Dead battery?

[ururk]

So... late last summer I purchased a battery. However, because of when I finally got all my parts together, I really hadn't had enough time to assemble, test, etc... the electric bike. I shelved all the parts, including the battery. After some downtime this summer (it has been wet, cold, and not summer-like, plus some family events), I'm ready to start. However, the battery didn't fare too well... as you can see from the pictures, it doesn't look good (click for high-res shots):





It didn't explode, or catch fire (I got the LifePo type batteries), thankfully, but I'm pretty bummed.

So... what is my best course of action? Should I even try to disassemble the pack any further? It is a 36v, 12Ah battery. I'm guessing each of the three sub-packs is 12v. The liquid didn't ignite when water was mixed into it (I scraped a bit away).

 

[tostino]

Ohh sorry about that! Take a look at the voltage of the total pack with a multimeter first of all. See if the cells are low, or if some are dead.

Once you get us the reading we can tell you a little more on how to proceed.

Edit: On closer inspection, I see a ruptured cell, and another with small pin holes in it. Those will not be safe to operate with. If most of the cells are still good, it may be worth it to buy a few replacement cells, and put them in place of the damaged ones. But that is only if you are up for some work, and the majority of the cells are still in good condition.

 

[ururk]

Biggest question - how to determine what cells are good/bad. Do I just remove the rest of the duct tape, and then wipes the cells off? Then, if the cells discharged too much, how would I go ahead with checking each cell? I have the chargers for the packs, but nothing to charge a single cell.

 

[tostino]

Biggest question - how to determine what cells are good/bad. Do I just remove the rest of the duct tape, and then wipes the cells off? Then, if the cells discharged too much, how would I go ahead with checking each cell? I have the chargers for the packs, but nothing to charge a single cell.

Yes you'd probably have to remove the rest of the duct tape to check cells. Do you have a multimeter?

Just get the pack to the point that you can see the connections for the cells, and where they wire them together.

And you will need to measure the voltage of the whole pack still just so we know if there is any saving it.

 

[ururk]

Biggest question - how to determine what cells are good/bad. Do I just remove the rest of the duct tape, and then wipes the cells off? Then, if the cells discharged too much, how would I go ahead with checking each cell? I have the chargers for the packs, but nothing to charge a single cell.

Yes you'd probably have to remove the rest of the duct tape to check cells. Do you have a multimeter?

Just get the pack to the point that you can see the connections for the cells, and where they wire them together.

And you will need to measure the voltage of the whole pack still just so we know if there is any saving it.

Yes... will do.

(should I be concerned about the pack catching fire? I think by this point it would have. They are supposed to be LiFePo4)

 

[tostino]

Measuring voltage will do nothing to make it catch fire if those cells even will to begin with.
They are lifepo4 so it should just get hot and smoke if it does anything.
Just make sure you are not working on anything flamable.

 

[ururk]

Biggest question - how to determine what cells are good/bad. Do I just remove the rest of the duct tape, and then wipes the cells off? Then, if the cells discharged too much, how would I go ahead with checking each cell? I have the chargers for the packs, but nothing to charge a single cell.

Yes you'd probably have to remove the rest of the duct tape to check cells. Do you have a multimeter?

Just get the pack to the point that you can see the connections for the cells, and where they wire them together.

And you will need to measure the voltage of the whole pack still just so we know if there is any saving it.

39.31v across the two discharge leads.

 

[tostino]

That isn't too bad. You have 12 cells in series to get 37v nominal. So 39v is roughly 3.25v pr series string. You now need to measure each series string to make sure they are above low volltage cutoff.

 

[ururk]

Measuring voltage will do nothing to make it catch fire if those cells even will to begin with.
They are lifepo4 so it should just get hot and smoke if it does anything.
Just make sure you are not working on anything flamable.

I wasn't worried about it exploding/catching fire while measuring voltage... I'm just trying to figure out where to store it from now on.

It looks like there are 3-4 cells hooked up together - each group (wired in parallel it seems) has a voltage around 3.2v.

There is one puffed cell - it is a bit hard to tell if there any others are puffed, but I think two packs have at least one puffed cell each, and all three packs have at least one or two damaged cells.

Do I need to desolder each cell to test them individually? I think so, based on how they are wired... see picture. I've never soldered these types of tabs before, though have some soldering experience.



I checked the voltage across the puffed cell -> 0v. But the group it was connected to had 3.2v. I'm not too sure this is correct... if the cells with the puffed cell are connected in parallel, the voltage of that cell should have really been that of the group it was connected to - perhaps the tabs are coated with an insulator.

Thanks!

 

[tostino]

I don't know why the 0v cell didn't pull the others it is connected to down with it.
Sorry I'm on an iPhone right now and it's not easy to convey what I'm thinking.

 

[ururk]

I don't know why the 0v cell didn't pull the others it is connected to down with it.
Sorry I'm on an iPhone right now and it's not easy to convey what I'm thinking.

Understood.

I think there is a plastic coating on the battery tabs... tomorrow I'm going to remove all the tape from the left pack, and try to identify any puffed or pierced cells, and note exact voltages. It will be tricky/dangerous (assuming full current) to do this, but I'll be careful.

 

[tostino]

Yeah just be careful. Don't short anything and you should be fine. I built my own pack with round cells (100 of them) without any incidents. So it doesn't have to be unsafe. You may want to look for a single cell charger to charge up the low cells and make sure they are balanced

 

[dnmun]

you don't have to disassemble anything. use a voltmeter in the 20V range, put one probe tip on the solder bump where the sense wire attaches to the tabs, and then the other probe on the next sense wire soder bump, RECORD on paper each measurement from beginning to end. and the put it on the charger, for as long as it takes to get them charged, then measure again.

why are the edges so beat up? looks like it was dragged on concrete.

BOL, maybe we can help.

 

[dogman dan]

Looks like a lot of puffed cells, bummer. What exactly did you run on the battery? Did the battery sit on the shelf the whole time, or did you top off the charge once in a while. I read of one case where a lifepo4 discharged itself sitting on a shelf for a coulple months, and then a lot of the cells got too low and died. Something was trickling the charge away somehow.

 

[ururk]

Looks like a lot of puffed cells, bummer. What exactly did you run on the battery? Did the battery sit on the shelf the whole time, or did you top off the charge once in a while. I read of one case where a lifepo4 discharged itself sitting on a shelf for a coulple months, and then a lot of the cells got too low and died. Something was trickling the charge away somehow.

It was shelved - so it mush have discharged on its own.

 

[ururk]

you don't have to disassemble anything. use a voltmeter in the 20V range, put one probe tip on the solder bump where the sense wire attaches to the tabs, and then the other probe on the next sense wire soder bump, RECORD on paper each measurement from beginning to end. and the put it on the charger, for as long as it takes to get them charged, then measure again.

why are the edges so beat up? looks like it was dragged on concrete.

BOL, maybe we can help.

I don't know why the edges look so bad. Will do later tonight.