the
battery is “worn out” is considered to be when the cells have deteriorated
sufficiently to offer 80% of their original capacity. You would normally
replace your vehicle battery at that point to regain your original range
capability.
Home solar energy requirements don’t precisely have a range requirement. You
add as much capacity as you want in hours of operation with no sun. It is
entirely stationary and more or less arbitrary.
Better, the levels of power required of the battery are comically trivial
compared to what it endures in a vehicle. A huge house will likely average 7
or 8 kilowatts of power per hour. Peaks of 20kW are almost unlikely. But even
50kW of instantaneous demand would be unnoticeable to a large vehicle battery
which could easily do 100kW continuously and routinely provides 350400kW for
brief periods.
Historically home solar battery installations have also been trivial in
capacity with 10kWh being the norm and 50kWh being considered “very well
backed up.”
A Tesla Model S battery is typically 85kWh. And unlike Pb chemistry batteries,
which are restricted to 50% SOC, some 70 of the 85kWh available in a Tesla
battery could readily be used in a solar application.
At this point, a salvaged Tesla Model S battery is available for typically
$15,000. That’s about $175 per kWh storage.
A Trojan AGM battery designed for solar storage is approximately $500 for a
6v, 375 Ah (2.25kWh). That is over $222 per kWh hour. But wait, there’s more.
Pb batteries are limited to a 50% discharge to maintain cycle life and so the
equivalent pricing is actually $444 per kWh.
Because of the advent and growth of electric automobiles, highly engineered
lithium-ion battery packs are available at LESS than HALF the cost of Pb
chemistry storage of the same capacity. This is an absurdly upside down
situation and an unbelievable “seam in the zone” opportunity for savvy solar
professionals.
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Selfish Solar
Because of this, at EVTV we’ve generated a concept we call various things, but
perhaps most descriptively SELFISH SOLAR. Also internally referred to as
Stupid Solar.
The concept begins with the realization that no home or light industrial solar
installation is truly independent without battery storage. During a series of
recent hurricanes, it became evident that even those HAVING solar power
installations had NO electrical power when the grid went down leaving
millions with no electricity for weeks at a time. The “grid-tied” systems are
actually precluded from generating power even when the sun shines because they
have been engineered with anti-islanding technology purporting to prevent the
electrocution of workmen working on the grid. This dubious theory makes sense
on the face of it, but note that no utility company employee anywhere in the
WORLD, has ever actually even suffered a reportable injury from any home solar
installation ever.
And of course it is trivial to provide a means to disconnect your home from
the grid, either automatically or manually, in the event of a grid outage.
But the requirements have led to an astounding array and breadth of complexity
in the typical home solar equipment area. One model of the SMA Sunny Island
6048 inverter/charger/everything device has over 300 configurable items, some
with as many as 14 different configurations to choose from. It is almost
impossible to find any PROFESSIONAL solar installers who actually are
knowledgeable about this device, generally having memorized about three basic
configurations and simply using those over and over.
For historical reasons, battery back up tends to mean low voltage 12vdc,
24vdc, 36vdc, or most commonly today 48vdc battery systems easily configured
from the traditional 12v or 6v batteries used in cars and golf carts.
But this voltage is far from optimum for inverting to the 240vac split phase
power used by our homes and shop buildings.
It also requires immense cables to carry the necessary current for even modest
levels of electrical power.
Selfish solar refers to a home or shop solar system with a couple of key
characteristics:
1. It adopts the nominal 360vdc voltage (300-400vdc) that has emerged as the
concensus among electric vehicle manufacturers as optimum for automobiles.
2. It is specifically designed to take advantages of economies of scale and
use by repurposing discarded electric vehicle components where able, and most
notably the batteries, to dramatically lower costs of the overall system.
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3. It is selfish. There is no attempt to “share” the output of the system
using the electrical grid. A minimal and almost undetectable grid connection
is maintained, but instead of backing up grid power with batteries, in this
concept, we back up batteries with the grid.
4. It abandons the concept of “weeny” toe-in-the-water solar photovoltaic
systems. From the outset, selfish solar is aimed at fully powering LARGE homes
and shops typical among those who can afford to play this game at all.
5. It specifically avoids multitasking “be everything to everyone” devices in
an attempt to dramatically reduce the complexity, installation issues, and
maintenance by using very “stupid” individual single purpose devices of
dramatically lower cost and complexity.
And so you can readily see this is about reducing costs and making a system
that can be installed and maintained by those with a basic understanding of
electrical systems. And it is most pointedly about building large capacity
systems of 20-50kW capable of providing ALL the power to large homes.
But it is predicated on the assumption of nearly enough a war between utility
grid operators, and their paid for political and legislative minions, and the
home solar operator who seeks independence, control, and to ensure electrical
power in the event of the now all too frequent catastrophic failures of the
grid due to events such as terrorist attacks and more commonly weather events.
With, of course, the ever looming dangers of the Zombie Apocolypse.
This is already happening as utility operators are reducing net metering
payments, increasing various fees for participating, and even making it
illegal to operate a home off grid. Yes, there are American citizens currently
in jail or evicted from their own homes for failing to maintain a grid
connection. This is happening NOW.
Selfish solar advocates a very ordinary grid connection with NO net metering,
special time of day issues, bidirectional meters, or any of that. A very basic
and ideally small 100Amp or at most 200 amp panel and meter duly connected to
the grid and entirely legal in all 50 states.
But we’re going to connect that panel to ONE circuit containing ONE device, an
ordinary electric vehicle battery charger.
A typical onboard charger from any electric car will do about 3kW of power. In
a 24 hour period, this would add a little under 75 kWh of power to a system.
With a 6 kW device, this could conceivably add 150kWh per day. And an ordinary
Tesla onboard charger is 10kW and could easily do 240 kWh per day.
And so in the event of inclement weather reducing your recharge ability for
several days or weeks, you can use the grid to back up your battery powered
home solar installation. But in normal operation, it will use almost zero
electricity and you will pay the minimum monthly fee to be connected to the
grid.
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CHARGER REQUIREMENTS
Any electric vehicle charger can be used that can charge to 300-400vdc from
ordinary 240vac split phase power. It should be of sufficient quality to run
24 hours, but almost all onboard chargers are designed for 8 to 10 hours per
charge anyway.
INVERTER REQUIREMENTS
The inverter will of course produce 240vac split phase power. This is normally
described as L1, L2, Neutral, and earth ground. It consists of two 120vrms
outputs that are 180 degrees out of phase. Most electrical devices work from a
single phase at 120vac. Electric driers, air conditioners, and stoves often
use both phases at 240vac.
The critical issue for the inverter is that it be simple to operate, operate
from 300-400vdc, and have a low voltage cutoff capability to cease operation
when the battery voltage is reduced to a very low state of charge typically
around 300vdc.
The inverter output is fed into the load panels currently in the home,
replacing the normal grid connection to those panels.
