Protected Sanyo UR18650ZT got super hot while charging. Thoughts?

Batteries and Chargers Rechargeable Batteries
1

I just received a shipment of protected Sanyo UR18650ZT 2800 mAh 4.3v cells from Fasttech today and was charging one up on my Thunder AC680 hobby charger. I was charging it at .5C and 1S (1.3A, 3.7v) and after about an hour or so, I touched the battery and it was almost too hot to touch. I immediately stopped charging it and set it on the floor with a trashcan on top in case it decided to blow up.

I am genuinely curious why this happened. When I started charging it, it was at 3.68v per my Extech EX320 DMM. When I took it off the charger, the AC680 readout showed it was charging it at .8A and the cell was at 4.20v. Now that I check the voltage again with my DMM, it is at 4.09v.

Did I do something wrong? I was under the impression a standard charger would just charge these up to 4.2v and stop there and for all intents and purposes, it would just charge up to about 2600mAh and have a little headroom so the cells wouldnt wear down as quickly.

Any insight would be appreciated.

2

I’m anything but an expert but my Icharger does not charge at .8 amps at 4.2 volts. This sounds fairly high to me.

3

Mine can do up to 6 amps at 4.2v. The Intellicharger i4 does 750mA. .8Amps isnt that much.

4

I would suspect you have a bad cell.

I don’t charge over 1A, but a li-ion will stay cool at that level, and I would be very concerned about the health of any cell that got noticeably warm to the touch.

It doesn’t sound like you are at fault. Several factors can damage a cell in transit or storage. Charge a couple of the others and see what you find, but if any start to get warm discontinue what you are doing and double check your settings. You can test check the amperage output of your charger, but it’s likely not an issue.

FastTech will replace any bad cells under warranty.

5

The chargers are supposed to start lowering charge current as the battery approaches 4.2v

Sounds like yours was not.

6

Pitch the cell. Too hot to touch would suggest an internal issue.

7

I’m by no means an expert on the subject, but both my hobby chargers start lowering the current once at 4.2v, but provide a constant current when on the approach. I was under the impression that this is correct for the CC/CV charging system.

8

I bought 10 unprotected Sanyo UR18650ZT’s from Fasttech in February & had one cell overheat. On the first (and only!) charge it hit 138F and was still rising when I stopped the charge. Fasttech replaced the cell and the replacement was fine.

9

Well I guess it depends on the charger. My Intellicharger seems to lower current the closer to full the battery gets.

10

Can you check internal resistance with that charger? The current measurements you mentioned seems correct. Did the charge tell you how much charge was input into the cell?

11

I didnt notice before I shut it off. I have it set to stop at 5000 though.

I charged the rest of them on my Intellicharger i4. They all charged up with no problems.

I am going to contact Fasttech about a replacement.