# Use of 6S and 12S Tesla Modules



## AEM (Sep 12, 2014)

I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.


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## Roy Von Rogers (Mar 21, 2009)

AEM said:


> I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.



Do not use the Tesla modules unless you use all the original electronics to run them.

See www.evtv.me for more information.

Roy


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## AEM (Sep 12, 2014)

Well yes I don't think it would be a good idea to run the Modules without the electronics to protect them.


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## SWF (Nov 23, 2007)

AEM said:


> I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.


Mixing 6s and 12s modules in a series string would not be ideal. Since the 6s configuration has 74 cells in parallel and the 12s configuration has 37 cells in parallel, when the cells in the 12s modules are discharged to zero, the cells in the 6s modules would still have half their capacity remaining. You would be better off building your system to use either all 6s or 12s modules.

And yes, you should definitely use the appropriate BMS to monitor the modules, however most folks using these modules are not using the original Tesla slave BMS boards that are on each module. They are using the built-in cell taps on the modules that can be used to connect a separate BMS.


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## onegreenev (May 18, 2012)

EVTV likes to hear himself talk. Plenty of folks using Tesla Modules just fine without any Tesla Electronics. You do however still need to be smart about using any battery and any battery chemistry.


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## AEM (Sep 12, 2014)

So 10 12S Tesla Modules would probably work for a conversion, that would be about 120S 37-43P or 432vdc nominal or 504 at max charge, 120 to 148ah.


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## CKidder (Dec 12, 2009)

onegreenev said:


> EVTV likes to hear himself talk. Plenty of folks using Tesla Modules just fine without any Tesla Electronics. You do however still need to be smart about using any battery and any battery chemistry.


Plenty of folks drive around just fine without wearing a seat belt. Plenty of folks drive a motorcycle without a helmet. Some of those people fly through the windshield or splash their brains across the pavement. That you can do something is not the same as you *should* do something. But, it's true, you can use different BMS hardware if you want. I think the relevant point is that it is crushingly stupid to use lithium cobalt cells without any sort of cell monitoring at all. Sure, use an orion or miniBMS or something different. But, use something. So, your last point is perfectly valid. Yes, you do just need to be smart when using any battery. Teslas have caught fire while using the built-in BMS. I would not want to be around a set of Tesla battery modules where no BMS is being used. It would probably work fine as long as you never over discharged or charged it. But, the module has a built-in BMS with cell monitoring and temperature sensors. Why wouldn't someone use it if it is there?


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## onegreenev (May 18, 2012)

CKidder said:


> Plenty of folks drive around just fine without wearing a seat belt. Plenty of folks drive a motorcycle without a helmet. Some of those people fly through the windshield or splash their brains across the pavement. That you can do something is not the same as you *should* do something. But, it's true, you can use different BMS hardware if you want. I think the relevant point is that it is crushingly stupid to use lithium cobalt cells without any sort of cell monitoring at all. Sure, use an orion or miniBMS or something different. But, use something. So, your last point is perfectly valid. Yes, you do just need to be smart when using any battery. Teslas have caught fire while using the built-in BMS. I would not want to be around a set of Tesla battery modules where no BMS is being used. It would probably work fine as long as you never over discharged or charged it. But, the module has a built-in BMS with cell monitoring and temperature sensors. Why wouldn't someone use it if it is there?



Well usually its because the built in BMS is proprietary and rather out of reach of most DIY guys to deal with. So someting else is required. Even when Jack prattled on about his NO BMS montra he actually did use simple monitoring tecniques to help reduce the chance of any bad ju ju happening. Bottom balancing was the top deal. Then it was a smart charger that could cut off the charge at a predetermined voltage and amperage and then to reduce the top cut off voltage down to a safer place and then have his smart controller be able to prevent him from going below a specified voltage and amperage so never to destroy the batteries while in use. He however did not have thermal points in place and never would do active battery balancing. Bad Ju Ju there. 

