All my lipos are dead!

[Guest]

Key is not to store them and keep flying

Joking aside that's a real shame especially trying to off load a heli you really like because of it.

MJ

[hanson]

My thoughts as to what could have happened.

if the lipos were parallel discharged to storage charge, it would only need one balance wire/extension/dodgy connection, to corrupt/damage every pack. I've seen this myself and damaged several packs that I thought were parallel charging fine, because the charger said so. This was on a powerlab and the revolectrix board. I now only connect one packs balance connector when parallel charging and monitor the others with a volt checker. If they were not parallel charged/discharged then I would guess it's a lack of regular use.

[Grumpy]

I now only connect one packs balance connector when parallel charging and monitor the others with a volt checker.

Only problem there is that the packs that don't have their balance wire connected wont balance.

[hanson]

Only problem there is that the packs that don't have their balance wire connected wont balance.

thats sort of the point, they also won't balance incorrectly and damage all the packs

[mahbouni]

Even if you storage charge all cells to exactly 3.85V, they will sag by different amounts over time. If doesn't matter if one cell is at 3.82V and the other is at 3.84V. It's more important that when you fly your model all the cells are balanced, otherwise some cells will be working harder than others and they will age more differently.

[Grumpy]

Agreed, balancing at storage isn't important.. I was talking about balancing when fully charging.

Without balance leads connected on all the packs a battery could go for several charge cycles without being balanced, which obviously is likely to result in the cells becoming unbalanced.

[mahbouni]

Or the more extreme case of one cell is much weaker than the others and charges much quicker than the rest. By the time it reaches 4.2V the other cells might only be at 4.0V but the charger sees only the total voltage. So for a 6s pack, by the time you reach termination voltage of 25.2V, your good cells might be at 4.17V but your weaker cell could be at 4.37V, which would be dangerous.

[hanson]

Or the more extreme case of one cell is much weaker than the others and charges much quicker than the rest. By the time it reaches 4.2V the other cells might only be at 4.0V but the charger sees only the total voltage. So for a 6s pack, by the time you reach termination voltage of 25.2V, your good cells might be at 4.17V but your weaker cell could be at 4.37V, which would be dangerous.

This was kind of what I was trying to get at, although probably poorly explained. If you use your example and apply it to a parallel charge situation, suddenly cell 1 for example on one bad pack or dodgy connection won't go past 4v for example, the other cell 1's on the other 5 packs connected in parallel using the balance leads go past 4.20 to compensate and end up damaged. By only connecting 1 balance lead and monitoring the others with a volt checker you can get around this.

Now you have six damaged packs, but the charger shows everything as fine, because it just show the parallel voltage

[hedge]

Wow! Well, I've not been able to get out flying this year. My lipos were all on 40% storage charge in an ammo box, I came to charge up this morning only to find all 8 have puffed out like barrels and look fit to burst!

Needless to day I can't use them, HK no longer do these cheap lipos anymore (after this I'm not sure I'd trust them anyway) and the more expensive ones are too pricey for me!

Anyone else had lipos puff out after being on storage charge?

I feel for you I really do. I had two of these blues go in my early adventures into e flight. Back then they where about 45 each so no biggie but now they are getting more expensive this is not a cheap fix. People say N is expensive but you just don't wake up with an £800 bill for no good reason. If your brave enough you might be able to make 6 good packs by soldering in good cells from the puffed packs? I know my skills aren't up to it but I have heard some have success adding and removing cells.

[mahbouni]

This was kind of what I was trying to get at, although probably poorly explained. If you use your example and apply it to a parallel charge situation, suddenly cell 1 for example on one bad pack or dodgy connection won't go past 4v for example, the other cell 1's on the other 5 packs connected in parallel using the balance leads go past 4.20 to compensate and end up damaged. By only connecting 1 balance lead and monitoring the others with a volt checker you can get around this.

Now you have six damaged packs, but the charger shows everything as fine, because it just show the parallel voltage

I think if you balance charge 2 or more cells in parallel, and one bad cell will not go past say 4V, then the other ones will keep going as normal. The charger sees it as 1 cell and the only way it can know there is a problem is if it detects an abnormal increase in resistance. The bad cell that won't go past 4V will have a higher resistance than the others. If you have only 2 cells in parallel then it would be very obvious if you detect that one cell in the pack has double the resistance of the others, but if you have 6 packs in parallel then the difference might not be so obvious to the charger.

Another scenario is if your parallel balance connector has a faulty wire/pin, effectively not balancing one of the cells. It would still be connected to the good cell that is in parallel with it so wouldn't notice any loss of connection. Only the resistance would increase of that combined set of cells that are in parallel. Again, if you have only 2 packs in parallel then it might detect the situation quickly, but if you have 6 in parallel then would it?