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The Tesla Model S Battery Pack
The most common battery pack installed in the Tesla Model S vehicle is a nominal voltage 360vdc and 236 Ah for a total capacity of 85kWh. There are smaller packs of 60kWh, 70kWh, and more recently larger ones of 90kWh and 100kWh, but the 85kWh pack is currently the most common.
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Ironically, the software in the Tesla Battery Management System pretty much
reduces the available energy to about 75.5kWh. The entire battery is contained
in an aluminum “slab” mounted to the underside of the vehicle giving it a very
low center of gravity. This pack weighs 1330 pounds. It is 106 inches long and
62 inches wide but only 6 inches thick.
Internally, it consists of 16 “modules” of nominally 21.6vdc wired in series
for 360v. Each module consists of 444 small battery cells in the 18650 format.
That is 18 mm in diameter and 65 mm long slightly larger than a AA battery
cell.
And so the entire pack contains 7104 of these small cells.
It contains an advanced Battery Management System and each module contains its
own Battery Management subunit. It also contains two contactor relays to
connect the battery to the interface connector as well as high current fuses
to disconnect in the event of malfunction.
This BMS system is capable of balancing all 7104 cells to precisely the same
voltage and can read the voltage of any individual cells and monitors all cell
voltages continuously.
The pack also features a very advanced cooling system that winds through each
module and makes physical contact with each and every one of these 7104 cells.
And the BMS continuously monitors the temperature of each terminal of each
module.
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The pack is typically charged to 4.2v per cell or 400v per pack and is easily
capable of providing up to 1155 amperes of current for 462 kW of power. The
rear drive train of the Model S is typically 350kW while the front drive unit
is generally 170kW in power.
The Tesla Model S car externally provides heating or cooling to the fluid
routed through the pack as necessary.
The pack provides the power through a very unusual heavy-duty blade connector.
There is normally NO power connected to this. Two control connectors, X035 and
X036 provide the electrical interface to the car.
The vehicle provides 12v operating voltage to the battery pack, and
communicates with the pack via Controller Area Network (CAN) messages with the
vehicle commanding the pack to turn on and the pack reporting voltages and
temperatures to the vehicle master control unit and the drive train. In this
way, the battery BMS is commanded by the car to energize and connect the
battery to the vehicle. The BMS closes two internal contactor relays and the
blade connector becomes “live” with the pack voltage available.
Tesla’s battery technology is the heart of their franchise and their very
advanced highly engineered battery packs are considered the best in the world
and the envy of all other vehicle manufacturers, many of which have actually
used Tesla batteries in their cars, including Daimler, Mercedes Benz, and
Toyota.
In this way, a package of 23 cubic feet and 1330 lbs can provide 85kWh of
storage.
This would be the equivalent of 76 of the 6v 375 Ah Trojan Solar batteries
which would weigh 8,664 lbs and occupy 58 cubic feet of volume.
The big question about Tesla batteries revolves around how long they will
actually last. They are warranted for 8 years and 100,000 miles to 80%
capacity. But as the cars were introduced in 2012, almost no one has driven
one to that point. Indeed, extremely few batteries have been replaced at all
and almost all of those that have were due to contactor or fuse failures not
the cells themselves.
A group of Tesla owners based in the United Kingdom have put together a spread
sheet and online system to allow owners to report their range, as reported by
the Tesla Master Control Unit (MCU) in the car, against miles driven, charge
cycles, and calendar time. The results are interesting.
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The concensus seems to be that the trend line of this group reporting with an
impressive number of data elements points to an ultimate lifetime of an
astounding 750,000 km or some 466,000 miles.
Similarly the charge cycle data would imply a lifetime of as many as 2500 full
discharge cycles to a capacity of 80%.
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Battery age is much more complex as people drive their cars at different rates
regarding the number of miles driven per year. So we’re not too sure what
value the final graph might have but it implies again a long service life.
Now understand, their interest is to 80% of original capacity. And that is
important to a car owner in that the range they can expect from the car is an
important variable in car ownership. If the car originally got 275 miles on a
charge, then at 80% it is down to 220 miles.
In solar applications, this is not nearly so critical. Indeed we could START
with the batteries they discard at 80% capacity and do very well indeed.
And so we can see that the advent of electric vehicle batteries is a game
changer for home solar storage. We can now for the first time envision much
larger capacity batteries with much smaller weight and space requirements and
much less expense than ever before known in the industry, by repurposing used
electric vehicle battery packs for solar storage use.
Because of this, we see a coming “inflection point” in solar energy technology
moving toward a much more battery-centric system and more independent solar
installations.
Unfortunately the Tesla Model S pack is not usable as available. The system is
highly integrated with the car and you cannot even access the voltage of the
pack without highly involved CAN message exchanges with the pack. EVTV has
reverse engineered this and can basically simulate
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the car to the pack with a small controller box. This box also allows you to monitor all cell and module voltages and temperatures, and set limits for voltage and temperature. It also provides for precharge of the capacitors in charge controllers and inverters, and two contactor relays to make the connection. These contactors are automatically disconnected if any of the voltages or temperature limits are exceeded, allowing safe operation of this pack.
THE TESLA BATTERY MODULE
The Tesla Battery Pack is a bit unwieldy for home installations at 1330 lbs. Additionally, it is inaccessible without a controller capable of simulating the car to the battery pack.
For this reason, many individuals experimentally have chosen to disassemble the battery pack, and harvest the individual modules. The terminals of the modules themselves are of course live and can be connected to provide voltage and current to any system. And two modules fully charged in series come to 48vdc exactly, which is a common voltage for off-grid solar installations now.
There is an inherent and fatal flaw in this however. And I mean potentially FATAL flaw. The Tesla battery uses a lithium ionic cell with an graphite silicon anode and a cathode made of nickel, cobalt, manganese, and aluminum that is intercalated with lithium. They are termed LiNiCoAlO2 or commonly NCA cells.
These cells provide a very HIGH energy density, quite beyond all other lithium-ion cells in use. This is the secret to Tesla’s long range in their cars. They use very high energy and power density cells.
The downside to that is they are very “hot” in the sense that any damage, overcharge, overdischarge, overtemperature, undertemperature, or other mishap sends them into a thermal meltdown which is “contagious” to contiguous cells and rapidly results in an extreme thermal runaway event. Indeed, a small number of Tesla cars have experienced enormous explosions with horrendously hot fires that are very difficult to put out.
Thankfully, these incidents are very few in number given the number of cars on the road. But it is largely due to a VERY advanced highly engineered system that Tesla has carefully designed and put in place to protect these battery cells.
And so using these modules by connecting the positive and negative terminals together and to a charger and an inverter is a recipe for disaster. In a home, it means ultimately and somewhat inevitably a home burned to the ground.
At EVTV we have built many electric vehicles without any BMS at all and in fact have eschewed the use of battery management systems generally as being too complicated and themselves
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unsafe. But that was with much more benign LiFePo4 cells, with much lower
energy density, and taking into account the many amateur BMS designs our
viewers were inclined to use.
