Not car related - TomTom 825 won't charge

[Captain Jack]

Hi,

My girlfriend's TomTom Go Live 825 is experiencing some issues with charging - in that it won't. Every time it's plugged in, it just says "Charging paused - device too warm". It doesn't matter how cold it is (outside ambient temperature is about +5C), it always says that. It does it from the cigarette lighter socket as well as from a PC.

I've been advised that it might be a thermistor somewhere inside the device - does anyone know where it might be? Is it on the board or part of the battery?

Took it all apart and found what looks like an SMD thermistor (arrowed - first pic). But... this is a guess.



There are no markings on the silk screen next to this component other than S1 and S2 nearby, which can be seen from the pictures.

TomTom are being less than useless. The device is just out of warranty and are asking 105 Euros for a repair. What's making it worse is that they are refusing to refund the Live service subscription that my girlfriend very recently renewed and cannot use due to empty battery. For some reason, it won't work even if the device is running on external power (no choice here!).

TomTom devices seem so poorly made. Last year, her 820 blew up in a puff of smoke (literally). A zener along with a capacitor simply blew up. This is the reason she bought this new one, which lasted just over a year. I repaired the old one by replacing the blown parts (SMDs don't make it easy), which I was using until I got the 407.

Any ideas?

[dave406]

Sorry to hear that mate but i have heard about these doing this if left in sunlight or extreme heat during the summers. I just always uses Google navigate on my phone can she not do that or install the tomtom app?

[Captain Jack]

She spent a lot of money on TomTom to throw it away and use something else...

[jonsowman]

That could be a thermistor but it could well be just a resistor. Pretty sure it's not a capacitor.

Leave the device at 5C for a bit, then measure its resistance. Then warm it up to room temp and measure again. If it's changed by more than about 1% it's almost certainly a thermistor (rather than a resistor).

Thermistors are usually on the order of a few kOhms at room temperature.

[OllieNZ]

Is there a pcb attached to the battery itself? Assuming its a li-po battery.... If it is they're not overly expensive on ebay I bought a couple for an R/C chopper, did have to come from china though.

[mjb]

The datasheet for the Broadcom 59040 power management chip (which manages the charging of li-ion/lipo batteries) says it supports on-battery temperature monitoring - that's where you'll find your temperature sensor (which is almost certainly to be in silicon, speaking to the 59040 over i2c, not a discrete component)

A new battery should sort it. You don't want to be playing around with the safety stuff around lithium batteries as you can get some nice spectacular fires and explosive venting if they fail

[OllieNZ]

You don't want to be playing around with the safety stuff around lithium batteries as you can get some nice spectacular fires and explosive venting if they fail

Yup just look at the issues boeing have been having with the dreamliner

[Captain Jack]

Thanks guys! Was extra hoping that the temp sensor would indeed be on the battery itself. Will get this replaced as they are fairly cheap and see how it goes!

[mjb]

good luck, let us know if i was right or wrong