Is lipo too unbalanced or do I just need a better balance charger?

[ambientvoid]

I have a lipo which has been in storage and unused for a few years and having checked it recently the cells are sitting at 3.79, 3.79, 4.10 and 4.10. I have tried balance charging it before discharging it back to approximately storage voltage and it doesn't seem to have made a difference to how far out the 2 pairs of cells are from each other.

Am I better off just binning the lipo and getting a new one?

The lipo is a 4s 10000mah 10c Turnigy Multistar and the charger is a Turnigy Reaktor 250w 10a

 

[amberwolf]

As cells age they become different in characteristics (capacity, internal resistance, etc), even when originally well-matched (which is almost certainly never the case in RC LiPo packs).

So the cells you have there have likely become significantly different; you can test to see which are lower capacity / higher Ri / etc but since you can't fix it (other than by replacing cells), it'd be simpler and probably more cost-effective to just replace the pack as a whole (and save this one for testing stuff, etc., since it probably still works but at lower current-delivery capability, and lower capacity).

 

[eMark]

it'd be simpler and probably more cost-effective to just replace the pack as a whole (and save this one for testing stuff, etc., since it probably still works but at lower current-delivery capability, and lower capacity).

Any further "testing stuff, etc" could result in dire consequences proceed with CAUTION !

I have tried balance charging it before discharging it back to approximately storage voltage and it doesn't seem to have made a difference to how far out the 2 pairs of cells are from each other

What was voltage of each of the 4 cells when put in storage for past few years? __________
What was voltage of each cell after storage before attempt to balance charge? __________
Problem more likely two weaker cells (3.79V) - not - getting a "better" RC Hobby Charger ?

The only way to really know the condition of the cells is to first discharge the two cells that are at 4.10V to 3.79V. First try charging (outdoors) the equalized pack to 3.90V (bulk charge not balance charge). If the two weaker cells are again lagging behind (e.g. 3.85V) best to completely discharge the pack and discard.

 

[ambientvoid]

I think it was stored at around 3.9v per cell, when I checked recently 2 cells were around 3.85 and 2 were around 3.70 so if anything it seems they got a little further apart during charging. If I do have to dispose of the pack is 3.3v a sufficient point to discharge it to or should I try to drain it all the way down to 0v?

 

[neptronix]

Voltage differences like these indicate some cells have significantly higher self discharge, or at least a sizeable difference in storage capacity.

Would recommend fully charging them, then discharging them to about 3.7v-3.8v average and checking to see if the capacity difference is significantly large, so you can find out the safety margin on those.

 

[eMark]

Would recommend fully charging them, then discharging them to about 3.7v-3.8v average and checking to see if the capacity difference is significantly large, so you can find out the safety margin on those.

He has already tried FULLY charging with his RC Hobby Balance Charger. Two of the cells of his 4S Lipo that were at 3.85V (after few yrs in storage) were charged to at least 4.10V. While the other two cells that were at 3.70V of his 4S Lipo only charged to 3.79V. This suggests that he didn't store the pack at/near nominal voltage, but possibly closer to 4.00V. Thus the apparent self-discharge of 3.85V with two of the cells and 3.70V with the other two cells. This was before he tried charging his 4S Lipo to 4.10V (16.4V) with his RC Balance Charger.

The voltage increase in the two better cells increased by 0.25V (3.85V to 4.10V)
The voltage increase in the two lesser cells increased by 0.09V (3.70V to 3.79V)

If the above voltages are correct from what he's stated in previous posts then that 4S Lipo has likely suffered damaged beyond repair. The best way to know if those two weaker cells can be rejuvenated (doubtful) is to discharge the two 4.10V cells to the current voltage of the two lesser cells. Then with the 4 cells equalized (voltage wise) try first charging the pack to 15.6V (3.90V/cell). My guess is that there will again be a disparity. The 2 better cells ... say around 3.95V while the other two lesser around 3.85V (7.90V+7.70V=15.6V)

If by chance the 4 cells are each at 3.90V (15.6V) then and only then try charging your 4S Lipo to 16.0V. Then if all 4 cells are at 4.00V try charging to 16.4V. Then if all 4 cells are each at 4.10V you may want to try FULLY charging if the pack isn't puffed/swelled or gets warm while charging at either 1.0amp or 1.5amp rate. Suggest you do any further charging outdoors ... just in case . If the above progression isn't possible with two of the cells always lagging behind ... then discharge and discard your 4S Lipo as it's not usable as is.

Bulk charge (1.0amp or 1.5amp rate) when using your RC Hobby Charger. It's not out of the possibility that there's a problem when Balance Charging. More likely 2 of the lesser cells are beyond rejuvenating. What's a little perplexing is why two of the cells are exactly the same at 4.10V, while the other two are exactly the same at 3.79V. Suggests that two of the cells were A grade, while the other two cells were B grade.

 

[eMark]

The bottom photo shows a couple ways you could try to discharge the two higher voltage cells (4.10V) to same voltage as the two lesser cells (3.79V). Using a 12V bulb soldered to doorbell wire with 1/8" bare wire to insert into your JST-XH connector. Then bulk charge your 4S Lipo to 15.6V. Hopefully all four cells will be at 3.90V. If not you could try discharging the two higher cells so all are again at the same voltage and try bulk charging to 16.4V. If all 4 cells still aren't the same voltage (4.10V) then time to completely discharge and discard.

The JST-XH patch cable w/Deans connector can be used for charging an individual cell with RC Hobby Charger set at 1S using either 1amp or 1.5amp charge rate. Can also be used to discharge an individual cell of a RC Lipo battery by connecting to that other 12V bulb with the Deans connector.