Glomming on a battery BMS designed for electric vehicles, often available
because it was designed by amateurs with little testing and field experience,
is likewise not a good strategy.
The Tesla Model S battery module has a very capable Texas Instrument chip
based Battery Management System module on each battery module. We advocate
using the system Tesla itself designed to monitor and control these modules as
the only means of use offering an acceptable level of safety. But note in ANY
application, these battery modules are a significantly higher level of hazard
than the Pb batteries you may be accustomed to . They are simply not
comparable.
The Tesla Model S battery system consists of 16 individual modules. Each are
685 by 300 by 75mm in dimension and weigh 55.8 pounds. They consist of 444
individual 18650 battery cells with 74 cells in each voltage cell and six of
these voltage cells in series 6S74P.
The battery cells are most likely Panasonic NCR18650BE cells or close equivalent of nominally 3300 mAh capacity and 3.6vdc. These cells are of a nickel cobalt manganese aluminum oxide cathode and a graphite silicon anode.
For an 85kWh Tesla battery, this gives the module a 74 x 3.3Ah or 244 Ah capacity at the nominal voltage of 3.6v for a total power storage capacity of 5270 watt
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hours and a module nominal voltage of 21.6 volts. These modules are designed
to produce up to 1155 amperes of current for brief periods. And so 16 modules
provide 84320 Wh of storage.
The 60kWh Tesla battery uses 21 less cells per module at 53 cells for a total
of 175 Ah or 3780Wh per module and 60480 Wh per pack.
The cathode chemistry of these cells is such that gives off free oxygen at a
fairly low thermal temperature of perhaps 180C very low by lithium battery
standards. Without adequate monitoring, they can easily be driven to thermal
runaway by overcharging or overdischarging and can be explosive. The resulting
fires are extremely hot and since they produce their own oxygen from cathode
materials, extremely difficult to extinguish.
The individual batteries are interconnected by thin plates on top and bottom
with holes at the cell terminals. Small wires are welded from the plates to
the center of the cell terminals. These wires are designed to act as fuses in
the event of the short failure of any particular battery cell.
A series of flat fluid conduits winds between the rows of battery cells. These
are connected to two pipe fittings on the end of the module. In the battery
assembly these fittings are connected to clear tubing from one module to the
next and to some external fittings to allow the circulation of fluid that can
be externally heated or cooled as necessary.
A battery monitoring printed circuit board is mounted on one end of each
module. It measures the voltage of each individual cell and the temperature of
positive and negative module terminals.
A 10 pin molex connector at the top of this module board allows connection to
a daisy chain cable assembly connecting all the modules to a central battery
management system board in the end of the main battery assembly. This main
board operates the contactors in the battery assembly and communicates with
other vehicle components via Controller Area Network CAN bus.
The modules are designed to be charged to a maximum voltage of 4.2 volts per
cell for 25.2 volts per module and it is extremely important that this voltage
never be exceeded.
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The cells are essentially 100%
discharged at a static resting voltage
of
3.0 volts or 18 volts per module.
Under high current loads, this lower
voltage may of course be much less,
but it is important that in a static
condition, 3.00v is essentially fully
discharged. Overdischarge can
similarly cause damage to the cell
and it will not normally be readily
apparent until the next charge cycle,
which can then be catastrophic.
The cells have a fairly flat discharge curve making it difficult to determine state of charge by voltage alone.
It is very important that NO charging of a Tesla Module S battery module be performed at an ambient temperature below freezing – 0C or 32F. Charging at cold temperatures leads to lithium dendrite formation on the anode and eventually failure of the plastic separator in the battery cell. If you need to charge these modules in extremely cold weather, you must make provisions for heated fluid circulation through the modules. Again, EVTV has designed a controller and wiring harness that allows you to connect up to 62 of these modules and set limits on operation based on voltage and temperature reported by the Tesla designed BMS board on each module. It has contactors for precharge and connection and will automatically disconnect if any of the limits you have set for voltage, temperature, or even variance between cells is exceeded. http://store.evtv.me
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EVTV Control Module for Tesla Model S Battery Pack
The Tesla Model S battery pack offers a number of advantages and a few real disadvantages for solar energy storage. The pack provides a very large amount of storage capacity, some 220 ampere-hours at a nominal voltage of 360 vdc. This would be the equivalent of providing over 80 kW of power for an hour. Picture 345 amperes of 240vrms AC power for an hour.
It does so in a remarkably low volume of 23 cubic feet and at a very low
weight of 1330 lbs.
Perhaps the ideal installation would be to remove the 16 individual modules
and install them in custom racks for a total weight of 896 lbs and a more
convenient volume at that. And so we have developed a controller for the
individual modules.
But we think there is an application for the full battery pack. Pack
disassembly is quite a bit of work. There is something to be said for simply
sliding in a pack as received from the salvage yard, adding a second one as
necessary, and replacing them on failure with yet another. This is appealing
as part of the “keep it simple” concept of Selfish Solar.
The pack, however is highly engineered and tightly integrated with the car.
Out of the car, it actually doesn’t allow any electrical connection to the
power in the pack at all, disconnecting the battery pack from the output
terminals entirely.
But a fully featured Battery Management System is contained within, and
despite the basic chemistry of these cells being quite dangerous, Tesla has
done an excellent job of designing a control system for safety.
The EVTV Tesla Model S Battery Pack Controller simulates the car to the
battery pack. It completes all the High Voltage Interlock circuitry necessary
to power the output, provides all the contactor voltages necessary, and
provides the Controller Area Network (CAN) messages necessary to operate the
pack as if it were in the car. It also interpretes the CAN messages FROM
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the pack to gather information on individual cell voltages, currents, state of charge, balance, and more.
Despite the fact that the Tesla battery pack features high current contactor
relays to control access to the pack, the EVTV controller adds two more
allowing YOU to configure your own limits as to voltage, cell balance, and
temperature and quickly disconnect the pack from your system if anything goes
amiss.
It also allows you to easily observe all aspects of the pack operation via a
USB serial port connection. And it can externally control your solar charging
of the battery, or your grid tied charging of the battery.
The controller actually plugs directly into the slotted power terminals of the
pack using a pair of heavy copper buss bars to carry the power to the
contactors.
It also features two mating plugs for the X035 and X026 connectors on the pack
for control signals.
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It provides 12vdc to the pack that is normally available from the automobile.
It does this using an internal lithium 12vdc battery and once connected to the
full pack power, uses a DC-DC converter to recharge this internal battery and
provide power to the Tesla battery or externally through a connector to other
devices. This external connector could also be used to “jump start” the system
in the event of failure or discharge of the internal 12vdc small battery.
