# What are 'good/safe' battery charging practices?



## stealthE (Jan 31, 2016)

**6 Tesla cell set up**

I mean...should I plug the charger in every night? Should I wait till full charge before driving?

I understand charging to 100% will shorten lifespan, and draining below 20% will do the same. So, with 80% to play with...I have set the charger to cut out at 95%. But what if the batteries were drained to 20% SOC, and I plugged it in for 3 hours, then wanted to run to the store. Is it safe to unplug and start driving?


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## major (Apr 4, 2008)

Hi there,

Would you please post the outcome of your previous thread: the Curtis/contactor problem. 

Thanks in advance,

major


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## Sunking (Aug 10, 2009)

Lithiumm batteries work best in the PSOC range. Avoid micro cycles as much as possible.


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## major (Apr 4, 2008)

Sunking said:


> Lithiumm batteries work best in the PSOC range. Avoid micro cycles as much as possible.


Hello Sun,

What is PSOC? What do you define a micro cycle to be and why do you feel that is to be avoided?

Regards, 

major


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## Karter2 (Nov 17, 2011)

OP... Not enough info.
"Charge for 3 hours", means nothing unless you state the charge rate and pack capacity.....and how long that run to the store is !
PS...rapid charge rates also shorten cell life, as does high discharge rates...
So it all depends on the specifics of your installation.


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## Sunking (Aug 10, 2009)

major said:


> Hello Sun,
> 
> What is PSOC? What do you define a micro cycle to be and why do you feel that is to be avoided?


PSOC = Partial State of Charge. Unlike lead acid batteries that must be kept at 100% SOC and immediately recharged after any use to maximize battery life, Lithium technology works best in the PSOC range of 10/90 % SOC.

Micro cycles are left over from the Lead Acid mentality of recharging after any use, even a shallow cycle, and do not go less than 50%, or allowed to rest in any SOC less than 100%.

So what I am saying is do not charge to 100%, and let them discharge down to teens and 20 percentile range before recharging.


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## electro wrks (Mar 5, 2012)

stealthE, You're one of the first to use the Tesla modules in a DIY build. As such you're a pioneer. And we all applaud your efforts. But, you need to be very careful and do your homework on them BEFORE the modules are put in use. These units have ~twice the energy density of most previously used batteries and as we've seen in RickWoodbury's recent posts, can be very dangerous. Tesla has spent many hours and millions of $ to try to make these batteries safe in their application. You're not going to be able to use them in a DIY EV, like batteries with the much safer LiFePO4 chemistry, without paying a lot of attention to charging and safety issues.

For example, are you using the preexisting BMS on each module? If not, do you have or plan to have a BMS? Temp. and voltage monitoring? If there's a fire, do you have a way of containing it and directing it away from the passenger area like Tesla has?

As I said, you're to be commended for your pioneering work, but PLEASE do it in a safe and careful manner.


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## dougingraham (Jul 26, 2011)

stealthE said:


> **6 Tesla cell set up**
> 
> I mean...should I plug the charger in every night? Should I wait till full charge before driving?
> 
> I understand charging to 100% will shorten lifespan, and draining below 20% will do the same. So, with 80% to play with...I have set the charger to cut out at 95%. But what if the batteries were drained to 20% SOC, and I plugged it in for 3 hours, then wanted to run to the store. Is it safe to unplug and start driving?


Tesla wants you to daily charge to a max of 90%. They give you a slider to select between 50% and 100% SOC but call anything above 90% a range charge. People naturally tend to shy away from low states of charge so they don't worry about the bottom end so much.

For longest life it is best to keep the battery near the middle of the state of charge. This might be impractical with the charging setup you have at your disposal. With my Model S I set the slider to 56% and on a daily basis I see the SOC stay between 44 and 56% with normal use. Of course this is 130 miles of range at 50% SOC so with your 6 module setup you will probably have to charge more than I do.

Hope that helps!


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## Duncan (Dec 8, 2008)

Hi Doug
Just out of curiosity does the Tesla do any balancing when you charge to 56% or does it just balance when you do a "range" charge?


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## azdeltawye (Dec 30, 2008)

Sunking said:


> ... Avoid micro cycles as much as possible.


