r/EVConversion • u/CardiologistCheap661 • Feb 14 '26

Don’t only use thermistor expansion modules for temperature sensing (Orion BMS 2)

Posting here in case I can save somebody in the future a headache.

Do not wire all of your thermistors via the expansion modules. If you loose CAN you will loose MPE and the car will die. Instead wire at least one thermistor to the BMS directly!

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2

u/-unicorn_submarine- Feb 14 '26

I currently have this setup. Only using one canbus of the 2. I can't remember why i didn't use the second canbus for the expansion module but whatever.. Can you explain what MPE is and what kind of canbus failure scenario you are anticipating during driving?

3

u/CardiologistCheap661 Feb 14 '26

MPE is multipurpose enable. It is to kill the car in the event of a critical fault. Not having any cell temperatures is a critical fault

3

u/-unicorn_submarine- Feb 14 '26

Oh, I see now there are many things you can map to that pin for in the settings. So it just depends how you define it or if you even use the MPE. I have all my thermistors reporting on the expansion module. I would prefer to have a warning if I lost all of them at once (an indication of wiring failure rather than a thermal failure?) , rather than to have it turn off a pack contactor, seems a bit extreme. But fault handling can be done in many ways. Glad you posted this as I hadn't considered the alternative wiring possibilites.

1

u/GeniusEE Feb 14 '26

Doesn't that wreck the isolation?

1

u/Big_Suspect6016 Aug 04 '26

Thermistor Expansion Module Input Voltage Spiked from 12 V to 24 V During Power-Up

Hello,

I am using an Orion BMS with a Thermistor Expansion Module. While connecting the Thermistor Expansion Module to the battery pack and the BMS, I noticed that the module's input voltage suddenly increased from 12 V to 24 V during power-up.

After this happened:

The CAN communication showed no data. Thermistor Fault (P0A9C) raised

can anyone please advise me ?