Access to CAN traffic is provided via a CAT6 RJ45 connector. And a USB serial
port is provided to allow connection of a laptop with terminal program to
easily configure the battery using simple ASCII text commands and to observe
voltage and current and power activity down to the individual cell level of
each of the 96 internal 3.6vdc cells.
A latching and lit ON/OFF switch allows you to power up the system and red and
green LED indicators show the state of the two internal contactors.
Finally, it provides two PG-21 gland nut ports to run appropriate cabling from
the internal 300 amp contactors to your solar inverter and photovoltaic array.
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INSTALLATION
To install the controller and begin operation:
1. Insert cables connecting controller to the system such as the MPPT Charger
Controller and Inverter inputs through the provided PG21 cable glands provided
in the end of the controller and secure to contactor terminals.
2. Insert High Voltage Interlock shorting pin into the HVIL receptacle of the
power connector on the battery.
3. Insert the controller onto the battery with 1-inch bus bars seated into
the power connector and push down until controller is firmly seated in power
connector.
4. Press the latching ON/OFF switch on the front of the controller.
After a few seconds, the RED will light indicating that power has been applied
to the internal battery contactors and the negative contactor of the
controller has been energized initiating the precharge sequence.
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After the precharge delay has completed, the green LED will light indicating
the positive contactor has energized. You should now have power to your system
from the battery.
You may plug a laptop computer into the provided USB port to access the data
display and configuration menus to set up your battery for operation.
CONTROLLER SOFTWARE
The central function of the controller is to allow access to the battery. But
it is also very important to monitor battery voltages, temperatures, and cell
variance and immediately disconnect the battery from the system if it is in
danger of being overcharged, overdischarged, or if there is some internal
failure of any of the 7000 cells making up the battery pack.
The controller receives a variety of information from the battery’s internal
BMS over the CAN network bus. And it provides access to this information in
ASCII text form via the USB port.
Another important aspect of the controller’s function is that it allows the
user to configure the LIMITS defining voltages and temperatures that will
result in an automatic shutdown of the battery pack and a disconnect from
external systems.
The main access is via the USB port. This requires the use of an ASCII
terminal program from any personal computer. As this is a serial USB
connection, it operates at a speed of 115,200 bits per second, 8 data bits, no
parity, and 1 stop bit (8N1).
It might be more visually pleasing if the ASCII terminal recognizes form feed
control characters.
The controller would normally operate without any supervision. But the user
can access this software at any time by simply plugging into the USB port with
a laptop. Menus can be navigated and values entered but all entries must be
terminated with a carriage return or line feed.
On connecting to the port, the MAIN SCREEN should appear immediately.
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The title bar lists the software version and the run time since the last power
cycle in days, hours, and minutes and seconds.
It also displays the serial number of the battery pack and the number of
Odometer miles on it when it ceased operating in the car essentially the
number of miles on the pack at salvage.
Several single character commands are available from this screen. A “t”
character will toggle the contactors from off to on or from on to off..
There are four menus numbered 0 through 3 and each may be accessed by simply
entering the number.
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Below the menu, the state of the Tesla battery pack internal contactors, the controller negative contactor, the controller positive contactor, and the CHARGE ENABLE output are all displayed.
The CHARGE ENABLE output is a 12v power supply with switched ground return. When off, the ground side is floating. When ON this is connected to ground. And so if this output, which is available via a two pin connector on the front of the device, is set to ON, it could light an LED, energize a relay, or take other action to control external charging equipment such as a photovoltaic array or an ordinary battery charger.
The next line displays current operating information such as battery voltage, current either in (charging) or out (shown as negative for discharging), instantaneous power, and the average temperature of all 32 terminals within the pack. It also displays the voltage of the controller 12v bootstrap battery or the output of the high voltage to 12vdc DC-DC converter within the controller used to power the contactors and control circuitry.
Beneath that we display ampere hours consumed from full, the state of charge SOC calculated by the controller, and the SOC reported by the Tesla internal BMS.
Why would these be different?
The Tesla battery pack generates the SOC value displayed on the instrument panel in the car. This can either be displayed as a percentage or miles remaining in the car. This value represents the state of charge of the batteries but is skewed by a number of factors intended to protect the battery. The result is about a 75.5kWh availability.
You also can set limits on voltage and current and so forth via the LIMITS screen described later. One of those limits is the total ampere-hours you will use from the pack, and this is obtained experimentally by using various charge cutoff and MAXCELL voltages and various MINCELL voltages as you like. And so this main SOC is a function of the portion of the battery you actually designate for use in your solar application. You might set charge cutoff to 4.1 or even 4.0 volts to extend the life of your battery and similarly the discharge cutoff or minimum voltage to 3.10. In doing so, if you will measure the total ampere-hours consumed from full charge to full discharge and enter that value, the controller will accumulate actual amp-hour consumption and calculate SOC based on your entered total capacity.
The line beneath shows the total kWh contained in the pack and the total kWh necessary to fully charge the battery. This is based on the full capacity calculated by the Tesla BMS.
Below this is a summary of individual cell data showing the highest cell voltage, the lowest cell voltage and the average cell voltage. It also shows what the Tesla BMS calculates as the SOC of the cell with the least capacity, the deviation, and the alarm count.
Deviation is the voltage between the AVERAGE cell voltage and the highest or lowest whichever is greater. You set a value in LIMITS for the ALLOWABLE deviation and if it is exceeded the controller will disconnect the pack. This is for the event where one cell goes bad and this is usually a very effective means of detecting this early on.
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The alarm count is the number of reported voltages that would normally trigger
a shutdown of the pack. Unfortunately, CAN communications being what it is,
occasionally spurious messages are received indicating a zero voltage of a
cell that is perfectly operational. If we disabled the pack based on this
spurious report, you would have constant outages based on the anomalies of
electronic circuitry.
In the event of an actual cell failure, the CAN message traffic would report
this repeatedly a number of times per second and quite consistently. In a very
few seconds the number of alarms would accumulate and the system would indeed
shut down.
In LIMITS you can set the “sensitivity” of these alarms so that it will not
trigger a shutdown until a certain number of these reports are received. This
sensitivity level is between 1 and 255 and with higher numbers it is less
sensitive.
Beneath that is a history section. The first line shows the total kilowatt
hours that have EVER been put into the battery or taken out of the battery.
This is kind of a running odometer indicating battery age and use.
The next line shows the maximum and minimum pack voltages since the system was
last power cycled (turned on).
And finally it shows the peak charge and discharge current and power for this
session.
In this way, the main screen provides an instant overview of all operating
parameters related to battery energy storage.
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INDIVIDUAL CELL VOLTAGES SCREEN.
The next program screen provides a detailed view of the voltage of each of the
16 modules within the pack and each cell within those modules.
This is purely informational and there is really no action to take here.
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MODULE VIEW SCREEN
Similarly, entering a 2 will call up the MODULE VIEW SCREEN. Again this screen
is purely informational and shows the voltages of each of 16 internal battery
modules, but also the positive and negative terminal temperature of each
module.
