[ShAdOw]-[HeLiX]

Firstly sorry about the double post, I was meant to put it in this section..so if you're a moderator please delete my other post in the common sense RC support section
OK <copy-paste>:
I currently have two 10C 11.1V 2200mAh LiPo battery packs, but for no reason at all one isnt working quite right.
Upon charging the pack, I have noticed that although the voltage is brought up to a nice 12.6V during constant current charging (at this time it has pumped about 400mA into the pack..a lot less than usual), then it continues to charge at variable current for about another 150mA before it declares the pack as full.
I have run about 2 (and am currently running another) slow-discharge-slow-charge cycles, but the pack still doesnt accept the proper amount of amps.
When I use my charger to discharge, and set it to discharge at 1C or 2200mA, it only discharges at 1.7, slowly bringing the rate up as the battery discharges. By the time it is at 2A, the pack reads 10V.

OK for some reason while discharging my battery just now, the charger brought it down to 8.5V while discharging at 2.2A (a damaging level for lipo cells?), I disconnected it and will await for diagnosis from someone here..wouldnt want to burn my house down.

Is there a bad cell in my pack? or is something else wrong. This pack isn't that old and hasn't been mis-treated. It seems weird that the voltage would remain at a nice level but the current would totally drop.

Also, when a pack says it is 11.1V, does this mean the cell voltage is 3.7 volts (3 cells in a pack, 11.1/3=3.7), because my charger had an option for 3.6 and 3.7 and I charge at 3.7 (hopefully I made the right choice).

Thanks

richrd

I’ll try to help but not enough imfo… First did the pack ever work right?? It only takes ONE oops and you can ruin a pack. BTW there are about 10 ways to oops a LiPO. First way to prove out a pack is charge 4.2V = to 12.6 V at 1C or less also with a BALANCER. “ Constant voltage will produce a current taper at 70%C to zero at end”. Discharge at 1C and check balance of each cell as it goes down I believe one or more are dropping way faster and at 9V typical stopping area at 1C I think one is below 2.5V and has gone bad. If so is over… cell must be discarded or better yet trash pack. This all assumes charger is working correctly.
Rich

[ShAdOw]-[HeLiX]

Yes the pack worked properly when I first got it, then I didn't use it for about a week and now when I try to charge it it doesn't work properly. I've got a computerized charger/discharger, so I can't select the specific voltage I want to charge it at - it brings the pack up to 12.6V using constant current, and then finishes the rest of the charge off using constant voltage and a changing current until it is 'full'.
The other battery I have is still working fine, so it's not the charger.
So as far as I can tell, one of my cells has gone bad spontaneously during a week where it wasn't in use.

I was wondering why it went bad? (do they sometimes just die for no apparent reason?), and can I do anything to fix it? - like a cell balancer or something of the sort.

Does a bad cell affect the voltage of the cell, or its current capacity, or both? My pack is still reading at a good 12.6V, it just can't hold enough current and I have no idea why (my charger tells me that it can put about 500mA into the pack before it won't accept any more, and it should be accepting around 2200mA). Also, if one of my cells has gone bad, does that mean that in a 2200mAh pack I should still be able to get around 1500mA into it (since 2 of the cells are still working)?

[ShAdOw]-[HeLiX]

Ok I just did a test with the battery connected to my multimeter. With no load, both batteries measure the same amount of volts (12.6), and the same amount of amps (3.3 ish..shouldn't this be 2.2A for a 2200mAh pack? :S). Well, once I connected the problem pack to my heli and powered it up (while holding the heli on to the ground), my battery monitor said all was fine until 3/4 throttle, where it reported the battery as low voltage/"stop immediately and recharge" - the same response I would expect from an exhausted normal pack. Once I lowered the throttle it was at 12.6V and 3.3A again. I did notice a considerable power difference between the two batteries.

Is this normal behavior for a pack with a bad cell?

richrd

Yes
Iam getting the impression you don’t balance or have a balance plug on your batteries. You need to monitor each battery to see which one is bad. If your batteries do not have a balancing connect make sure the next pack does and buy a balancer. Astro blinky is good enough and low cost. Lower than 3V in any cell when discharging is very very bad.
Warning some controller’s ESC go to low of LVC before they stop the motor. This will ruin most LiPO immediately just once below 3V in any cell and pack may be shot. I my self just time my flight so I stop with juice in battery. After I stop I want 3.5V per cell “10.5 all 3 cells” on my meter then long live the LiPO.
Rich