Lipo charging, an unforseen danger

[Andy48]

Came across something really scary today. I have several chargers and was duly charging some batteries. Each charger has a monitor showing the individual cell voltage. One 5S battery was showing one cell a few tenths of a volt lower than the rest which was puzzling. Normally they are quite close, and I always balance charge them. It was OK last time I charged it.

I was with them in the workshop, and checked up on them 20 minutes later. This battery was now showing the same cell nearly a volt lower! I switched off the charger and checked the balance lead and its connections to the charger. When I switched on again, the other 4 cells showed 3.95 volts and this cell showed 4.22 volts. The charger had sensed the lower voltage from this cell and had duly tried to charge this one up first into line with the other cells. In reality it was overcharging one cell, and had I left them or not noticed it, it could have resulted in a fire.

Had it actually caught fire, I would never have been the wiser as to what happened.

As the safety warnings say, never leave lipos charging unattended, and I'd also add keep a regular check of each cell voltage as they charge.

Edited By Andy48 on 08/06/2020 17:57:12

[Allan Bennett]

What make/model charger was that? There's certainly something wrong with it, for even if there had been a problem with the leads it should have stopped the charge before letting things go so far.

[Trevor]

Sounds like a balance connection problem to me. Could be internal to the charger, the connector on the charger, ditto on the balance board if you are using one, or internal to the battery. It sounds like when you re-seated the connector the charger was able to read the cell voltages correctly. Until you did that, it wouldn’t have known it was overcharging the cell.

So, if you are using an external balance board, I’d replace it. If you are connecting the balance lead directly to the charger, then it’s time to buy an external balance board! Either way, I doubt there’s a problem with the charger itself.

Trevor

[Jesus Cardin]

All Li-Po balance chargers I know do not overcharge the lower volt cell but "brake" those which go ahead.

As far as I know and understand Li-Po chargers these put an electronic resistence to the higher voltage cells till those with lower ones cachts up.

Anyway the problem suffered certainly seems to be from a bad contact on the balance line.

[Andy48]

Posted by Allan Bennett on 08/06/2020 20:20:11:

What make/model charger was that? There's certainly something wrong with it, for even if there had been a problem with the leads it should have stopped the charge before letting things go so far.

No. Nothing wrong with the charger. It was a connection problem in the balance lead, so the charger never saw the correct voltage.

This could happen to any make of charger.

[Andy48]

Posted by Jesus Cardin on 08/06/2020 21:21:20:

All Li-Po balance chargers I know do not overcharge the lower volt cell but "brake" those which go ahead.

As far as I know and understand Li-Po chargers these put an electronic resistence to the higher voltage cells till those with lower ones cachts up.

Anyway the problem suffered certainly seems to be from a bad contact on the balance line.

You have completely missed the point. The charger did not see the correct voltage so could not put a brake on the high voltage cell.