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LIMITS VIEW SCREEN
Similarly, entering a 3 will bring up the Limits View screen. This screen is
actually the most important in the program and provides users the access to
actually set the limits of the battery operation.
The upper part of the screen repeats some operational data. But the lower half
lists a series of variables that can be modified by entering the value name
and a new numeric value.
A discussion of each pack limit follows.
MAXCELL = 4.250
MAXCELL establishes the upper limit on voltage of ANY cell in the pack. This
is to prevent overcharging which can permanently damage cells. Any cell that
REACHES this voltage will trigger an alarm that will immediately cause both
contactors to open and the system to signal the battery pack to disengage the
internal contactors as well.
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To enter a new value, simply enter MAXCELL=4.20 for example followed by a
carriage return or line feed, and you will see this value change instantly on
the screen.
MINCELL = 3.000
MINCELL establishes the lower limit on voltage of ANY cell in the pack. This
is to prevent overdischarge of the pack. ANY cell whose voltage falls to this
level will trigger the alarm and cause an immediate disconnect and shutdown of
the pack.
MAXAMPS = 80A
The Tesla Battery Pack actually contains a fuse internal to the pack but
accessible via a small panel on the far end of the pack from the controller.
This is a Ferraz Shawmut style fuse that reacts based on both current and time
and so won’t blow from spurious spikes but based at a particular current for a
particular time and a curve based on those values. In effect, quite a bit of
damage can be done while waiting for this fuse to blow.
MAXAMPS operates a bit more quickly. If this amperage is exceeded, this will
be read as a voltalarm and will trigger pack shutdown based on the sensitivity
you set. In this way, it acts as another fuse you can adjust for both current
and sensitivity.
MAXTEMP/MINTEMP
Maxtemp and mintemp operate similarly and if any module terminal temperature
exceeds maxtemp, the pack will shutdown Similarly with mintemp.
It should be noted that it is perfectly permissiable to operate the pack down
to temperatuers as low as -20C to produce power. But any effort to charge
cells with a temperature below 0C or 32F (freezing) will result in lithium
plating on the surface of the anode and potentially dendrites penetrating the
insulating barrier within the cell. This could cause catastrophic failure.
The pack does have two ports to circulate ethylene glycol to either cool or
heat the pack. In normal operation, it is very unlikely that the current flows
of a solar installation would cause need for battery cooling. But you may need
to use this system to warm it. If the battery is stored in a covered area,
usually a space heater is sufficient. Temperatures can be readily observed in
the MODULE VIEW screen.
CELLDEV=0.250
While rare, battery cells do fail. In the event of the failure of any particular cell in the pack, it is unlikely that the overall pack voltage or current or temperature will immediately be affected very much. But if left unattended, this could eventually become catastrophic.
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It would likely first show up as a variance of the damaged cell’s voltage when compared to other cells in the pack. CELLDEV allows you to set the limit of how much a cell can vary from the AVERAGE cell voltage before triggering a shutdown of the system and disconnect.
PRECHARGE=12.5 seconds.
When the internal BMS activates the contactors inside the pack, the controller
begins to sequence the external contactors. The battery pack would typically
be connected to an inverter, an MPPT charge controller and other devices.
These devices typically have large values of input or output capacitance.
If we simply energize both contactors, this will connect the 360 vdc battery
directly to an empty capacitor. This causes a very brief, but potentially
catastrophic surge in inrush current into the capacitor as it charges to the
battery voltage. This current spike can easily reach values of 10,000 amperes
or more for very brief periods. The time is so brief it would go largely
undetected, but it has the potential to blow the capacitors rendering the
equipment damaged and inoperable. More frequently, it wil cause the contacts
of the contactor to weld to each other. In this event, there is no way to
disconnect the battery.
To prevent this, the system uses a precharge algorithm. The negative contactor
is closed, but the positive contactor is left open for a defined period of
time. A 500 ohm 50 watt resistor is connected across the terminals of the
positive contactor. And so when the negative contactor closes, this completes
the circuit through the resistor thus charging the capacitors. But the
resistor limits the current to something less than one ampere, a harmless
amount. Within just a few seconds, the capacitors charge to the battery
voltage and at that point, there is no danger of inrush current spikes. The
voltage charge within the capacitors will prevent this.
And so the positive contactor can be safely closed, bypassing the precharge
resistor and connecting the pack to the equipment for full operation.
The amount of time this precharge function takes is a function of the number
of capacitors in the system and their size. And so you can vary this
“precharge time” with this value.
It is generally better to err on the side of too long a precharge rather than
too brief.
CAPACITY=230
The controller receives instantaneous current information from the battery
pack via CAN. We accrue this current level with regards to time to determine
ampere-hours into and out of the pack. We can then use this to calculate a
percentage state of charge independently. The Tesla
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BMS also sends state of charge information but it tends to be modified or
weighted for display on the car instrument screen.
For this reason, we display both SOC and TeslaSOC on the main screen. The
internally calculated SOC requires the true capacity of the battery. You enter
it here for that calculation. We have found that 230Ah seems to be optimal.
AMPHOURS=-16.899
As described, we actually calculate the amperehours discharged (-) from the
pack and charged (+) into it over time by accruing instantaneous current
measurements every few milliseconds. For various reasons, it is occasionally
interesting to zero this value or set it to specific values in order to
observe changes. This is really a remnant of testing we decided to leave in.
Normally you will not need to do anything with this. But you can set it to
zero with the pack fully charged to calibrate your system.
There is also a hidden function to synchronize this value to the reported SOC
from the Tesla BMS. Enter an “a” character on the main screen to synch our
calculated state of charge to the state of charge reported by the Tesla BMS.
SENSITIVITY = 125
The central function of the controller is not precisely to make the Tesla
Model S battery work, but rather to disconnect it and prevent fire or
explosion if anything goes wrong.
And so if any cell exceeds MAXCELL or any cell falls below MINCELL or any
terminal exceeds MAXTEMP or any terminal falls below MINTEMP or even if any
cell falls out of the CELLDEV range from the average of all cells, the
controller will open both contactors and command the Tesla battery pack to
open both of its contactors as well, isolating the battery from any further
charge or discharge activity.
But all of this information depends on CAN message traffic from the Tesla
Battery Management System and due to voltage or current fluxuations and noise
on the line occasional glitches are quite normal in the reported values.
In the example of a cell deviating from normal by more than CELLDEV, for
example, a single message indicating a single cell voltage of zero would
immediately shut down the pack even though there really isn’t anything wrong
with the cell.
In the event of an actual deviation, we would receive the same message 10 or
15 times per second.
Sensitivity sets the number of reported errors allowed before shutting down the pack. And so in the event of a simple communications error, it would be ignored. In the event of an actual voltage
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or temperature deviation, the message would be repeated several times per
second. And so the condition would be allowed but only for a few seconds. This
is an 8 bit integer and so values from zero to 254 are accepted. At 125, a
cell exceeding the MAXCELL voltage for example, would only have to exceed it
for five or six seconds before tripping the actual alarm and causing shutdown.
