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wiley1 avatar image
wiley1 asked

My BMV-700 never forgets

I have had my BMV for 3 years and I love it. Its tells me more than I need to know.

About a month ago, I disconnected my motorhome from shore power and turned off the AIMS inverter/charger. All would have been fine if I hadn't forgotten to flip off the Use/Store switch which left the smoke and CO detectors energized, drawing about 0.65 A. After about 652 hours (27 days), my four AGM batteries must have depleted to zero.

Yesterday, I reconnected the shorepower and today all is back to normal. The SoC is at 100% and voltage is 13.48. I was able to verify in the BMV history that the SoC actually did reach zero volts.


My question is how the BMV history was able to survive.

According to the specs, it needs a supply voltage of at least 6.5 volts to operate and it draws about 3 mA at 12 volts.

When the SoC fell below 50%, it should have gone into an alarm condition, closed the relay, and started using more than 15 ma.

How was it able to measure zero volts and record that condition in the history without a power supply?

Does it contain a non-volatile memory chip? Maybe a CMOS memory chip with a tiny battery?


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snoobler avatar image
snoobler answered ·


It didn't.


I think you're overthinking things.


My BMV-702 has never been attached to a battery that discharged to 0V. I suspect there was an instance where it sensed 0V for some reason, and since that's the lowest, it's retained it:


1649723694781.png


Nor has it ever been attached to a starter voltage (using the temp sensor) even though it indicates 46.21V.


I suspect it lost power as you would expect, and the 0V is the result of an anomalous reading - not a validation that the connected battery went to 0V.




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wiley1 avatar image wiley1 commented ·

You're suggesting that the settings in my device are just factory defaults? Come to think of it, the only one I actually changed when I set it up years ago was Capacity=200 Ah. But, after being without power, it was still set to 200 Ah. How is that possible?

Are you further suggesting that all the history I'm viewing is fake? Made up by Victron? Why would they do that?

Now I'm beginning to question whether or not my battery bank ever really did deplete all the way to zero.

Or, could there be a fat capacitor inside the BMV that holds the settings for a period after loss of power? Otherwise, why would we even have a setting for "number of full discharges". If the BMV forgets everything after a full discharge, what is the point of having that number displayed?

Below what voltage would you expect the BMV-700 to die and set itself back to factor defaults?





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kevgermany avatar image kevgermany ♦♦ wiley1 commented ·

Manual states history data is stored in non volatile memory. That must include settings as well.

Section 4.3, p33

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klim8skeptic avatar image klim8skeptic ♦ wiley1 commented ·
The only thing the BMV forgets should the battery go flat / disconnected is the SOC.

History and settings are stored in non volatile memory.

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