Unbalanced lopo.

[Dvnts]

Hi everyone, I have noticed that one of my lipo's is not discharging evenly.
Its a standard 1800 mah that you get whith the t-rex. I use a balancer on every charge, and at the end of each charge the 3 cells are well balanced. The reading that I got on the last flight was as follows:

cell1. 3.58v
cell2. 3.55v
cell3. 3.37v

These readings are quite consistent and the 3rd cell is always lower. Would the battery be safe to use, there is no swelling or anything else wrong.

[Daz(DJLFlapper)]

the critical voltage for a lipo starts at the recomended 3volts, you can get away with going down to 2.5volts in anycell though this may reduce the life time of the battery. You showing a drop of .2volt I would not concidder this a problem to worry about unless you are intending to drop below 3Volts per cell. if any pack swells or get hot to the point it is hot to touch it has got to be treated as damaged and discarded.

I would not worry about it. As long as I had it ballanced and ready to use then the voltage stayed above 3V at the end of use I'd be happy.

[uneverno]

Hey there,
it doesn't look like much of an issue from where I sit. The cells just aren't particularly well matched, meaning that there is a variance in the charge/discharge rates of the cells. No two batteries are created equal, and the primary difference in the cost of battery packs is that the more expensive ones tend to be better matched. It takes time and therefore money for the manufacturer to do this.
When I was racing RC cars, I had several 100 $'s in matching equipment so I could build really well matched packs that discharged at the same rate. This was with NiCd's, but the principles are the same. Unfortunately, with LiPo's, building your own packs carries a high amount of inherent risk, so not recommended.
It sounds like you're following sound principles for care and feeding of your batteries. Keep an eye on it, but as long as the pack's balancing when you charge it, it shouldn't become a long term issue.

As an aside, if you don't have one, a programmable speed control will monitor your battery for you so that it can't be discharged too far.

[Daz(DJLFlapper)]

Some good advice given there. Just to point out the programable speed controller will actually drop the voltage to the motor when it reaches the level of voltage you choose. To give an example they have 3 choices. 1, 3.2 volts then it will decrease the power to prompt me to land. 2, 3.0 volts decrease to land. Then 2.8volts and cut the power to save battery.

they can save you the guess work of when the correct time to land is. Having said this it is always a good idea to time your flight and record your voltage drop. In this way you will be able to see if there is a problem with your lipo pack.

[Dvnts]

Thanks for the info guys, Just being cautious. I do have a programmable speed controller so the voltage should never get too low. Anyway I crashed on the weekend, so she is out of the air for a while.