But spurious voltage readings and stepped on CAN frames won’t set it off. And
so higher numbers decrease the “sensitivity” of the system to variations, and
lower numbers increase sensitivity.
LOGINTERVAL = 1
The controller features an electrically erasable programmable read-only memory
(EEPROM) chip of some 256 kbytes. We use about 100 bytes of that to save your
configuration data so if you shut the system down and then later bring it up,
you don’t’ have to re-enter all of the LIMITS data again.
This memory persists even with power removed and is available each time the
power is applied.
These chips are not very expensive and so there really aren’t any 100 byte
chips available and 256k is pretty minimal, but it is a terrible waste of
space.
We can log the day, hour, minute, voltage, current, and state of charge of the
system periodically to produce a record for testing purposes. You can use this
to generate Microsoft Excel spreadsheets and graphs.
LOGINTERVAL sets the period in minutes between log events. The memory is
sufficiently large that you can log 13 days of activity logging the values
each minute.
Obviously, a log interval of 5 minutes then would provide sufficient log space
for a couple of months of activity.
There are several “hidden” commands to access this logging. “L” causes the
system to display a text stream with one line for each log entry in easily
readable form. Entering a lower case “l” causes the same listing in comma
separated form. And so you can open a text capture buffer in your terminal
program, enter “l” and capture this listing for later import into a
spreadsheet program to make graphs of your solar charging and discharging
activity.
Entering “E” erases the log and resumes logging from the beginning. The number
of each memory “page” will be displayed as it is erased.
Entering “0” (zero) will return you to the main screen.
CUTOFF and RESUME
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In normal charging the pack, we do not really want to shut it down entirely
when we reach full charge for example. Exceeding MAXCELL, for example, will
prevent overcharge by disconnecting all the contactors, but this then requires
YOU to come investigage the problem and manually restart the system.
The controller features a CHARGENABLE output on a two-pin connector with a
constant 12v on pin 1 and a switched ground on pin 2. This can be used to
control external relays, contactors, or signal other equipment.
Whin pin 2 is switched to ground, the circuit is completed for the 12v and the
external relay or contactor would be energized, causing the charger or perhaps
the MPPT solar charge control to be enabled.
When we want charging to stop, the ground on pin 2 is switched off and the
external relay would disengage, stopping charging.
CUTOFF sets the individual cell voltage at which this CHARGENABLE output is
disabled. Once ANY cell reaches this voltage, pin 2 is removed from ground and
this should stop the external charging activity.
No further charging should occur.
Once the system has used energy from the pack, the voltage of all cells should
decrease. RESUME sets the individual cell voltage at which the CHARGENABLE
output is turned back on, RESUMING the charge activity.
We would normally set MAXCELL to something in the area of 4.2v and so CUTOFF
would be set for something slightly lower than that, perhaps 4.15v.
RESUME would be set to something lower than that, perhaps 3.90v.
In this way, the MPPT charge controller or EV Charger connected to the grid
could be activated and deactivated to maintain the battery near the top of the
charge without overcharging and reaching MAXCELL.
When charging ceases, the voltage of all cells will relax or decrease slightly
simply because the charge current has been removed. Having a reasonable gap
between CUTOFF and RESUME avoids hysteresis of constantly cycling the external
charger.
ACCHARGE
As described, a CHARGENABLE output is provided as a switched ground to control a relay that will in turn control the charging of your battery from a photovoltaic array. But we did mention charging from an ordinary EV charger that receives 120vac or 240vac from the grid and charges the pack to 400vdc.
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Almost all EV chargers of Chinese manufacture use a CAN control protocol
developed for the TCCH / ELCON brand chargers. This protocol has become
ubiquitous among all the Chinese chargers.
The controller features an external CAN port that can be connected to these
chargers. It will control the start, operation, and termination of the charge
cycle with these chargers via CAN. It will use the same CUTOFF voltage value
as the photovoltaic array. But we do need to specify a current level for these
chargers as well. ACCHARGE allows you to enter a current level for use with AC
chargers controlled via the CAN port.
OPTIONAL LCD DISPLAY
Ultimately, the Tesla 85kWh Battery Pack and EVTV Controller are just a
storage battery. The design and concept is to have a battery that protects
itself AUTOMATICALLY from every extreme of overcharge, overdischarge,
temperature and the potential for a single cell failure to initiate a failure.
The entire point is you don’t have to be there at all and if it does its job,
there’s nothing to see.
You can easily perform the initial configuration and make minor adjustments in
the first few days of operation using any laptop with the simplest ASCII
terminal program. Thereafter, it should just run. If there is an anomaly,
simply reset and restart with the ON/OFF switch and that will generally take
care of the matter.
In the event you actually DO have a problem, the included software will let
you quickly determine the nature of the fault.
That said, Andromeda Interfaces makes a very nice 7-inch touchscreen LCD
display unit titled the Electric Vehicle Interface Control or EVIC and one
variant of this display is specifically to display data from Battery
Management Systems.
The Tesla Battery Pack Controller software is already configured to support
this display interface via the auxiliary RJ-45 CAN port. And we offer this
display as an optional add-on to the pack controller.
The display comes with a cable to connect to the RJ-45 port and derives both
12v power and CAN connections through the port. It will come up anytime the
battery pack ON/OFF switch is set to ON.
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This display is not as
comprehensive as the ASCII connection via USB, but provides basic information
about battery operation allowing you to tell at a glance the current voltage
and state of charge
The upper left of the screen provides temperature information showing the
maximum temperature reported by the 32 sensors in the pack, and the minimum
temperature reported. You can press this section of the screen to alternate
between Centigrade and Fahrenheit temperature scales.
A battery is displayed center screen. To the left of this is the current
battery state of charge displayed as percent full. You can press this number
to change the SOC to ampere-hours. Unlike the ASCII terminal display of
ampere-hours, this shows the number of ampere-hours REMAINING for use in the
battery. Again it is based on the capacity you configured in the pack limits
configuration and the calculated amphours. The SOC is likewise based on the
capacity entered which is further derived from the charge cutoff voltage you
select and your minimum cell voltage allowed.
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To the right of the battery icon is the current voltage of the battery pack.
This will of course vary with state of charge.
On the right side of the screen the interface displays the cell voltage of the
highest voltage cell and the lowest voltage cell. This gives you a good idea
as to the spread of voltages in the pack currently.
The bottom of the screen provides two progress bars for current showing
charging current at the bottom and discharge current above.
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GRID-TIE CHARGER
As described earlier, the vast majority of residential solar installations to date have been grid-tied with no battery backup and typically use high voltage photovoltaic arrays of 400-600vdc.
