Sir Fliesalot

My Feedback: (2)

I have four PolyQuest 4000ma 3s packs and all four have had one cell go bad at the same time. The weird thing is they seem to charge OK, they show 12.6 volts and take in 3.2 ah (which isn't great) but if I discharge them at anything over 4 amps (1C) one cell will drop below 3v after 20~30 seconds. It brings the pack down to 8.2v real quick.

All four packs have only 11 cycles, been charged with AF109 and PQ PCM guards, Never been discharged more than 10C and have generally been babied to last. I usually charge two at a time on one AF109 charger set at 8 amps.

Is there any hope of recovering the bad cell?
Anyone heard of this before?

jasonwang3a

according to the discharging result, the cell is bad, if the bad cell is not swollen, you can try to resume the capcity through charging at a smaller current such as 100mA,

mrasmm

are the pq packs the ones that have the balancing chips built inside? I can't remember

The main thing I would think of is are the cells that are going bad more confined or somehow running hotter than the other cells? Also are you balancing the cells when you charge them?

If they only have 11 cycles on them I owuld see what you can do about returning them.

It sounds to me that you either ran into a really rough batch, or somehow something that you're doing is making the one cell go bad. That is a good q as to what it is though.

If the pack has been below 2.75v on that cell, it would really be a gamble to bring it back, but I agree with jason about if you want to try to bring it back, take it easy and slow.

Sir Fliesalot

My Feedback: (2)

No I don't think they have the balancing chips in.

They didn't seem to be swollen but the bad cell did heat up while discharging and more than 1C

I've always charged them with the PQ PCM Guard and never discharged past half capacity and I've even checked them with an AF Blinky. The only things I can think of are either they were from a bad batch of cells or the PQ PCM guard is messing them up but that would mean a bad batch of PCM Guards since I have 4 of them charging the the packs. I charge two packs at a time, each connected to a PCM guard and then to a Y connector and then to an AF109 set to 8 amps. There never seemed to be a problem charging and I was told this would be fine. Any thoughts on charging this way?

The good news is I bought them from Hobby Lobby. They said to send them in and they'll send me some 3700's as replacments. That's a great company for you. One that stands behind their product!

mrasmm

hrm I know nothing about PCM gaurds, so correct me if you know better than I do but from what i read over on hobby lobby they aren't balancers just cut offs, so if any one cell reaches 4.2v it cuts the whole pack off.
http://www.hobby-lobby.com/polyquest.htm

"Overcharging a Lithium battery is dangerous, it can ruin the battery and can cause a fire. PCM Guard monitors each cell in the pack and will disconnect the battery pack from the charger if any cell exceeds 4.2 volts. Order the PCM Guard that matches the number of cells in series in your pack."

Also with your charging setup if one battery reaches full before the other does and the gaurd shuts it off, then you're left with one pack charging at 8 amps =/ or 2c

that's a couple of things that come to me off the top of my head.

Sir Fliesalot

My Feedback: (2)

mrasmm - I think you may be right! I had read it as if it would charge each cell to 4.2v and then cut off that CELL while still charging the others. The instructions say "Protective Circuit Module (PCM) is a voltage-limiting-device that prevents each cell from overcharging.". I'll have to get that clarified from Hobby Lobbys tech people. The voltage always shows 12.6v at charger shutdown though so wouldn't the final voltage read lower if one cell reaches 4.2 but the others don't?. Also the packs never got warm during charge. I always check temps while charging. It's still a mystery but were getting somewhere!
Thanks

mrasmm

no problemo. you might also try checking the individual cells as they are done charging by testing the balance connector.

Something has got to be up because all the same cells on all the packs are going bad. now to figure out who the gremlins are and how to exterminate them =P