Charger overcharging one cell?

[Xanda2260]

Hey guys, got some weirdness going on with my lipo. Got 6 x 6s packs, wired for 18s2p. Charging to 4.1v and cell 2 is coing out high (about 30mv). When pack has been sat a week or two, cell 2 is still at 4.13, others have dipped to 4.08ish.
I'm thinkin the cheap-ass charger is miss-calibrated on cell 2, but is there any other likely issue that could cause this?

Cheers guys

Alex

 

[neptronix]

Cheap chargers will do that. Some come wildly miscalibrated. They should be called cell disblaancers

Just to be sure, are you charging in balance mode and making this measurement after the charge has completed ( as determined by the charger ) ?

 

[Xanda2260]

Cheap chargers will do that. Some come wildly miscalibrated. They should be called cell disblaancers

Just to be sure, are you charging in balance mode and making this measurement after the charge has completed ( as determined by the charger ) ?

Yep, and with both a battery medic and a fluke. As long as its just the crappy charger, im not that bothered. Just didnt want to assume anyhing with lipo.

Cheers nep

 

[neptronix]

You can't rely on a battery medic to do a good job of measuring or balancing either. At least you have a fluke though

Might want to upgrade your charging equipment. 100mV of difference will definitely cause a lipo battery to wear poorly over a long period of time. The 4.1v-4.15v cells will outlast the 4.2v cell.

It will also cause significant differences in voltage as you cross over the 3.6v/cell average mark during discharge. You then have to cut the pack off early to avoid damage from some cells becoming overdischarged. That's the worst part.

 

[cwah]

My pack is also getting disbalanced very quickly.

The only solution is the battery medic?

 

[Xanda2260]

Oky doke, all cells balanced using medic. Fluke confirms + -10mv. I'll run normal charges and see how well balance holds up. If I have to use the medic after each balance charge its not too bad. Providing the cells don't wander too quickly. Don't discharge below 3.6 per cell so hopefully it'll be ok...
Cheers guys

Sent using the might of the Android Army!

 

[Xanda2260]

Update! I haven't balanced since last post. Done about 10 normal charges and balance is still holding at + - 10mv. Awesome!

Cells charged to 4.1v and deepest discharge so far was about 3.8.

Sent using the might of the Android Army!

 

[dogman dan]

To get a pack truly balanced, charge each cell one by one with the 1s setting of the charger. It might be off, but all cells will be off the same now.

I use a pair of bare male jst leads to plug into the balance plug on a single cell, then charge at 1s 1 amp. Charge the whole pack to nearly done first of course.

 

[Xanda2260]

Cheers dogman, thats a cool tip. Think I'll give that a go this half term.

Thanks

Alex

 

[Skippic]

I had a similar issue. After disassembling the charger I found one resistor was not soldered correctly.

 

[Xanda2260]

Mmm, I may have to have a look-see.

Cheers