A very few have gone to the expense of “battery backup”. And very very few of those have found this was a good investment. Almost all used lead acid Pb chemistry cells and through general disuse, often have failed without attention. So that on the event of an actual power outage, they learn that the “backup” system doesn’t work or only works for a short period.
The selfish solar concept rather turns this situation around and it requires a bit different way of conceptualizing a house power system. Picture a battery powered house. And generally we recharge the batteries using photovoltaic arrays that during daylight hours provide sufficient output to operate the home and fully recharge the battery. At night or during periods of inclement weather, power is withdrawn from the batteries.
Using EV batteries offers the advantage that they feature a voltage range quite compatible with the grid-tied photovoltaic arrays of 400-600vdc. You can literally connect these directly to the batteries without any MPPT or conversion and they will work fine.
But there is an inherent problem in sizing the components of a battery powered home. Sunlight varies.
Obviously, weather events vary the amount of sunlight. A few days of rain can dramatically reduce your array output, though most people are surprised to learn they still produce a little bit of power from the incident light even on stormy days.
But the irradiance of the sun also varies across the year. Below is a depiction of solar irradiance by month for our area just south of St. Louis Missouri, as calculated by the National Renewable Energy Laboratory.
This calculation is based on the amount of solar irradiance falling on one square meter of surface throughout the day. If you have a 20% efficient panel, and have 1000 watts (the standard assumption) falling on one meter of it, you would derive 200 watts. If you had sufficient area, in this case five square meters, you would produce 1kw of power.
But the sun shines most directly on the panel at solar noon. And the 1000 watts falling on that square meter will be less at 11:00 AM and again less at 1:00PM. And indeed it varies throughout the day from dawn to dusk.
If you summed ALL the power produced through the day, you could derive the solar irradiance figure for a 1 kw array really as the number of hours of that much power across the day.
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As you can see from the diagram, in our area that would be 6.51 kWh during the
month of June. And indeed, June features the longest day of the year, the
Summer Solstice in the northern hemisphere, usually about June 21 or 22nd.
As seen on the graph, December features the lowest output at 2.2kWh of
electricity from exactly the same photovoltaic equipment. And indeed, December
features the shortest day of the year, the Winter Solstice in the northern
hemisphere, usually about December 21 or 22nd.
The problem is the ratio. This variation is much larger than most realize. In
our area, we produce about THREE TIMES as much electricity in June as we do in
December. More to our problem here, in December we produce about 1/3 the
electricity we do in June.
And so by season and by weather, it can be difficult to predict how much solar
electricity you will produce. One of the reasons we picture using large
salvaged electric vehicle batteries is with large battery storage of 75 or 150
kWh, we can more effectively buffer these variations.
But outliers can disrupt our power. How about snowfall and overcast skies for
a week or 10 days?
We need to make provisions for supplementing the solar power used to power our
homes in the event of unseasonable weather and particularly during the low
power season.
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A diesel or natural gas generator would be a good choice in areas not served by the grid.
Most would be surprised to learn that in some areas served by a utility grid, it can actually be ILLEGAL to disconnect from it. This is kind of a bald grab for cash by your local government, but you will find without surprise that the areas with the highest city, county and state TAXES on electricity are the MOST likely to have such legal requirements for residential dwellings. Probably just coincidence.
But in our area the basic charge for electric service is about $15 per month plus three or four dollars in taxes. Robbery to be sure, but in a way, small price to pay.
We can basically disappear under the legal and utility company radar by paying it and having a connection to the grid. But in our case, we are only going to have one electrical device connected to the entrance panel, and that is an ordinary onboard EV charger.
Electric vehicles charge from roadside or home “chargers” that are not really chargers at all. They are properly termed Electric Vehicle Service Equipment or EVSE and all they actually do is switch 240vac grid power to the car. Inside the car is the actual onboard charger that converts 240vac into the necessary DC output voltage for battery charging.
These are typically 3 to 5 kw AC/DC converters programmed to charge the battery properly. Unfortunately, they are often liquid cooled, which complicates their use for our purposes.
3kw does not sound like much, but these devices are designed for 6 to 10 hours of operation per day for years at a time. And 3.3 kw output for 24 hours is about 75kWh. This happens to be the total capacity of a Tesla Model S full battery pack and about 2.5 times the average daily household use of electricity in residences in America.
So you could run INDEFINITELY on the grid for snowstorms of months using a single 3.3kw charger. And larger chargers are available. And it would be perfectly suitable to have two of them if necessary to double the output.
You can even limit supplemental charging to night hours when in many areas local utility rates on Time of Day service connections plummet.
In this way, we rather reverse the scenario. Instead of using battery power to back up the grid, we use grid power to back up the battery. And for most of the year we don’t use ANY grid power at all, while still enjoying the advantage of grid connection in the event of poor weather or if we are slightly misized for December and January.
Tesla has a very capable 10kW charger that would be overkill for this. But it very definitely requires liquid cooling and so a heat exchanger, pump, overflow container, and hosing would be required just to cool it.
Most DIY electric car builders have opted for very inexpensive Chinese air cooled chargers. These are simple to operate, require no liquid cooling, and are inexpensive. Due to an oddity in China,
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almost all have adopted the Tiecheng Information Technology Company Lt.d TCCH
charger protocol. This is a very simple CAN protocol to control the charge
voltage and current of a battery charger, and reply with the actual current
and voltage of the moment.
We have included code in the Tesla Battery Pack Controller to control this
charger using the same CAN bus output available to the EVIC display. And they
can coexist very well on the same bus.
The latest TCCH HK-series charger is a marvel at 6.6kW output, air cooled,
quite small, and less than $2000 in all cases. It’s also surprisingly cool and
quiet despite two fans.
As always, this engenders some variables to allow you to set just when the
charging begins and ends and at what rate. These appear on the PACK LIMITS
configuration screen.
GRIDCHARGE. This allows you to set what current level is used for charging.
Typically 0 to 30 amps.
GRIDSTARTSOC. This is the State of Charge Level at which charging begins. If
set to 20 then the CAN messages would cause the charger to turn on when the
state of charge (SOC) level displayed on the main menu falls to 20%.
GRIDENDSOC. This is the state of charge level at which charging ends. You
might not WANT to charge to full using grid to leave room for some solar
additions to the pack for example. If you set GRIDSTARTSOC and GRIDENDSOC to
20 and 60 for example, it would begin charging when the SOC fell to 20% and
would terminate when it was charged to 60% .
Note that in any event, the charger will not charge past the CUTOFF value also
set x 96 cells. So if you have cutoff set to 4.00v it would charge to and hold
384vdc and would taper off the current to prevent any rise above that level.
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Battery Controller 1.3
GRID CHARGING WITH OPTIONAL REALTIME CLOCK
December 2017
We do of course advocate selfish solar and avoiding interacting with the grid.
Long term, we think they are not your friend. But we have already had numerous
requests from those seeking to use batteries as a peak shaving implement.
