How do chargers sense battery temperature

I've poked around a little, but have not found anything. Sorry if I've missd this.

How to consumer chargers determine the battery temperature? It seems like it must be through the same contacts that are being used for the power transmission.

Probably with a thermistor mounted underneath and near the battery cradle

electrolyte said:

I've poked around a little, but have not found anything. Sorry if I've missd this.

How to consumer chargers determine the battery temperature? It seems like it must be through the same contacts that are being used for the power transmission.

Click to expand...

With a thermistor placed close to the battery, on this charger it is very obvious where it is placed:

In practical terms the thermistor is configured to be one half of a resistive voltage divider.
A normal resistor typically doesn't vary its resistance much when it's temperature changes, unlike a thermistor which is designed to have large resistance changes when the temperature changes.

The microcontroller inside the charger uses an analog-to-digital (ADC) input to read the voltage drop across the thermistor. So as the battery heats up, the thermistor gets warmer and the voltage drop across the thermistor rises (or falls, depending on what type of thermistor it is, both types exist).

Thanks for your kind responses, both low and high technical electronics levels :thumbsup: I really don't have more than one good charger to look at closely (Nitecore D4). I've been reading the wonderful reviews here and my curiosity about temperature sensing was piqued, but the pics don't help me see how temp sensing might work. I asked because it seemed to me that a sensor that requires contact for conductive heat transfer would be difficult to pull off in a reliable way on a cell stuck sideways into one of these chargers. I'd be looking for a compressable, conductive pad of some sort unless primary heat transfer from battery to the charger element is radiative. That is a whole nother can of worms.

I continue to think that sensing through the electrical contacts should work, but there is probably a pit-fall that I am not considering.

There are other difficulties with the temp sensing control that I am curious about. Has anyone ever put a charger in an idle refrigerator or other warm box, started the charger and then cooled the environment down to see what happens?

Sorry for my slow response with thanks. I am relatively new here. Before I sleep again, I have to look to see if my account is configured for email notification with responses. I thought it was.

One way to make good contact is to place a spring behind the metal pads, Xtar do that on the above charger.
Most chargers do not, this means less precise temperature reading, but usual good enough for the purpose.

Thanks very much and thanks for your detailed reviews.