So with those things in play amost any battery chemestry could be safely used. I would venture to say one other thing needs to be in play. A way for the system to be shut down in case any of the others no longer work. So something that can monitor the charger/controller and a thermal switch. So if anyone goes out of play its OFF. One other thing is the battery bridge circuit from Lee Hart. It monitors a split pack and if one side goes out and its plugged in from charging then OFF goes the charger. 

So a BMS in many parts. Not just a plain old BMS. I too have seen factory BMS systems fail because they did not monitor themselves. Ruined lots of batteries.

If you have an affordable way for folks to utilize the built in BMS then by all means make it available. Many here though will not go purchase from EVTV. 

Im supprised that you guys are still monitoring this site. 


Im still bottom balancing and low top charging and checking them from time to time. Still going well.

Still using LiFePO4 chemistry as well. Leaf Modules are being bottom balanced and checked before being put into service.


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## CKidder (Dec 12, 2009)

Well, I don't specifically speak for EVTV though you know my work happens to feature there. I'm involved in lots of projects both with EVTV and without so, yeah, I still look at DIYElectricCar.

Most everything is available open source. The ability to use the Tesla modules is no exception. 

https://github.com/collin80/TeslaBMS

But, yes, EVTV will undoubtedly sell kits too. Some people will buy them, some won't. 

It is true that some number of Teslas have burned up even with these BMS boards on the modules. Your guess is as good as mine but I think there are some issues with the Tesla BMS. For one, the fault loop can easily fail open and then will never go active. The fault chain logic should have been inverted. But, it transmits faults over the serial link too so the Tesla main board should know if faults happen even if the fault line doesn't trigger. 

A second issue is that there are two temperature sensors per module but they're on the positive and negative terminals of the module. This groups every temperature sensor in the whole pack into a strip 3" wide in the middle of the pack. The whole rest of the pack has no actual temperature monitoring at all. I suppose a hotspot in the rest of the pack will eventually warm up the sensors that exist but it will happen perhaps too slowly. They really should have taken the time to put either more sensors in there or put the two sensors at the 33% and 66% point through each module so that they're more centrally located and pick up temperature abnormalities more quickly. 

My best guess for the failure mode that burns up a Tesla module is that one cell somewhere will go south and heat up but the voltage doesn't change enough to trip a limit. It's hot but doesn't get close enough to the coolant loop and is in fact too small of a thermal mass to really change the whole coolant temperature. This causes the temperature sensors at + and - to never really see that much temperature rise. In the meanwhile the cell gets hotter and hotter and starts to affect its neighbors. This doesn't trip any temperature sensors until well after the first bad cell is past the point of no return. The cell chemistry is not very friendly. If a single cell goes thermonuclear it'll very easy cause a cascade failure that rapidly gets out of control and voila you've got a fire. The temperature sensors in the module are really only meant to check the whole pack temperature. That's fine for hard driving or charging normally. You'd expect the whole pack to warm up because of these things. A single or few cell failure seems likely to run away long before the temperature sensors could ever find out. The only hope would be for the voltage on those cells to also go crazy. Likely 99% of the time the voltage does go stupid and the BMS catches it. But, what about that 1% of the time where a cell gets angry but the voltage doesn't go over the limit? Still, this entire paragraph is idle speculation and should be given the proper grains of salt.


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## onegreenev (May 18, 2012)

CKidder said:


> Well, I don't specifically speak for EVTV though you know my work happens to feature there. I'm involved in lots of projects both with EVTV and without so, yeah, I still look at DIYElectricCar.
> 
> Most everything is available open source. The ability to use the Tesla modules is no exception.
> 
> ...



I was not aware that you were doing both work away from and some with EVTV. Good to know. I'll check out that link. One other thing that crossed my brain awhile back was even if a cell goes over current and pops its fuse does not mean it still can't go thermal because of an internal short. It can happen and that sort of thing is pretty much something you can't control once it starts no matter what sort of system you have in play. 


Thanks for the information. 