This requires some knowledge of what specific time of day it is in the local
area. We have developed an optional GPS based real time clock module that
receives satellite navigation data and puts it out over CAN bus.
Because the GPS system inherently provides a very accurate real time clock, we
can then easily put the year, month, day, hour minute and second on the CAN
bus and we have made additions to the controller software to take advantage of
this.
Currently, the system will allow two new variables for GRID Charge using a CAN
controlled charger to use the AC voltage from the grid to charge the battery.
STARTHOUR and STOPHOUR. These configuration variables allow you to further
limit when your grid tied charger is commanded to charge your battery pack.
The hours are simple integers between 0 and 24 representing Universal
Coordinated Time (UTC) start and stop hours.
GRIDSTARTSOC and GRIDENDSOC remain in effect, but charging will actually only
occur between the two hour endpoints.
One viewer actually has a situation with a special EV rate from the utility
company where they can purchase grid power between 11 PM and 6 AM at 1.5 cents
per kWh and sell it BACK to the utility between 6 AM and 11 PM at 15 cents per
kWh. Good work if you can get it.
This peak shaving concept is already causing controversy in Germany and we
expect this opportunity to quickly be addressed by the utility companies here
in the U.S. very shortly, and NOT to the advantage of the customer base.
But various anomalies can be foreseen and adding a real time clock to the
system is easily enough done. If you were in the Central Standard Time time
zone in the U.S., for example, 11:00 PM would corresponds to 05:00 UTC (-6
hours). And 6:00 AM would correspond to 12:00 UTC. So you would simply set
STARTHOUR to 5 and STOPHOUR to 12 .
There is no problem bridging the midnight transition. You could just as easily
enter 23 for start and 6 for stop if you indeed DID live in England where UTC
is the local time.
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local time. The optional GPS CAN module simply plugs into the RJ45 CAN port
and derives its power from pins 1 and 8 of that port while transmitting CAN on
pins 4 and 5 just like the optional display.
Indeed, using an ordinary CAT5 or CAT6 patch panel, you can use both the CAN
GPS and the display at the same time, along with as many CAN controlled
chargers as you like.
SECRET COMMANDS
There are some “undocumented” commands that we are hereinwith “documenting” so
you might say they are just “stray” commands with ambiguous purpose.
These are single stroke commands usually devised to “cheat” the system and
manually override various functions for the purpose of testing or
troubleshooting.
A/a.
The Tesla BMS reports a couple of state of charge values which are dutifully
reported on screen zero, the main screen. But of course, you don’t have to
fully charge the battery to use it. And you
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December 2017
do not have to fully discharge it to cut it off. You can set much more
conservative limits, and indeed we do, and indeed we recommend you do as well.
You accomplish this of course by setting a lower CUTOFF and MINVOLTS values.
But you can also enter a CAPACITY in AMP hours. This is a bit involved but
simply charge the battery until it is just below your MAXVOLTS value. At that
point, enter a Z or z command. This ZEROS a calculated Ampere-Hour value
displayed on screen as AH.
Discharge the battery to just above your MINVOLTS cutoff and NOTE the AH value
on the screen at that point. Enter this as a positive whole number in your
CAPACITY variable. Charging to YOUR cutoff point brings you back to zero
AMPHOURS. This is fully charged. But Tesla reports only 94% SOC. But YOUR SOC
shows 100%
And similarly it shows 0% just before you reach MINVOLTS on the discharge
side, even though the Tesla BMS reports 14% remaining. You have established
your own SOC% based on YOUR criteria for stopping charging or for
disconnecting the battery.
A/a actually revises your current amphour used to match the Tesla reported
SOC. So if Tesla shows 80% SOC, the system will calculate the number of AH
that would be used from your CAPACITY to make SOC match the Tesla BMS SOC.
You will never need to do this. We do it and by experimenting with this, we
can make the SOC and the Tesla SOC match at top and bottom and all the way
through. When you do this, you have to change CAPACITY a number of times to
keep all this in line. Eventually you can learn the real ampere-hour capacity
of your battery.
So you can readily see you will never really NEED to use A/a commands to match
SOC to Tesla BMS SOC. But you can.
T/t.
The T or Toggle command is used to turn OFF all contactors or put the
controller through the
normal initiation cycle to close the internal contactors and perform the
external precharge and contactor closure.
Why?
Opening ALL contactors has an obvious utility. But in actual practice, the “toggle” command has another purpose. The Tesla internal precharge is a timing window based on the capacitance of the circuit to be energized. A voltage is applied through a precharge resistor and the ramp up has to fall within a critical timing window or the precharge is aborted. You will see this sequence as the NEGATIVE CONTACTOR (RED LED) lights and the Tesla BMS is signaled to begin the initiation procedure.
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IF it times out withoout closure, we are kind of left stranded. But this is
normally because insufficient voltage has built up in the precharge capacitor
Often you can recover this by hitting a
t to disconnect and immediately toggling it AGAIN to initiate the sequence.
What this does, is allow the Tesla BMS to charge a capacitor that already has
some voltage stored within. And this shortens the charge timing measurement.
So if your RED led flashes but does NOT stay on, you probably failed internal
precharge. And the easiest way to get past this is to hit
T twice in succession.
Z/z. As mentioned, Z zeroes the current AH calculation. It should really only
be used to set the top
of your SOC when you reach cutoff on a charging session. And you really only
need to do that once.
G/g. G is for GRIDCHARGE and we used this for troubleshooting and testing. IT
simply manually
toggles the AC Grid charger on and off. Normally this charger comes on at a
minimum SOC and goes off at a higher SOC you set wtih the GRIDSTOPSOC value.
It will also taper charge to your CUTOFF value. But you can also use the
optional GPS CAN device to provide a real time clock and only allow such
charging between a start hour and a stop hour, to take advantage of off-peak
utility rates.
And so GRID charging becomes quite complex with times, voltages, and SOC’s all
forming a bit of a
matrix. To test this, we needed a way to manually override. And so G/g simply
toggles the
control bit for grid charging. Note that if you are outside of the time window
and have a real time
clock connected, the G will not actually enable charging. But if you are above
the start SOC
without a clock, or during clock allowed charging hours it will. In this way,
we could test our clock routines as well as CUTOFF and SOC values by toggling
it on when it would not normaly be on.
P/p. Postiive contactor. P closes it and p opens it.
N/n. Negative contactor N closes, n opens.
E/e. This command is used to erase the EEPROM data log of activiity. e simply
resets the system
where it begins writing at the first entry and continues from there.
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Battery Controller 1.3
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E actually writes zeros into ALL the entries of the EEPROM used for logging.
Then resets to
begin writing at entry 1.
C/c. Again a manual override. C turns the CHARGENABLE output on providing a
switched ground and 12 volts to enable external contactors. c turns it off.
R/r. Resets all voltage and temperature data buffers and clears them. The
Tesla BMS should
provide sufficient CAN messages to refill all these within a second or two.
Used for testing.
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