Please provide links supporting claim that "micro-cycling" is detrimental to Li-ion batteries.
This is news to me...
Thanks,


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## Karter2 (Nov 17, 2011)

Sunking said:


> Micro cycles are left over from the Lead Acid mentality of recharging after any use, even a shallow cycle, and do not go less than 50%, or allowed to rest in any SOC less than 100%.
> 
> So what I am saying is do not charge to 100%, ........


Sunking was defining Micro cycles as the practice of keeping the charge at the top of the capacity range.....known to be detrimental to life of this type of lithium cells.


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## dougingraham (Jul 26, 2011)

Duncan said:


> Hi Doug
> Just out of curiosity does the Tesla do any balancing when you charge to 56% or does it just balance when you do a "range" charge?


I don't think it does any balancing of any kind until above 90% SOC. Tesla is not all that forthcoming on information. You can see it does something when it gets near full SOC. The current drops off quickly at SOC above an indicated 90%. Under normal conditions the pack SOC is at an indicated 90% when the pack voltage reaches an indicated 405 volts (4.22 volts per cell). The completion prediction algorithm breaks down when it gets near full and I have seen it alternate between 5 minutes remaining and the estimating time message for a couple of hours. One would guess that it is balancing at this time.

My best guess is that as soon as the pack voltage reaches the indicated 405 volts that the balancing circuits kick in. It is likely that a fault would be indicated if a cell goes above the 4.22 volts when below the 90% SOC. This would be indicative of a loss of capacity in one of the 74P cell groupings relative to the others in the pack.

I do know that when it is well balanced that the charge terminates when the current in the CV phase (405 volts) reaches 5 amps. I've only done this a couple of time and watched it both times.

The only time I can see the battery voltage and current is when I am doing a Level 3 DC charge (Supercharger or Chademo). The car does not show this info at any other time. When using the onboard charger(s) it only shows the AC input voltage and current. When my warranty is up I am going to add a pack monitor of some kind. Maybe just a JLD 404.


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## Moltenmetal (Mar 20, 2014)

High voltage especially at high temperature, is bad for all Li-ion cells. Long periods of time under charge near the end of charging are the worst, with time in storage at high SOC being less bad but still potentially damaging. There are good chemical reasons for this. The higher voltage chemistries including Tesla's should be worse than LFP in this respect.

Low SOC is definitely bad too. LiFePO4 mfgs list cycle life vs SOC at end of discharge, and cycle life decreases sharply if the cells are taken below 30% SOC routinely, and drops even lower at 20% SOC. The reason for this (chemically) isn't clear to me, but I doubt the mfgs publish this without a reason.

What to do in the middle, between 90 and 30% SOC? I charge whenever I feel I might need the range the next day. If it will be sitting for a while, I wait and recharge the night before driving. But when in doubt, I charge. Running the pack to very low SOC ever is riskier to the pack than the odd bit of sitting around at high SOC. It can extend your trip back by a long time even if you can get to a charger before your low voltage cutout alarm goes off on your lowest capacity cell.


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## kennybobby (Aug 10, 2012)

dougingraham said:


> ...
> The only time I can see the battery voltage and current is when I am doing a Level 3 DC charge (Supercharger or Chademo). The car does not show this info at any other time. When using the onboard charger(s) it only shows the AC input voltage and current.


I was under the impression that voltage is the EVSE supply voltage rather than the actual pack. A higher supply voltage is obviously needed in order for current to flow into the pack. Monitoring of the cell voltages using the CAN bus data (see lolachampcar's thread at TMC forums) has shown cells never to exceed 4.2. Here's a time history of cell voltages balancing during a supercharger session.


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## dougingraham (Jul 26, 2011)

kennybobby said:


> I was under the impression that voltage is the EVSE supply voltage rather than the actual pack.


On level 2 using the onboard charger(s) this is true. When Level 3 charging using Chademo with the Chademo adaptor or Tesla's Super Chargers the charging display shows pack voltage and DC charge current.



kennybobby said:


> A higher supply voltage is obviously needed in order for current to flow into the pack.


The pack voltage is 405 at full charge according to the charging display. The onboard 10 kw chargers have a PFC front end which boosts the internal voltage to something above 405. Then the charger bucks down the internal rail to deliver the required current.




kennybobby said:


> Monitoring of the cell voltages using the CAN bus data (see lolachampcar's thread at TMC forums) has shown cells never to exceed 4.2. Here's a time history of cell voltages balancing during a supercharger session.


