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Pumpkin drop event

My 4S fell from the sky and is now a 3S?

Duck

Active member
#1
My first flight on my new quad and I accidentally disarmed about 5 feet up over gravel. Everything seemed OK but the battery had a few minor scratches in the plastic and the outer most clear layer was cracked. I was coming in to land anyway so I just put the battery away. When I put it in my charger at home the charger reported an error. I checked the cells and the 3rd cell reports the same voltage as the second and the total pack voltage reads at ~11V. So using a multimeter on DC voltage, I put the ground on the first pin and they read: ~3, ~7, ~7, ~11 which does not seem right. I also did a continuity test and both of the pins 2 & 3 on the balance connector report being connected. What is going on? The only thing I could think happened is the cells got bridged internally and, luckily without exploding, balanced each other out.

Is that possible? I looked real close at the balance connector and the pins don't look bridged there. I don't know how to take it apart safely to be 100% sure. Right now the battery is in my bat safe, but is my best option to discharge and toss it?
 

FDS

Well-known member
#2
It’s hard to check individual cell voltages with a multi meter, a cheap lipo battery checker will do a reliable job. You want the individual cells to be +/- 0.1v of eachother. You could well have destroyed a cell.
Until you fully know what’s up with it you are right to be cautious. Usually if one cell goes then the pack is dead and needs to be replaced.
 

tamuct01

Active member
#3
I had a similar issue when I crashed a plane and the center cell of a 3S pack was stabbed by the motor shaft. Nothing was obviously wrong until I went to charge it the next time and the center cell was completely dead. I was able to salvage the other two into a serviceable 2S pack for my 3D printed F1 car. Be sure to take all sensible precautions if you decide to cut the cells apart and make a new pack.
 

Duck

Active member
#4
My cheap lipo checker did not like the pack. It reported ~85v on that pin. I didnt think the decimal could move for cell voltage. Anyways, it seemed less trustworthy.

Turning into a real 3s woudnt be so bad but I would not trust myself opening the pack and if the cell is really damaged, or bridged, leaving it there doesnt seem safe either. I guess I should drain it and bring it to the haz mat drop off as even the nice 4s pack is not worth a fire.
 

FDS

Well-known member
#5
Absolutely. I use a cell checker/balancer for all testing, some chargers also have a cell reading capability. Mine cost about $15 and has been well worth it.
 

Duck

Active member
#7
I was going to try Batteries + near my house. The county also has a haz mat collection event every quarter that also takes things like paint thinner, CLFs, etc. It just takes planning a trip on that particular day and remembering to go.

RIP my wonderful 4S. I'll replace you but you will be missed.
 

Bricks

Well-known member
#8
I had a similar issue when I crashed a plane and the center cell of a 3S pack was stabbed by the motor shaft. Nothing was obviously wrong until I went to charge it the next time and the center cell was completely dead. I was able to salvage the other two into a serviceable 2S pack for my 3D printed F1 car. Be sure to take all sensible precautions if you decide to cut the cells apart and make a new pack.
I did the same with 2 3s 2200 packs pulled them apart and made one good 3s pack now I have 1 cell waiting until I destroy another 3s pack.