Is it a thermocouple, resistance (PT-100, PT-1000, other) or some other kind of sensor?
asked
BMV-702 temperature sensor type
I can confirm that it is not an LM335Z, and I'm pretty sure it is not a PT100 or PT1000, as those are RTDs (Resistance Temperature Detectors). I am fairly certain that it is a NTC Bead Thermistor (we had a damaged one that we opened up to look at). My calculations indicate a 150kΩ (@25°C) with a B parameter of approximately 4021K. The only issue is that I can't seem to find one from suppliers like Mouser or Digikey.
It is definitely an NTC Bead Thermistor. We found one that is close. Vishay PN NTCLE100E3154GB0. B-parameter of 4370K. It is remarkably close to the Victron original.
@dtaschler, what makes you say it's an NTC thermistor? I recently bought a BMV-712/BMV-702 sensor (ASS000100000), and attempted to measure its open-circuit parameters: it has > 10MOhm resistance, and is also open in both directions when tested as a diode (to 17V).
I'm guessing it's a LM35 or similar IC configured in a two-wire circuit (e.g. figs 17, 19 of the LM35 datasheet).
@dtaschler so could you explain (if you recall) how you wired up the NTC thermistor to replicate the ASS000100000? Did it work? You never answered @BenL‘s questions.
It's a bit of a mystery at the moment.
I'm pretty sure it's not a thermocouple.
I'm pretty sure it's not a data type one like DS18B20
I think it's most likely a zener based one like LM335Z (but it is not LM335Z).
Resistive is quite possible too.
So if we share one temperature sensor output between two BMV-702, shall additional error be small, like less than 1 deg C?
Hi Aare; you’ll have to test that to find out. I’m sorry but its not a use case common enough thath I want one of our r&d engineers to spend time on making an answer.
dtaschler said: It is definitely an NTC Bead Thermistor. We found one that is close. Vishay PN NTCLE100E3154GB0. B-parameter of 4370K. It is remarkably close to the Victron original.
I have just verified this. I swapped out an actual BMV702 temp sensor...with this NTC thermistor...and was identical temperature.
@Craig Myatt so you verified that the ASS000100000 sensor uses an NTC 150k as @dtaschler described.
Besides the NTC thermistor itself are any other parts required? Just hook up 12v to one lead, and send both leads back to the SmartShunt or Dongle?
(Some have claimed it’s is not a NTC thermistor but an LM35, any comments?)