That is an interesting chart. I wonder how lolachampcar calibrated the CAN data with the real world? I have seen a CAN dump of the pack data and the numbers are arbitrary integer values with no key as to the range. Tesla certainly isn't forthcoming on what the CAN data values represent. You would need to directly measure one of the 74P cells in a module and compare to the CAN data. I would guess that the assumption was made that the cells never go over 4.2 and that was what was used to calibrate the CAN data. The other possibility is that someone looked at the chips in the BMS and figured out the calibration from that. This would not explain why the charging display shows 405 volts as the terminal charging condition during Level 3. 405 volts / 96 cells = 4.21875 volts per cell average. I've seen this 405 volts displayed on multiple cars using multiple superchargers.

I tried looking at the TMC forum but the signal to noise ratio is only about 3% and its not worth wading through the trash. I think I will go see if I can contact lolachampcar and find out how the data was calibrated.


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## kennybobby (Aug 10, 2012)

The calibration and scale factor for conversion was done by the whiz kid, Jason Hughes, known online as wk057. 

He has the knowledge, skills and abilities to trust his data. He designed and built a solar home in NC using 2 85kwh packs as storage and uses it to charge he and his wife's P85(D)'s. He bought salvage tesla parts (IP and Main screen) and was able to gain root access to the operating system. He wrote a document explaining the CAN ids and how to convert from binary to engineering units, etc. He captured the autopilot code and installed it on his wife's non-AP car and got it working. 

He and most of the tech savvy guys have left that forum due to low S/N, but if his posts are still up then those are worth reading. He has his own website now, http://skie.net/skynet/projects/tesla, if you want to read about his projects.


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## electro wrks (Mar 5, 2012)

Well, if you blinked last night you may have missed that stealthE had a serious fire incident with his EV. The powers that be that control this forum apparently have chosen(probably wisely for liability reasons) to delete the thread detailing the fire. Still, it's kind of Orwellian or like those old Soviet photos where people no longer in favor were simply airbrushed out! 

In the spirit of DIY (isn't that what this forum is about?), it would be helpful to recap what went wrong so that other DIYers might avoid making the same mistakes. Is that OK? Or, am I just going to be airbrushed out?


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## kennybobby (Aug 10, 2012)

Well can we identify the mechanisms by which these cells can fail and get so hot that they might ignite?

1. An under-discharge event below a certain threshold voltage followed by subsequent charging.

2. An over-charge event above a certain threshold voltage, possibly with or without subsequent discharging.


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## Karter2 (Nov 17, 2011)

Yes, i was a little pissed that the thread was nuked...Why ?
There were huge warnings and lessons to be learned from that thread, it may just have prevented similar incidents in the future when folk see that a Lithium EV pack should not be underestimated in its ability to surprise you.
Tesla modules are powerful packages of energy , and need to be treated with the care you might afford.... a bucket of gunpowder !


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## AntronX (Feb 23, 2009)

That thread can be found in google cache... I can post the link but not sure if I wanna get banned.


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## electro wrks (Mar 5, 2012)

This intense fire was a real eye opener for me. Think about it. If this happens more often, more people and property will be put at risk. Insurance companies might refuse to cover DIY EVs. It could be a nightmare for companies like Telsa and taint all EVs.

OK, to reconstruct the events as I recall what happened, here's what I've been able to glean from posts on this Forum and ES. I'll need some help with this. If anyone wants to fill in or correct details, please chime in.

1. The OP was constructing his first build.

2. He chose to use recycled Tesla battery modules that are potentially much more dangerous than other batteries with safer chemistries.

3. A BMS was not used , even though the people who sold him the modules strongly recommended he use a BMS to moniter each of the 6 series strings in each module for a total of 36 monitoring points. This is apparently what Tesla does, along with temperature points throughout their 16 module pack.

4. Only module voltages were monitored manually and not the series strings in each module and no temperature points.

5. The battery box was constructed with no firewalls between the modules. From what I can tell, the modules were stacked in the battery box like bricks, 2 stacks of 3 with nothing in between them. From what I've seen, it looks like Tesla uses 2 layers of metal and a layer of fire resistant, silicone/ mica sheeting around each module.

