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Topic: 18650 charger that detects defective (overheating) cells (Read 135 times) previous topic - next topic

felic

Are there any good lithium lithium battery chargers that can detect defective cells.

I noticed that lots of old 18650 cells basically work fine, but if you charge them up to more than 4.1V they will get pretty hot and require much more time than usual to get to 4.2V.
I want to sort these kinds of cells out because when I use them in a project I use one of these charging board (e.g. one of these) and they always try to charge to 4.2V.

The chargers that I could find only show the internal resistance, which can be an indicator of a bad battery, but often isn't.

Another big problem that I currently have with a cheap charger is that one bad cell will heat up all the others so that everything is like 85°C and it becomes impossible for me to tell which one is bad.

raschemmel

Quote
Another big problem that I currently have with a cheap charger is that one bad cell will heat up all the others so that everything is like 85°C and it becomes impossible for me to tell which one is bad.
Traditionally before the advent of so many new devices, this situation would be dealt with by attaching
individual thermocouples to EACH battery. Today, the hobbyist can simply order 6 DS18B20 temperature
sensors, connect them all in on one bus. I have personnally bussed up to a dozen together and due to the
64-bit serial number there is no problem identifying which is which.

I strongly suggest you read the serial numbers individually by reading one at a time and then record them
and assign a sensor number (1-10) to them and write that on the top of the sensor by putting white out on the top and then when it's dry write a number 1-9 on it. Then you can look up the serial number and use
a case statement to send or display a message such as "#2 battery hot !"

These sensors are dirt cheap and despite the sophistication of the DS arduino library, even a non programmer like myself can use them.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

felic

Hm, but I'd have to attach them to the cells directly wouldn't I?
And in addition to that I'd have to heavily modify the charger adding relays for every cell.

And don't you think this would result in false-positives? I mean as I said the batteries seemed to share their temperature.
So once a cell reaches the temperature threshold and gets cut off, the other cells might be just one degree colder and still heat up by one degree to also get cut off.

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