Seems likely, with LiPos you want to avoid going below about 20% capacity. Not sure what that equates to per cell, something like 3.2v. I'd keep the pack in a charging bag at all times until a solution can be found (a roboteer buddy with a high end charger maybe) - likely to be answers online about how to resurrect. Of course, be wary of anything outrageous, LiPos are sensitive beasts.
Sorry but that lipo will be dead, from memory 2.8v per cell is minimum capacity I have my cut off set at 3v per cell,
So 6x2.8v 16.8v .this is not always dangerous but it will have damaged the battery capacity and current draw. The chargers won't charge below set voltage points because if you charge the lipo it is likely it will puff and be potential dangerous, my advice bin it safely and get a cutoff unit or a buzzer alarm at least whilst testing,
Just to point out we drained one of Binky's 5S lipos down to around 2.2v-2.5v per cell in 2013. With the Big Nipper teams Pro-Cell charger it was recovered and has been functioning fine ever since.
The consensus used to be that dropping the voltage on a lipo used to be its death but now it seems with a few more years of testing that it is massive current draws that do permanent damage. It was hard to spot this as it usually took a high current discharge (expected or unexpected) to drop the cell voltage that low. (This info comes from one of the New Scientists magazines regarding electric vehicles that use Lipos while comparing them to lithium Ion)
Keep hold of it and wait until you are at an event where someone will let you use one of the top of the line chargers. It may be dead but I reckon it can be saved.
Last edited by Eventorizon; 5th September 2014 at 13:40.
Yep, it was that pack, Alex, that I had in mind when saying a pro charger might be able to resurrect it. That and I accidentally ran my beetle's 3s down below our charger's threshold last year, and I forget how we did it (tricked the charger I think), but it restored fine and is now in the spinner. 2.2v per cell is extreme and may be beyond rescue but there's nothing wrong with trying to (safely) restore it.
As long as none of the cells have completely died, its possible to recover the battery by giving it a partial charge to bring the voltage up to a point where the Lipo charging program recognises the pack as having 6 cells. The best thing to use is a current limited bench power supply but as they are rare, you can use the Imax charger in it's Pb (lead-acid) mode.
* Set the charger to an 18V Pb battery and low charging current, 0.5A or less. Don't connect the balancing cable at this point. The charger should accept the pack as a
* When the charge current drops down to almost nothing or the charger finishes its cycle, the battery should be charged up to around 18V.
* Disconnect the battery and check the voltage. Wait around 15 minutes and check again; if the voltage is the same or only a little lower, the pack is savable, if the voltage is heading back to 14V, its dead.
* Assuming the pack holds its voltage, set the charger for a 24V PB battery and start charging again. You don't want to complete this charge cycle, you just need to raise the battery voltage to around 20V so that the lipo program recognises the pack. Charge for 15 minutes, check the battery voltage and repeat until the pack holds around 20 to 21V.
* Set the charger to the Lipo mode, connect the balance cable, set the current down low and try charging. If the charger still indicates low voltage, try more time on the Pb charge mode. If the charger accepts the pack, monitor the individual cells by pressing the DEC button (described on page 30 of the manual). If any of the cells are wildly different voltages, you probably need to switch over to balance charging.
To stay safe, do all this outside on a non-flammable surface. I have brought back several packs this way and while they may have balancing problems or a shorter life span, its worth trying.
Hi guys,
Tried what Nick suggested today, got the voltage up to 18v but wouldnt go any higher than that on Pb mode and wouldnt recognise the battery on LiPo mode... I'll try again tomorrow, failing that I might need to borrow a proper charger at the uk champs.
A 'proper' charger might not do any better - all Lipo chargers have safeguards to prevent you charging a pack to the wrong voltage. If your pack's voltage is still outside the range of a normal 6S pack, then all chargers should reject it. It could be that one cell has completely given up and you can test that by measuring the voltages on the balance cable.
There should be a black wire on one end of the balance cable and that is the negative connection. All the other balance wires go to the positive side of each cell and you can measure the voltage of each cell by placing one multimeter probe on the black balance wire and stepping the other probe along the connector. If all the cells are OK, the voltage will step up by about 3V as you measure across successive wires. If the voltage steps up significantly less than 3V at some point, that's a dead cell.
What I did to revive a recently over discharged pack was to partly charge it with a bench supply. I set the voltage to 22V and the current limit to .5A and got the pack voltage up to a point where the Lipo charger could balance the cells. The good thing about a bench supply is that it has no safeguards and just does what you tell it; as long as you treat the Lipo with respect and monitor its temperature, using a bench supply should be quite a safe way to revive a pack.
Btw, what's the bit in brackets in the title meant to mean
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