Finding a bad cell?
 

I have a slightly used ib4200 pack and one the cells vented the other day while charging. Now the pack only puts out about 3000 mah and goes flat. Is there a way I can tell which cell is the dud?

two options that i can think of.

1. volt meter
2. much more CTX-D 2.... it has posts/connections for each cell and has a readout. then you'll know which one is bad and isolate it. :nod:

If you have access to a CTXD, DPD, or similar tray, you can check the pack in that. The small clips (not sure on the tech. name) on the GFX can be used to check for bad cells also. A voltmeter will also work.

I'm assuming you don't have an individual cell discharger or you could tell the weak one right away during discharge. So as suggested above, discharge the pack and use a voltmeter to keep checking voltage across each cell - the weak one will drop faster and be lower than the others. It may even be 2 cells. You may see 1.20, 1.21, 1.20, 1.19, 1.01, then 1.01 is the bad one... If you don't have a discharger you can just check volts after the pack dumps. A really bad cell will drop to 0 V while the others are still oK. If you don't have a voltmeter either, the bad cell will often get really hot when charging ... it gets full before the others and overheats. In fact when I have cells with significantly higher temps than others it seems to be a sign they're the weaker cells w/higher IR.

An individual cell discharger is a good investment to keep the pack in good shape longer. Otherwise you keep overcharging the weakest cells, which degrades your packs faster. It's worth it to save your batteries. Even a 20 A duratrax or 0-30 ($40 - 60) is better than nothing. Or $140 or more for DPD, Much more, etc.

That's just what I needed to know. I do have a Smart Tray and a voltmeter, so I should be able to isolate them now. Thanks for the help.

Check each cell with the digital voltmeter. Zero volts equals BAD cell.
I've seen this several times with IB4200WCE cells now.

The indiv. cell discharger method will also work if it can display voltages.
My DPD points them out pretty quickly.

I would like to know this too cause recently I am experiencing dead cells on almost all my IB4200WC packs.... :flaming:

I do have a volt meter but not quite know how to use it properly....correct me if I am wrong here...should I do these steps..?

(1) charge the packs...
(2) discharge the packs by discharger....
(3) after discharged, test each cell by using volt meter
(4) I should see 1.21 1 .20 1.21 ....etc, and if there is a dead cell, I should see 0V....is that correct..? Or I will see 1.01, 0.89...etc?

When I put them onto my smart tray after discharging, I know some of my IB4200WC cells light will turn off alot faster then the rest...and I suspect those are the bad/dead cell....is that correct?

Thanks for the help.......

I got a smart tray 2 also. I think the discharge method could be misleading.... cause the other cells are not getting fully charged so they could dis to .9v before the bad one(s). that method to me is only good if all the cells are getting up to temp/fully charged.... I use to log all the cells..which ones dis'd first but stopped...good to know but the cells change over time and results vary.

I just use my finger (but don't pull it, my farts stink! lol) or the temp sensor to figure out which one(s) are hottest...that is your venting cell(s). it's pretty obivous on my packs which ones are the ventors. 2 will be way over 100 and the others like barely 90 degrees. I got 2 packs now I need to redo org can get all the weaks together..so I only got 1 weak pack instead of 2!

I wish they would make chargers what would charge individually! that would be ideal for the best/full charge..even on good packs. I think somebody makes one but it's outta my price range. Been awhile and forget what brand...anybody know of any?

Spintec makes one

Spintec ICC

thanks!

Nice but 415$ list! on sale 389$ :weird: sweet but I'm not quite that ready to drop that much bread when I need a brushless for the TC.

If the cell(s) in question are totally shot and @ 0v you will notice as soon as you throw them in a discharge tray.

If you can, tray them anyway, watching which lights go out first will indicate which ones are not up to par :)

It's possible the the bad cell has just gone out of balance and isn't actually dead.

So my routine for diagnosing a pack without cycling each cell individually would be...

1. Check individual cell voltages under no load, they should all be around 1.2V - if one is at 0V or at anything well below 1.2V it is out of balance - however IB's can go down to 0V occasionally without failure, and just need coaxing back to life. If a cell is at 1.6V or something even higher than that it is probably totally shot, I have seen a few cells do this (normally cheap stick pack cells).

2. If there is a cell well below 1.2V give a slow charge (say 1A) for a few
minutes, this will normally bring a better voltage into the bad cell.

3. Equalise the pack to 0.9V per cell or similar.

4. Let the pack recover from equalising then charge as normal, monitor the cell voltages, they should be fairly even, if one is way out or appears to have peaked too early (ie its voltage starts dropping and it is hotter than the rest) then that is a BAD cell.

5. If the charge doesn't show any bad cells, discharge as usual to 0.9V per cell, again checking for any unusual voltages, ie a cell dropping low early compared to the others, that would be a BAD cell.

6. If that doesn't show anything and you still think there is a bad cell, break up the pack and cycle each cell individually. Time consuming but guaranteed to get a result.

Well, I found the bad cells and it was pretty obvious which ones were bad. After a full charge, I put the pack on a 20a discharge and monitored the voltage of each cell. They all stayed close in voltage until about 5 minutes into the discharge, when the pack dropped to 5.5 volts. With the load still on the pack there were 2 cells that read .35 volts and the rest were at ~1.21 volts. If I took the load off, all the cells had about the same voltage, so the key was checking the cells under load. I also put the pack on the discharge tray and it confirmed which cells I had isolated as bad. The lights on the bad cells went out immediately, while the good cells held above .9 volts for quite a while.

Thanks again for all the great info.

I'm discharging a pack right now that I think has a dodgy cell. After I charged the pack, I put it onto my DPD, and all of the cells read about 1.44volts or so. after an hour cell 2 is done but all of the rest are at 1.21 or 1.22.

I'm thinking that that cell is pretty bad. Any one agree?