All my lipos are dead!

[mahbouni]

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.

The cell with the higher voltage is dropping voltage under load because it is charging the cell with the lower voltage. If you quickly remove the load then it's voltage goes back up, but if you leave it for a long time it won't. Assuming both cells have identical internal resistance then the voltage drop will be exactly half of the difference between them. If the cell with the lower voltage has double the internal resistance then the voltage drop will be a quarter of the difference.

However, when you are charging the cells, you are forcing current in the opposite direction, so the cell with the higher voltage is gaining voltage.

[hanson]

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!

Unfortunately it it is possible as I've tried to describe. Charge how you feel best.

ultimately, the op's battery's are toast. Moving forward I liked the idea of fast charging at the field. 1 set of packs or 2sets of packs and a duo, if you can't bring yourself to 5c your packs. And fly all day long on £90-180 a year depending if you go with 1 or 2 sets of packs

[hanson]

The cell with the higher voltage is dropping voltage under load because it is charging the cell with the lower voltage. If you quickly remove the load then it's voltage goes back up, but if you leave it for a long time it won't. Assuming both cells have identical internal resistance then the voltage drop will be exactly half of the difference between them. If the cell with the lower voltage has double the internal resistance then the voltage drop will be a quarter of the difference.

that wasn't the point, the point was my charger sees the average of the 2 cells. Anyway, moving on ��

[Grumpy]

Unfortunately it it is possible as I've tried to describe.

I dont want to labour the point but I wonder how you think that two or more different voltage cells can be connected together in parallel and remain at different voltages for but a few minutes? For sure I've been parallel charging up to 16 batteries at a time every weekend for years and have never observed this phenomenon, nor can I see how it theoretically could ever happen?

Charging in the field is a great option 'if' you have the facilities to do it.

[hanson]

I dont want to labour the point but I wonder how you think that two or more different voltage cells can be connected together in parallel and remain at different voltages for but a few minutes? For sure I've been parallel charging up to 16 batteries at a time every weekend for years and have never observed this phenomenon, nor can I see how it theoretically could ever happen?

Charging in the field is a great option 'if' you have the facilities to do it.

clearly you do. I think it, because I've seen it. On my set up with my packs. I'm not doubting your experience in charging batteries, but you seem to be doubting mine. Take the example of a faulty cell that doesn't go past 4v in one cell, no matter how much the parallel cell wants to equal it to its voltage. The charger sees the average of the two voltages, what happens next?

[mahbouni]

that wasn't the point, the point was my charger sees the average of the 2 cells. Anyway, moving on ��

No, your test is based on 2 good cells of similar IR. In the scenario you described previously where one cell is damaged and can't be charged above 4V, it wouldn't allow current to flow through it, so your good cell would not drop under load. It would be as if you replaced the bad cell with a resistor of massively high resistance.

[Grumpy]

Take the example of a faulty cell that doesn't go past 4v in one cell, no matter how much the parallel cell wants to equal it to its voltage.

What would happen there is that the other parallel connected cells would drain into the faulty one until they all went down to 4V.

It comes down to the basic fact that current will always flow from the high voltage to low voltage until the voltages are equal.. it's impossible for it to be any other way... You cannae change the laws of physics Jim

[hanson]

What would happen there is that the other parallel connected cells would drain into the faulty one until they all went down to 4V.

It comes down to the basic fact that current will always flow from the high voltage to low voltage until the voltages are equal.. it's impossible for it to be any other way... You cannae change the laws of physics Jim

thats not what mahbouni is describing, maybe you're both right �� My physics is not that great to be honest. So I'll gladly duck out of this one. Just speaking from experience. Faulty cells/parallel board/balance extensions. Who knows. The only thing I know is that for I will happily parallel charge but only balance one pack, in my mind it's the better way.

[gazmk2]

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.

I actually flew them to discharge and them charged back up to 40%. Weirdly some of them have returned back to their normal size after a couple of days in the garden! I wouldn't use them still but the whole thinmg has n=me baffled, but also very thankful they didn't puff right out and cause a fire. In 6 years of using lipos i've never had this!