6. After a long charging cycle, it was noted that one module had a lower voltage than the other 5 in the series string. Now this is where I need some help. Would the overcharging and overheating that obviously occurred at this point be in the low voltage module or the others? 

7. In any case, since there was no BMS or manual monitoring of the temperature or voltage in the 6 series strings in each module, a cell or cells in a string overcharged, overheated, and caught fire. Would the fusible links connected to each cell normally prevent this? Was this safety feature defeated by having the modules stacked close together as was suggested by others?

8. The final problem was that the battery box apparently was not designed to contain the fire and direct hot gases and flames away from the passenger compartment. The OP didn't have enough time to move the vehicle out of his garage. Maybe it wouldn't have mattered with the rapid spread of the fire from the modules being stacked so closely together.

Talk about a cautionary tale. More Tesla Model S modules are hitting the secondary market and those from the Model 3 a few years from now. This could be a real disaster if people don't heed safety protocols and pay more attention to their DIY builds.


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## Karter2 (Nov 17, 2011)

If its any help, this is "my recolection" of the events..

".....6 Tesla modues, all of which were just bottom balanced to 18v, and they were all on the charger when they exploded.
Here is what I know: after driving the jeep, one module was at 18.7v while 5 were at 21.7. So I bottom balanced all batteries to 18.16, re installed the batteries into the Jeep. Plugged the charger in for 20 hours. I was running a Thunderstruck TSM2500 charger (programmable). I had my laptop connected to the charger the whole time so I could monitor the charge. After 20 hours of charging at was at 141v. Which was well below the 149.5v charger cut of voltage.
So:
11:45am - I check the individual module voltages and here are the results: 5 modules at 23.7v and 1 at 23.3v (this module is the same module, that was at 18.7v before the balance)
11:46am - come back into house to make a post about why is one battery still low...after the balance. 11:47am - we heard a pop, followed by another one 10 seconds after. I ran out to garage (attached) to see a small fire at the back of the Jeep. As soon as I seen the fire I opened the overhead door (panic) to get jeep out of garage. By the time the door opened, it was explosion after explosion and monster fire....."

I dont know how or why he "bottom balanced". Modules without cell level 
readings ?
I think lack of "cell level" monitoring or checks, ( and obviously lack of BMS), was a major factor in this situation


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## kennybobby (Aug 10, 2012)

Hey Karter,

Can you 'recall' what i posted there--i can't seem to recall it exactly. thanks, kenny


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## Duncan (Dec 8, 2008)

Hi Guys 
Lighten up
I deleted the thread at the request of the OP 
IMHO you each have that ability to ask for one of the Admin's to delete YOUR thread if you think it may be a problem for you

So there is no institutionalized cover up - just some poor bugger who posted too much and regrets it


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## kennybobby (Aug 10, 2012)

That seems reasonable, and i don't see any problem with it.

However i didn't make a copy of what i posted and would like to recover my writeup if possible. i made some calculations and wrote up a bit of analysis from the data, if nothing else for my own records...


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## Karter2 (Nov 17, 2011)

Duncan said:


> Hi Guys
> Lighten up
> I deleted the thread at the request of the OP
> IMHO you each have that ability to ask for one of the Admin's to delete YOUR thread if you think it may be a problem for you
> ...


 Poor protocol !
The concept of THREAD "ownership" is a new one on me !
A poster may have some control over his own POSTS , (edit, delete , etc) but not over any of the replies.
Even if a poster starts a thread it doesnt give them authority over any subsequent posts to that thread.
It should not be possible for any one poster to have another members posts deleted if he doesnt like the way the thread develops.
Its fine for a thread to be deleted by a Admin for some extreme reason, but it might be reasonable to expect a notification / explanation for other contributors to know whats happening.


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## Karter2 (Nov 17, 2011)

kennybobby said:


> That seems reasonable, and i don't see any problem with it.
> 
> However i didn't make a copy of what i posted and would like to recover my writeup if possible. i made some calculations and wrote up a bit of analysis from the data, if nothing else for my own records...


Kenny, my memory is getting clearer...

"".....Hindsight is 20/20, so let's figure it out.

