Dyson SV03/05 Battery BMS Thermistor

[NeilP]

Does anyone happen to know the value and type of thermistor NTC/PTC under the BMS of a Dyson SV03/05 style battery ?

I replaced cells in a pack and in pushing old cells out and then removing the PCB, discovered the thermistor is bonded in. By then the thermistor was broken.   Was not a worry as I have a few spare packs to play with.

Was wondering if anyone had ever unsoldered one and measured it or replaced one ?

Thanks

[tinfever]

In my firmware, I assumed it was a 10k thermistor with 3500k beta. The beta was mostly a guess since I don't think I actually tried to characterize it. If you look at the different beta values of thermistor, I think you'll find that in the range we care about, it only makes a few degrees difference, and since it is just for safety, even +/- 5 degrees is fine. I may have even reduced the overtemp threshold in the firmware to ensure the battery cell temp would never exceed the maximum, even with that beta uncertainty.

Temperature curve info:
https://github.com/tinfever/FU-Dyson-BMS/blob/main/firmware/thermistor.h

I think there are two curves because there are different resistor values used in the different BMS board versions.

[NeilP]

Thanks,
I’ll try and repair these boards and see how it goes

Was not able to measure originals,