Im going with Leaf Modules myself as well as the CALB cells. 


Pete


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## AEM (Sep 12, 2014)

Currently my idea for a conversion, would be 8-10 Tesla Modules giving me between a 42-64kwh Pack.
I'm deciding between a 2012+ BMW 328i I already have available as my father plans to replace it with a Model 3 or to sell it and convert an FFR 818. I would use the the either the small or large Drive Units with the UMC 3.0 or Gevcu once they are available. 0-60 would be under 6 seconds at least and range at Least over 100 miles. I would definitely have either the original BMS or aftermarket if necessary. Of course if I decide to use the BMW I might drive it for at least a few months before deciding to convert.


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## boekel (Nov 10, 2010)

onegreenev said:


> One other thing that crossed my brain awhile back was even if a cell goes over current and pops its fuse does not mean it still can't go thermal because of an internal short. It can happen and that sort of thing is pretty much something you can't control once it starts no matter what sort of system you have in play.


True, but on the other hand; I've seen some pretty mangled up packs here on the forum and on the news, that didn't catch fire, so obviously they did design them pretty well...


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## AEM (Sep 12, 2014)

So about many Modules would be able to be fit in an 818S or an 818C? I know they've fit about 32kwh of volt modules. Would say 8 or even 10 Tesla Modules be able to fit in one, I like the idea of a version of the 818 designed to be converted to an EV with a floor pan battery since there's been at least 3 conversions. It could use the motors from a D model and use half a pack from a 100DL for about 300hp or so and up to 200 miles of range at least theoretically.


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## Moltenmetal (Mar 20, 2014)

> if a cell goes over current and pops its fuse does not mean it still can't go thermal because of an internal short. It can happen and that sort of thing is pretty much something you can't control once it starts no matter what sort of system you have in play.


That's a very good argument to go with a smaller number of larger capacity cells- MTBF makes the unlikely failure of a cell much more likely when you use large numbers of individual cells. Yeah, I realize that a larger capacity cell is really just a bunch of lower capacity cell plates stacked together in a larger box, but at least then they're sharing the same thermal connection to the cooling system, making individual temperature monitoring more likely to be successful.

Economics is another compelling reason to go with larger format cells. Tesla has made a bad bet in my opinion, and then doubled down on it repeatedly- it is a certainty that numbering up smaller mass-manufactured cells is going to be more expensive than mass-manufacturing a greatly smaller number of large format cells. LG Chem is already reporting $/kWh numbers for their larger format cells which are better than Tesla is claiming to be possible from their Gigafactory, and it's a certainty that it is far cheaper to make a pack from LG Chem cells than it is to make a Tesla pack, even with the robots. Scale matters, and scaling up always wins over numbering up unless something else more important intervenes. I fail to see what that "other more important thing" could be.

LiFePO4 is much more forgiving (with the added benefit of no cobalt too), in return for half the energy density, so it's a poor basis for comparison.

Personally I believe that BMS on every cell (i.e. every group of cells in parallel acting as one big cell) is necessary even with LFP, and is absolutely mandatory when using any of the high energy density chemistries.


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## AEM (Sep 12, 2014)

Not sure if there should be a new thread for this but recently evtv seems to have succeeded in taking control of the Tesla module BMS and designed harnesses to connect the Modules together both both are found in his store though evtv seems to be moving toward using Tesla batteries for home solar rather than ev conversions. Hmm wonder if the 100D Modules BMS is any different from the older 85s.


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## CKidder (Dec 12, 2009)

AEM said:


> Not sure if there should be a new thread for this but recently evtv seems to have succeeded in taking control of the Tesla module BMS and designed harnesses to connect the Modules together both both are found in his store though evtv seems to be moving toward using Tesla batteries for home solar rather than ev conversions. Hmm wonder if the 100D Modules BMS is any different from the older 85s.