[horneteer]

These days when I fly my 700 electric, I just take my 2 oldest packs to the field and charge them @5C with my PL8 hooked up to 2 deep cycle batteries in series. The packs charge in about 10 minutes. This is much better than buying, maintaining and charging lots of packs at home. Reduced fire risk as well. I can have between 0 and about 16 flights without pre-planning or fannying around with multiple packs.

Since OP has a decent charger you might want to do the same now that yours are toast.

[hanson]

I think if you balance charge 2 or more cells in parallel, and one bad cell will not go past say 4V, then the other ones will keep going as normal. The charger sees it as 1 cell and the only way it can know there is a problem is if it detects an abnormal increase in resistance. The bad cell that won't go past 4V will have a higher resistance than the others. If you have only 2 cells in parallel then it would be very obvious if you detect that one cell in the pack has double the resistance of the others, but if you have 6 packs in parallel then the difference might not be so obvious to the charger.

Another scenario is if your parallel balance connector has a faulty wire/pin, effectively not balancing one of the cells. It would still be connected to the good cell that is in parallel with it so wouldn't notice any loss of connection. Only the resistance would increase of that combined set of cells that are in parallel. Again, if you have only 2 packs in parallel then it might detect the situation quickly, but if you have 6 in parallel then would it?

so in your first scenario, 1 pack cell 1 won't go past 4v, 2nd pack goes to 4.4v because the charger see's 4.20v as an average of the 2, now 2 damaged packs. Charger thinks all is ok and the user is none the wiser.

[mahbouni]

so in your first scenario, 1 pack cell 1 won't go past 4v, 2nd pack goes to 4.4v because the charger see's 4.20v as an average of the 2, now 2 damaged packs. Charger thinks all is ok and the user is none the wiser.

Lets first assume you have 2 perfectly good cells; one is charged to 4V and the other is charged to 4.2V. If you connect them in parallel then the one at 4.2V will charge the one at 4V until they both reach the same voltage of 4.1V. Electric charge is like water and finds it's own level. But it doesn't happen instantly. It takes time.

Now lets assume that the one at 4V is damaged and won't charge past 4V. The one at 4.2V can not charge it because it is putting up too much resistance. To discharge a cell you need to allow current to flow and if it can't flow then you can't discharge it. Hence, if you measure the voltage across both these cells at the instant they are connected in parallel then you will still see the same Voltage of 4.2V across both of them. Your charger does not see averages.

[hanson]

Lets first assume you have 2 perfectly good cells; one is charged to 4V and the other is charged to 4.2V. If you connect them in parallel then the one at 4.2V will charge the one at 4V until they both reach the same voltage of 4.1V. Electric charge is like water and finds it's own level. But it doesn't happen instantly. It takes time.

Now lets assume that the one at 4V is damaged and won't charge past 4V. The one at 4.2V can not charge it because it is putting up too much resistance. To discharge a cell you need to allow current to flow and if it can't flow then you can't discharge it. Hence, if you measure the voltage across both these cells at the instant they are connected in parallel then you will still see the same Voltage of 4.2V across both of them. Your charger does not see averages.

So you're saying that your charger only shows the higher voltage? E.g. 4.20v?

i don't know about your charger but mine shows the average of the two cell voltages. I just tested to check, I connected one pack with cell 6 showing 4.14v and 1 with cell 6 showing 3.84v, the charger then showed cell 6 at around 3.96v, with your theory it would have shown 4.14v, take the higher v pack back off the charger and voltage is back up to 4.13v. This means that with a dodgy cell/board/connector my charger can potentially keep charging cells that have already hit 4.2v because the lower cell brings the average voltage down.

just trying to help the op with a possible explanation as to what could have happened to his packs, something that happened to a set of my packs and what I have done to try and prevent a future problem. Yes it requires looking at pack balances occasionally, but having wasted a set of packs, I prefer that to parallel balancing.

[Grumpy]

so in your first scenario, 1 pack cell 1 won't go past 4v, 2nd pack goes to 4.4v because the charger see's 4.20v as an average of the 2, now 2 damaged packs. Charger thinks all is ok and the user is none the wiser.

The cells are connected together in parallel. It's pretty much impossible for one to be at a higher charge state than the other as they are directly connected. If one was higher then current would flow from the high cell to the low cell until they became even (doesnt take long). That's why it's important that you have the balance leads connected.

There are some risks in parallel charging. The biggest is probably the scenario that one cell develops an internal short which would cause all the other cells to discharge into it, possibly causing the failed cell to burst. To make this less likely just make sure that your batteries are in decent condition and none have cells that are showing signs of failing. The charger should pick up if it were happening but you would have to be there to disconnect the batteries. This would be a problem even if you dont have the balance leads connected because the good batteries would drain into the bad one via the main power cable, but in that case the charger is unlikely to detect the problem.. Yet another reason to always connect all the balance wires!