RE-Building A123 Packs

[JThiessen]

I have 3 A123 packs that appear to have some bad cells (I have another thread on that). Today I want to take one of them apart and I need to find the bad cell. They are 2S2P packs, and the last charge only took them to 3.3V.
1) How do I check for the bad cell? Do I have to completely disassemble the pack? Or can I use a multimeter to measure each cell somehow (while its still assembled)? I'm fairly certain I can figure out which "side" the bad cell is on, but then how do I isolate which one is bad.
2) Once I figure this out, I want to try to charge that cell. How do I manage this? Should I solder on a temporary plug? Somehow clamp on some wires? Can I do this with the pack assembled?
3) When taking apart packs, I assume I should have my iron on high. I've seen something about de-soldering braid. What is that, and should I use it?
4) Anyone want to volunteer for this???!???!!!

[JThiessen]

Here's one of the packs. The bars dont look like they were soldered on, but it could just be a small amount of solder behind them (there are a few little "punch" holes in them). The cells with 0 volts are on the left.

[lincpimp]

Just use the multimeter on each cell. Most meters do not care if you reverse the polarity. So put the black probe on one end of the cell and the red one on the other end. The good cells will read higher voltage than the bad ones.'

The tabs are resistance welded on, the only ways I have found to seperate these is to slowly wiggle the cell back and forth and the tab will eventually come off. You can solder to the cells, but you have to be careful. I usually leave the tab on the cell, and just cut it off in the middle where it bridges to another cell and put the solder on the tab...

[JThiessen]

Measuring them was easy. Thats how I figured out which were bad and which were good.

Now on to how to fix them. If I can figure out how to charge those cells without taking the whole thing apart, I'd be really happy.

[lincpimp]

Originally Posted by JThiessen

Measuring them was easy. Thats how I figured out which were bad and which were good.

Now on to how to fix them. If I can figure out how to charge those cells without taking the whole thing apart, I'd be really happy.

The paralled cells will have to be seperated at least on one end to charge. Some small alligator clips work well, that is what I use to charge individual lipos.

[JThiessen]

I put one cell on the charger, and it looked like it was going good, got it up to about 1.2V, and then the charger gave that "output voltage too low" error again. Wish i knew what that was all about (the manual doesnt say anything). BTW, had the Duo set on A123, 3.3V, 2300maH, .5amp.

Guess this could be the bad cell.

[JThiessen]

Originally Posted by lincpimp

The tabs are resistance welded on, the only ways I have found to seperate these is to slowly wiggle the cell back and forth and the tab will eventually come off. You can solder to the cells, but you have to be careful. I usually leave the tab on the cell, and just cut it off in the middle where it bridges to another cell and put the solder on the tab...

So have you had any that have come loose? There appears to be four spots where its welded. I had one of them pop loose on what appears to be one of those, possible two.

When you made your packs, were they 2S2P config? I'm asking because the center tab connected all four batteries together. It's now cut in half. I'm uncertain how to approach soldering that back together. I'm not certain what to use to solder the other end either...should/can I just use a normal battery bar? I've seen a thread about someone using desoldering braid for this purpose.

[JThiessen]

I got the pack put back together again (I'll call this one - Humpty). I used braided copper desoldering wire to join the packs together again - worked pretty slick (I read about doing this on a thread here somewhere).
Balance charged it, and its sitting at 3.30 and 3.31V.

So all in all, the first one was a success so far.

I also have to thank those that recommended the Hakko Soldering iron to me in another thread. I never would have accomplished it without a good iron.

[JThiessen]

I pulled one more pack apart last night and found it to be the same end of the pack that was bad. But these cells wont take a charge. They run up to about .13V, the charger gives the low voltage error, and I end up restarting at zero. Attempted several times..guess I'll stop by the LHS and pick up a few cells (they have them for 19 each - not a good price, but.....convenient).

[Arct1k]

try rclipos.com

[rcmonkey]

Excellent, thanks

[suicideneil]

Hands up who wants to hear something unpleasant about A123s and their life span:

http://www.dansdata.com/gz042.htm


Oh crap...

[JThiessen]

I dont think that was alarming at all. I'm not sure anyone on here expects their packs to last (in use) more than about a year. I know I sure don't. We (RC'ers) probably use/abuse our packs harder than anyone else does.
But what he said about the 3-4 year expectancy looks to be dead on. These packs I bought are now 3+ years old, and are probably on their last fizzz (thats gotta be an official electrical term, right?)

While I'm a little pissy about the age of the packs I purchased, I did purchase them for basically bottom dollar. Sometimes a good deal is in fact too good to be true.

I've got 400 in Lowes gift cards save up.....waiting for them to start carrying Dewalts 36V line - that is unless the DW finally decides she wants that masterbathroom finshed.....

[rcmonkey]

I checked my packs today and guess what - Feb 06 Even more money needs to be spent now to get my XB8 running now

[jhautz]

Originally Posted by JThiessen

I dont think that was alarming at all. I'm not sure anyone on here expects their packs to last (in use) more than about a year. I know I sure don't. We (RC'ers) probably use/abuse our packs harder than anyone else does.
But what he said about the 3-4 year expectancy looks to be dead on. These packs I bought are now 3+ years old, and are probably on their last fizzz (thats gotta be an official electrical term, right?)

While I'm a little pissy about the age of the packs I purchased, I did purchase them for basically bottom dollar. Sometimes a good deal is in fact too good to be true.

I've got 400 in Lowes gift cards save up.....waiting for them to start carrying Dewalts 36V line - that is unless the DW finally decides she wants that masterbathroom finshed.....

I thought that Dewalt went away from a123 to some other off brand of LiIon cells. I could be wrong, but I'm pretty sure i read that somewhere. Te Dewaly packs they are making now dont contain real a123 any more.