Well, we've had the Tesla BMS modules working for months. But, recently we got to a board layout that everyone is happy (enough) with. But, yeah, EVTV is more concerned with home solar than EV conversions when it comes to these modules. The reason for that is simple - the modules are very low voltage (like 22v a piece) so you need a ton of them to use most OEM inverters. There is a reason that the Model S uses so many of them. Because of this if you want less capacity you're in trouble. You end up with 40kwh and 200v and while that might work for a Warp9 it is not going to work for a Leaf or Tesla drive train. However, solar systems are usually designed around 48v or so. That's basically two Tesla modules in series and as many in parallel pairs as you want. That makes sizing the battery a lot easier.


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## AEM (Sep 12, 2014)

CKidder said:


> Well, we've had the Tesla BMS modules working for months. But, recently we got to a board layout that everyone is happy (enough) with. But, yeah, EVTV is more concerned with home solar than EV conversions when it comes to these modules. The reason for that is simple - the modules are very low voltage (like 22v a piece) so you need a ton of them to use most OEM inverters. There is a reason that the Model S uses so many of them. Because of this if you want less capacity you're in trouble. You end up with 40kwh and 200v and while that might work for a Warp9 it is not going to work for a Leaf or Tesla drive train. However, solar systems are usually designed around 48v or so. That's basically two Tesla modules in series and as many in parallel pairs as you want. That makes sizing the battery a lot easier.


Yeah that would make it lot easier especially since there would not be volume constraints with a car. Though I read a comment of yours on one of Jacks blog entries on making a different shapes out of Tesla Modules to make them fit in car. I think you would need a medium sized car at least and to fit in several areas throughout the car to make them fit without intruding into trunk space.


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## Kevin Sharpe (Jul 4, 2011)

CKidder said:


> Well, we've had the Tesla BMS modules working for months.


Has this information been released as open source?


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## Tomdb (Jan 28, 2013)

Yes

https://hackaday.io/project/10098-model-s-bms-hacking


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## Kevin Sharpe (Jul 4, 2011)

Tomdb said:


> Yes


Sorry, I had forgotten that project


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## CKidder (Dec 12, 2009)

Kevin Sharpe said:


> Sorry, I had forgotten that project


Yeah, I think it is linked to in that project but my github repo is here: https://github.com/collin80/TeslaBMS

There's enough code in there for someone to successfully use the BMS with an Arduino Due or Teensy 3.x board. You might be able to do it with an Arduino Mega or something too. The EVTV kit comes with better, upgraded firmware that does things the open source version does not. But, the open source version has pretty much all the real "talk to the BMS" code fully out in the open.


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## GoElectric (Nov 15, 2015)

FYI, I have bought a kit from Jack, and am selling the Orion. I would not normally buy something hot off the press, but the whole think is pretty elegant. There are a few issues with using something basically designed for a solar installation in a car though.

For starters, the harness is not very functional, as our modules are spaced very close together (on top of each other), and he has a foot or so of wire between connections. Just sayin' - not likely he can anticipate such things, but we will likely just use his connectors and make our own harness(es).

Second, His Kit does not support my CAN Elcon (although he promises to do so "by 2021" and likely other chargers too).

Third, there are only two outputs for driving contactors, and with multiple boxes, we have 4 contactors.

Fourth, it would be nice if it could talk to a display, like his GEVCU does, as we have an EVIC display.

Over time I expect to see refinements for others to enjoy, while not being to serious at the moment. Hoping to give Jack some feedback on this and that, but not until we get it running (maybe). I guess if anyone has a question, I might be able to answer it. 

Hmmmmm, thread-jacking. PM or put a question the "Working with Tesla Modules" thread. 

Hoping to start using 12S modules, but then - the above will have to be tossed, or I guess one could have two BMS Slave boards per module.


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## GoElectric (Nov 15, 2015)

EDIT on the above - because we flipped over alternating modules, the asymmetry eats up enough of the cable length to make the harness functional. I think Jack built the harness to fit modules side-by-side, but this is okay and we won't have to re-make it. Sorry about that, Jack.


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