New 2S Reedy LiPo out of balance

[Toon]

A few days ago, I bought a Reedy AS309 7000mAh 65C 7.4V 2S LiPo (from MB Models http://www.rccarshop.co.uk/index.php...v-2s-lipo.html). Friday night is my local club race night, and I have just got back from using the LiPo for the first time. The problem is, the cells won't balance. I always balance charge, and charged the pack at 6.0A (which is the highest my charger will do), but 1 cell charges to 4.2V, but the other cell won't go above 4.0V. The charger ends up just constantly varying the charge rate up and down between 0 and 0.5A, but the cells won't balance. I thought the cell voltages might even out through use, but after 4 charge/discharge cycles (through racing), the imbalance is still there.

Has anyone had experience of this kind of issue? Would it be worth trying a storage voltage discharge, then a slow balance charge at 0.5-1.0A to see if the cells balance out? Or, as the LiPo is brand new, shall I just contact MB and try and get it replaced?

Cheers

[Craig W]

Originally Posted by Toon

A few days ago, I bought a Reedy AS309 7000mAh 65C 7.4V 2S LiPo (from MB Models http://www.rccarshop.co.uk/index.php...v-2s-lipo.html). Friday night is my local club race night, and I have just got back from using the LiPo for the first time. The problem is, the cells won't balance. I always balance charge, and charged the pack at 6.0A (which is the highest my charger will do), but 1 cell charges to 4.2V, but the other cell won't go above 4.0V. The charger ends up just constantly varying the charge rate up and down between 0 and 0.5A, but the cells won't balance. I thought the cell voltages might even out through use, but after 4 charge/discharge cycles (through racing), the imbalance is still there.

Has anyone had experience of this kind of issue? Would it be worth trying a storage voltage discharge, then a slow balance charge at 0.5-1.0A to see if the cells balance out? Or, as the LiPo is brand new, shall I just contact MB and try and get it replaced?

Cheers

if you know some1 with true 20 or 30amp discharger after race take 1000 to 1500mah out let them cool then try balancing them if that does not work return them

[JonyNitro]

Give it time it's a new battery plus what charger you got,plus balance charging every charge is just anal, 4.00 4.20 is a lot,ask some else with another charger,

[sosidge]

More charges just means more risk. If it won't balance, it means that one of the cells in there is out of spec. I'd try it on a different charger - once - to make sure it isn't a charger falt, and then I'd return it.

Funnily enough a racing buddy has gone through two brand-new HPI Plazma packs in the past couple of weeks with the exact same problem, neither would balance despite being tried on several chargers.

[Toon]

I contacted MB Models, and they recommended trying discharging the LiPo, then doing a balance charge, and letting it continue to try and equalise the cell voltages, though it may take several hours to do this.

So, I used the storage mode function on the charger to take each cell down to 3.7-3.8V, then did a balance charge. As before, one cell reached 4.2V and the other cell was still at 4.0V, but I just let it continue charging, checking it periodically to see if the voltage was coming up on the lower cell. The charge current fluctuated between 0-0.3A, but slowly the voltage did come up. It took about 5-6 hours, but eventually both cells were at 4.2V, even though the charge didn't peak and cutoff.

I have since tried discharging 1000mAh from the pack, then another balance charge, and it went fine, each cell reached 4.2V and the charge peaked and cutoff. It appears fine now, and hopefully now that the cells are balanced, they will stay balanced!

[Matt Butcher]

Handy to know! Thanks for posting how it was sorted