So one module was at 18.17 OCV (~3.03v/cell) after driving around for the day--but what you don't know is how low that module was pulled while you were driving. They will rebound after being pulled low, especially with the other modules in series to pump current into it and bring the voltage up. Now if it was pulled below 15 while driving, then metal dentrites will form and grow during the reversal of current during charging. The dentrites puncture the plastic separator and short the cell internally and they catch fire.

The low module was pulling itself and the entire pack down thru the internal shorting, which is why it was lower than the rest and the pack wasn't "fully charged" after the 20 hour charge.

141 = 3.917 vpc, which would normally be a safe charge voltage

149.5 = 4.153 vpc is pushing it close to the edge

155 = 4.306 vpc seems over the edge....""


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## kennybobby (Aug 10, 2012)

Thanks Karter you have a good memory.

My theory outlined above seems to fit all the observations that we were given.

i don't think overcharging was involved here at all.


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## Duncan (Dec 8, 2008)

kennybobby said:


> i don't think overcharging was involved here at all.


I would describe it differently
The modules were X serial Y parallel - in one module a cell had died and become effectively a short circuit 
(which is the way my Headway cells died when I over-discharged them) 
That did not cause anything too violent - or even noticeable - probably because the cells in parallel with the dead one were very nearly discharged 

Then on charging the that cell/parallel stayed at zero volts
So the rest of the module were being charged to a higher voltage than the OP thought


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## eric1565 (Feb 28, 2015)

I think the setup had something to do with the fire. He had 3 modules stacked with foam inbetween them. The bottom module had 100 lbs ontop of it with foam holding it up. If you look at the modules they have little plastic standoff's that protect the fuse wires. They are small, but do the job. But if you have that extra weight and foam is the supporting member, maybe it crushed and then bent/broke fuse wires. That could lead to the initial imbalance. Not sure why after 20 hrs of charging it did not over charge the cells... but if he did damage fuse wires, and drove it, he could have over discharged the cells causing the internal short that would cause them to always be lower, and create heat during charging.

But stacking modules with no support is not a good idea. At home I only stack them 2 high, and that is with no dynamic loads like you would see during normal driving. 

my 2 cents.


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## richcj10 (Aug 22, 2016)

Wish there was pictures. 

As a "engeneer" who works at a battery management company this sounds more of a electrical fault. Something got disconnected and touched. 

I don't know how your pack is put together but I always avoid parallel cells. They can cause really weird shit to happen. When I built a pack for a F1 car we used parallel strings. (and monitored the current of the parallel strings) If you must use parallel batteries, fusible links must be used.


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## Sterling2015 (Jun 24, 2015)

I feel bad for folks having LCO battery fire mishaps, but it's very fortunate for others thinking of doing the same and taking heed of the warnings and experience.

Would like to help these folks recover what insurance doesn't cover in loss of projects since I directly benefit from their "testing" and research.

BL: Now with many Model S salvage parts available (eRepairables for example) and temping ebay sellers of hacked Tesla modules, ( http://www.ebay.com/itm/252404811699 ), are all DIY EV builders doomed now because people are going to be blowing up their cars and setting houses on fire? After the first fatality, regs will start.

Appreciate the great info here, learning a lot from others sharing their experience.

Starting self study on Lithium Battery Management Systems, wish me luck.


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## sholland (Jan 16, 2012)

kennybobby said:


> I was under the impression that voltage is the EVSE supply voltage rather than the actual pack. A higher supply voltage is obviously needed in order for current to flow into the pack. Monitoring of the cell voltages using the CAN bus data (see lolachampcar's thread at TMC forums) has shown cells never to exceed 4.2. Here's a time history of cell voltages balancing during a supercharger session.


Where can I find a link to the original source for this animation? It's interesting data...


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## sholland (Jan 16, 2012)

Never mind, I found it:
post #48 - https://teslamotorsclub.com/tmc/posts/1355946/


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## electro wrks (Mar 5, 2012)

Sterling2015 said:


> I feel bad for folks having LCO battery fire mishaps, but it's very fortunate for others thinking of doing the same and taking heed of the warnings and experience.
> 
> Would like to help these folks recover what insurance doesn't cover in loss of projects since I directly benefit from their "testing" and research.
> 
> ...


