What Should I do with My Bad Module?

[Matt]

Hello all,

Last year ai had a battery issue that forced me to switch out module 0 on my MXR. The module has a p group that is virtually at 0 voltage which I suspect is do to a dud cell in that p group. The rest of the p groups are fine. I have had the module since the repair and have taken it to a few colleges to discuss the battery architecture and the Alta bike in general. At this point though I am not sure what to do with it. I don't have a benchtop power supply to charge and balance the module so it has been sitting. It still has ample charge but I know that I am somewhat against the clock to do something with it. My question for anyone on here is what should I do with it? To use it for anything such as a power bank I think I would need to isolate the bad p group and remove that from the line of p groups in series. If I did this would I need to remove the bad cells? Will they bloat and cause issue if I don't? Is the module a total lost cause and just a ticking time bomb with no real purpose left? Any thoughts and ideas would be appreciated.

 

[rayivers]

If it were mine, I'd get out my meter and start reading voltages (p groups, and individual cells if possible), writing all readings down. Then you'll have a much better idea what's going on, and maybe what to do about it.

 

[Judaslefourbe]

Makes an awesome paperweight.

 

[Philip]

If you didn't have a good module, maybe you could wire another p-group of six cells and throw them somewhere at the bottom of the battery.

But you do have a good module already.

I do not think dead batteries would swell up and cause any harm. If they did, that would make all EVs into time bombs.

Mark claimed he had learned to extract and replace individual cells safely. Just do not tell Raakesh.

 

[Judaslefourbe]

Mark claimed he had learned to extract and replace individual cells safely. Just do not tell Raakesh.

For good reasons; it can be extremely dangerous both in the act itself and in the end product you create.
Unless you have a sandpit at home, you would not be able to extinguish the fire it may create.
Shit is no joke.

 

[enjoythesilenc]

If you have a p group at 0 volts, the cell that failed must have shorted internally or the p group shorted as a unit, like with water damage or a loose screw inside the case. I'm not sure if a componet on the circuit board could have shorted the whole group but whatever happened, things must have got hot unless is was a trickle short. There was 70Wh disappearing internally, i think. please check my math

 

[enjoythesilenc]

I think a dead cell is sometimes altered internally with structural breakdown etc. /harmless at 0 volts but could get hot if you try to recharge it. Is there any physical evidence incriminating one cell out of the 5 as to which is the bad cell? Swollen or bulging top, discoloration, soot etc? Maybe trickle charge the p group and use a flir camera (like dirt-e did) to see which cell is heating up. Otherwise have to disconnect them and test, you have a 20% chance of finding the bad one first before unhooking the good ones..

 

[Rashid510]

@enjoythesilenc - 18650s in general dont swell up like prismatics usually. When they go bad...there almost like a small rocket motor.

What I have seen with dead Alta modules (also similar to the ones I deal with now) is some how the cell internal (annode usually) has been deformed/damaged from cell manufacturing and lead to a long term short. At Alta we never really did in-production cell testing, we had the vendor do that.

 

[cory151]

For good reasons; it can be extremely dangerous both in the act itself and in the end product you create.
Unless you have a sandpit at home, you would not be able to extinguish the fire it may create.
Shit is no joke.

The modules we use at Tesla are much larger and hold way more energy than any Alta and if a module starts off gassing or has a "thermal event" you just glove up and throw it in the salt water dunk tank and put the lid on it (not a sand pit in the whole factory). Ive replaced individual cells in packs for racing applications and so long as they are un-potted and lasered bonded/ spot welded Nickel strips its really not that hard.

 

[Rashid510]

The modules we use at Tesla are much larger and hold way more energy than any Alta and if a module starts off gassing or has a "thermal event" you just glove up and throw it in the salt water dunk tank and put the lid on it (not a sand pit in the whole factory). Ive replaced individual cells in packs for racing applications and so long as they are un-potted and lasered bonded/ spot welded Nickel strips its really not that hard.

Unless Tesla some how did not change there Model S design, the Alta module also is designed with passive propegation resistance so if a cell were to go off, it would only hold into one cell and not rip or domino effect into other cells.

Key point. Laser welding. Much easier to work on cells compared to wirebonded cells.