3 cell Lipo Questions

[atstodd]

Hi All,

I have a Flightmax 5000mAh 3S1P lipo that i bought about 6-7 months ago. It sat in its box till about 2 months ago when i decided to balance charge it in anticipation of finishing my bicycle light. It took FOREVER to balance charge. about 10 hours maybe more. I would charge it for about 2 hours a day when i had the time to monitor it. One of the cells was a few tenths of a volt lower than the other two but slowly came up. The charger is a Turnigy Accucel-6.

I finished my light tonight and took it for a test ride of a little over an hour. Its a single SSC P7 emmitter running at about 2.8A. Before the ride the battery voltage was 12.05V and after it was 11.69V. I decided to measure each cell to check the balance and got 3.97, 3.96, and 3.75.

The 3.75 worries me a bit, but I have almost no experience with Lipos. Is this bad or normal?

 

[Robin24k]

That is definately not normal, having a weaker cell is definately a dangerous situation should it have been discharged more.

Try charging the battery and record the off-charger voltage (make sure they are all the same). Let it sit for a couple days and see what the voltages are like.

 

[atstodd]

I will charge it up again. I should wait about 30min to check the voltage after charging correct? Also this battery is rated at 15C so I am not really stressing it at all as far as discharge rate. Does that matter?

Thanks!

 

[Robin24k]

I would give it a day or two, it's not likely to show much difference within 30 mins.

You should be fine, lithium-based batteries are capable of delivering high currents without issue.

 

[atstodd]

Looks like some of the posts were lost. Anyway, I removed the bad cell after one of you mentioned the balance charge was taking too long. Now I have an 8.4v lipo that should run for a little over 3 hours. What should I do with the bad cell?

 

[Robin24k]

Recycle or toss it.

 

[znarfcram]

Actually, there is an easy and safe way to neutralize the battery (or cell in your case) for disposal in regular garbage. Unlike most other batteries they are evironmentally safe .

http://www.rctoys.com/pr/2007/07/06/safely-dispose-of-lithium-polymer-lipo-lipoly-battery-packs/

Basically, the long and short of it is you should preferably start with a discharged battery and submerse it in a plastic container (with lid) filled with a salt water mixture (1/2 cup salt per 1 gallon water) for at least 2 weeks. Then its good to go.