Apparently, part of the problem was the person with the fire listened to some bad advise. He was told that a BMS was not necessary, and that bottom balancing was all that was needed to safely use the Tesla modules. One of his modules had a lower voltage than the other 5 in his pack. AIR, that module had a voltage at or near the level corresponding to zero battery capacity. Apparently, he tried to bottom balance the rest of the modules to match this lowest voltage module. He then charged them all in a series string to the pack voltage. After a ~20 hour charge, one or more cells in one or more of the modules must have overheated and caught fire. Was the overheating and fire made worse by the modules being tightly stacked as eric1565 and others have pointed out? Who knows?

It seems like bottom balancing did not work in this situation. The larger question is would a BMS have caught this problem and shut the charger down? I know some people(still) are adamant about not using a BMS. Presumably from a bad experience with early BMS's? From what I've seen virtually all manufacturers, using these cells in a pack, have some form of BMS. This includes cordless tools to Tesla. The rare exceptions are the cheap 24-48V bicycle packs from the far east.

What's been the experience of others selling and using these modules? Bottom balancing only? BMS's? Now's the time to work this out before as Sterling2015 says: " DIY EV builders [are] doomed"


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## AntronX (Feb 23, 2009)

Due to the way cells are paralleled in Tesla modules, cell stack voltage monitoring is mandatory for safety. Each module has 444 cells in 6S74P arrangement. Each cell in parallel 74 cell group is connected to the busbar by a pair of thin and fragile aluminum "fuse" wires of only ~0.3mm in diameter. I believe there is a high change these thin fuse wires can be accidentally damaged by less then careful "DIY" handling of the battery module. What happens next is you get 73 cells or less in each parallel group that will get overcharged during charging in series with other good parallel cell groups. If you are not monitoring voltage on each of 6 cell groups per module, you will not know that some cells in the module are being unbalanced. From the way StealthE described how quickly the car got engulfed in flames, it seems to point at many cells burning up simultaneously. ~70 overcharged cells all popping at once will create a lot of heat very quickly, enough to start thermal runaway of entire battery pack. 

The solution to safe use of Tesla battery modules is to use BMS to monitor each cell group voltage and have it automatically terminate charging or discharging if cell voltages get out of safe range. That's it.


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## electro wrks (Mar 5, 2012)

This guy is trying to make own BMS for the modules:https://teslamotorsclub.com/tmc/thr...om-bms-for-tesla-battery-modules.51095/page-4

This is after he apparently, in vain, tried to talk to Tesla about using the stock Tesla BMS. This includes the PCB attached to the end of each module. Is there anyone else trying to hack the Tesla BMS or making their own system? Or, using an existing system? This seems like a real problem that needs to be solved before DIY community can safely use these modules.


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## AntronX (Feb 23, 2009)

electro wrks said:


> ...Is there anyone else trying to hack the Tesla BMS or making their own system? Or, using an existing system? This seems like a real problem that needs to be solved before DIY community can safely use these modules.


Tesla stock BMS boards should be hackable. The model number of the microcontroller on there is known. In case the micro is locked and cannot be reflashed, it could be hot air desoldered and replaced with another blank one. I have one OEM board that I was going to try to reprogram, but never find the time/willpower to do.


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## AntronX (Feb 23, 2009)

electro wrks said:


> ...This is after he apparently, in vain, tried to talk to Tesla about using the stock Tesla BMS.


You have to understand Tesla Motor's position here. If they help someone to modify some salvage part, it opens them up for liability if the part causes property damage. The best they can do is to simply leave the fuses on micro controller unlocked so that it can be reflashed with custom diy firmware without any soldering.


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## sholland (Jan 16, 2012)

I made my own a while ago, and even tried to get it funded on Kickstarter. While it wasn't designed for Tesla modules only, the first test pack was built with Tesla modules, and it easily replaced the Tesla boards. It is a completely open system and does not interface to Tesla's BMU at all. Though more complex, it is a smaller board than Tesla's.

Sadly the Kickstarter campaign failed, but the boards have found some nice homes in several prototype packs. I'll be using it on my own pack soon. 

The chips and reference designs are out there if you know where to look, so there a several solutions.


