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aare avatar image
aare asked

BMV-702 temperature sensor type

Is it a thermocouple, resistance (PT-100, PT-1000, other) or some other kind of sensor?

BMV Battery MonitorTemperature Sensor
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dtaschler avatar image dtaschler commented ·

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.

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dtaschler avatar image dtaschler commented ·

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.

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benl avatar image benl dtaschler commented ·

@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).

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2 Answers
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wkirby answered ·

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.

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aare avatar image
aare answered ·

So if we share one temperature sensor output between two BMV-702, shall additional error be small, like less than 1 deg C?

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

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.

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dtaschler avatar image dtaschler commented ·

Being that the temp sensor uses resistance, it is possible that there will be significant error when two BMV devices are in parallel.. As stated earlier, test to confirm.

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