I have been dealing with this problem ever since I got what I thought was a good battery/charger setup. I am a LiPoly addict for their obvious advantages, but am running into some problems charging and maintaining them. I am using this charger to charge my 3 cell packs ranging from 145 mAh to 1020 mAh. The jumpers are set correctly, the packs are made correctly, and the power supply is supplying around 18v.
So I go to the field and fly until I'm out of batteries (being careful not to run the cells down too far), and come back to recharge them. The 560 mAh pack will not charge with the jumper set at 450 (it indicates green, which is full charge and I know this to be untrue). If I set the jumper at 100, it will charge for a few minutes and then indicate full, which is also not possible. I have also had two or three cells balloon up on me. In general the packs seem to be going to hell, and I don't really want to spend any more money until I have the problem isolated.

Here are my questions-
Is it true that if you run one of these cells down to 3v, you should recharge it very soon to avoid damaging it?

Does this sound like the behavior of a cell that has been discharged beyond it's capability?
If it has, is there a way to tell when to stop flying to avoid damaging the cell?

Tonight's experiment involves a very expensive power supply that I am borrowing from work to determine what voltage the cells like to be charged on. I am bringing one of my e-e friends to keep me from hurting myself. Wish me luck.

If anyone has any ideas what might be going on, please let me know.

My, my, that doesn't sound good.

Although it is hard to deplete a 2 cell pack below minimum while flying, it is easier with a 3 cell pack since you'll still have 9V and that may be enough to keep you flying a little longer.

Taking them below minimum will result in decreased capacity. I assume the cells puffed up while charging. Did you notice any decreased capacity before they failed?

Although I can't find anything about it on the Kokam site, some of the Lipo manufacturers tell you to not discharge below 3.V (some say 2.5V), but if you do discharge below that level the cell should be charged at C/20 until it reaches >3.0V. Then charge as normal. I've never seen any info on how long you can wait to do this, it probably doesn't matter.

I would try charging/discharging the cells individually so you can see what you've got. You may have a bad cell or they could be way out of balance. A bad cell will charge up to 4.2V very quickly with very little mah in, and same on discharge. In just a few minutes voltage will drop to minimum with very little mah out. A major loss of capacity. One bad cell will effect the whole pack.

I would check voltage on each cell. Two cells in the same pack should read the same voltage. Then I would charge each cell individually. If each cell worked OK, then discharge and charge them as a pack again to see how they do.

The sausage cells would appear to be from overvoltage during charge. Guessing at it, either the charger output, or a bad cell in the pack could have been pushed it way too high if there was enough voltage difference between the two cells.

While you're checking and charging the individual cells, also check the voltage during the charge to make sure it's in range. It shouldn't exceed 4.23V per cell at any time.
I kinda suspect the charger, you shouldn't have that many cells going 'sausage' on you, even if you discharged them too low a few times.

You don't have to disassamble the packs to charge the cells individually. Make up some small alligator clips to your charge leads. Clip it on the positive pack lead and put the other clip on the negative tab from the same cell. When that one is charged move both leads over to the next cell. Just move across the pack, cell to cell. Watch your polarity. The last one will have the positive lead on the cell tab and the negative on the negative pack lead.

If you get confused a digital voltmeter will check the connection for you before you apply charger power.
Put the red positive meter probe where you think the + lead should be and the black negative probe where you think the - charger negative lead should go. You should read single cell voltage. If the voltage display on the meter has a minus sign in front of it the leads are reversed, if no minus sign connect the charger leads same as you had the meter leads.

Be very careful while doing this !!!!!. I only offer it as a solution since the packs are too delicate to be unsoldering and soldering several times. But go slow and check with the meter before applying charger power each time.

It sounds like a lot of work, but you need to divide in order to conquer. Turn the big problem into smaller pieces and check each in turn. By the time you've done a couple of cells you'll know if it's the charger or the cells. If it's the charger you will also know by then which cells are good and which are bad.

Well that's about .02 worth....... any more ideas anybody?

Jimmy

Bob Selman has one and two cell voltage monitors that go on the plane to monitor voltage under load in flight.

http://users.joplin.com/~bselman/

Dave Lewis has one for a single cell, and soon a two cell.

http://www.homefly.com

It is surprising how low volts under load really are once you start flying with one of these.

Gordon

My problem was the unregulated power supply I was using. The voltage would drop below minimums when the larger cells were attached, and they would only get a partial charge. Still haven't figured out why they were pillowing, but I think I only lost 3 cells.

Now I am using a big fancy power supply that tells exactly how many volts and amps are being used at any given moment. Everything seems to be charging nicely.

Thanks for everyone's help,
-=D=-