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## electro wrks (Mar 5, 2012)

sholland said:


> I made my own a while ago, and even tried to get it funded on Kickstarter. While it wasn't designed for Tesla modules only, the first test pack was built with Tesla modules, and it easily replaced the Tesla boards. It is a completely open system and does not interface to Tesla's BMU at all. Though more complex, it is a smaller board than Tesla's.
> 
> Sadly the Kickstarter campaign failed, but the boards have found some nice homes in several prototype packs. I'll be using it on my own pack soon.
> 
> The chips and reference designs are out there if you know where to look, so there a several solutions.


Somebody really needs to make this happen so us metal pounders out here can move the DIY EV scene towards practical 200mile+ range EV's.


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## sholland (Jan 16, 2012)

My development partner and I (he's the SW guy, I'm the HW guy) may go back to Kickstarter again sometime, but honestly we're too busy working on projects that came about because of the exposure from the Kickstarter campaign.

There is definitely a need. If there's enough interest, we can try to sell just the board and some basic code to start from. The full SoC/SoH algorithm sits in a higher level controller, and is where all the development effort is. If someone was interested, the ability to scale to a full-blown OEM grade system is possible with the addition of an ECM, current sensor and (optionally) insulation sensor.


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## electro wrks (Mar 5, 2012)

Well, it's been about a year since the big BMS debate. Now, anybody can buy Tesla modules for a 1000 bucks each on ebay and burn their garage down, or worse, because they're not using a BMS. I think it's time.


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## sholland (Jan 16, 2012)

Here's an early prototype board on a Tesla module...


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## AntronX (Feb 23, 2009)

sholland said:


> Here's an early prototype board on a Tesla module...


I went through your old kickstarter listing and even though your monitor boards were ~$70 a piece which I think is a little high but not bad, you only included the host controller for the boards in your top tier 108 cell $2249 package which I am sure was a deal breaker for many people who just wanted a plug and play solution for their low voltage DC systems with 36 cells. Make a complete plug and play 36 cell package for ~$600, lower your goal to $35k and try again. I will be up for something like that.


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## sholland (Jan 16, 2012)

The point of the Kickstarter was to try to get the build quantities high enough to drop the price a little lower. All the additional items (IVT-MOD current sensor, MotoHawk ECM and Bender iso165C) in the full systems were just being sold at cost.

We streamlined the reward levels down to a few more popular series cell counts, and I think the 36S full system was one of the ones that got cut out. I think with the controller it comes to around $1049. This is still far cheaper than ~$1500 for another widely available BMS with 36S cells and 60 thermistors.

I don't think we currently have the resources to support too many more full system customers at the moment. I was thinking we would just make the individual BMS boards available with some source code, and leave the user to come up with their own pack controller solution. A chipKIT Max32 Arduino board can talk to these that anyone could use as a foundation for their own host controller. At the very least it would make basic voltage monitoring available.


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## JCDavis (Mar 23, 2017)

Hello all and forgive me for reviving an old thread. I have been working with Tesla Model S modules for off grid storage for the past few months and thought I would share some of my experience. 

My packs are slightly different as I am mainly using 5P2S and 10P2S configurations. So, 10-20 modules configured in ~48V configuration. I have primarily used modules all from the same pack together, or carefully compared capacity so that they were closely matched.

Regarding cell level monitoring: It is also my experience that the fusible wires are extremely fragile, and obviously critical. I have found that after about 10 mid capacity cycles, all my cell voltages in a given, matched pack, were maintaining within .001V with no active management. Excellent in my opinion.

One thing that happened: I had one module that during initial examination had odd cell voltages at the volt sense wires. I found that one of the ultrasonic welds to the bus plate had failed. When I checked the cell voltages, one cell was a full volt lower than the others in the module, and very low. I did carefully bring it back up into balance manually. 

Looking closer, I found corrosion on that module. One thing that I believe is key to the Tesla pack is that it is sealed from moisture. Might even be purged with some inert gas. My theory is that this wire lost connection while still in the car, and the BMS was trying to incorrectly balance the pack. This is just a theory and I haven't looked much closer at the health of the pack.

All that long winded background was to say that it sounds like the low module in the unfortunate fire incident could very well have been due to damaged fusible link wires or an otherwise unbalanced module.


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