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Michael Williams avatar image
Michael Williams asked

Lower than expected current reading with BMV-712 battery monitor?

I've been ignoring this 'issue' for a little while, but now have time to see if I can figure it out. My bmv-712 monitor seems to read current on the low end or approximately under half of what I expect it to display. One example is my maxxair fan should be drawing ~-0.9A at a specific speed, however the monitor displays -0.36A. The same goes for the other accessories I have and I'm aware that listed startup current is typically higher than constant draw. I can't take a photo at the moment, but I'm fairly confident I have things set up correctly. There are no loads between the battery negative and the shunt and it's positioned in the correct orientation.

Any thoughts on what's happening? I'll provide a photo when I can.

Thanks!

BMV Battery Monitor
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2 Answers
Mark avatar image
Mark answered ·

That sounds a bit odd...

I would firstly double check that A) your using the correct supplied shunt (50mV / 500A) and that the BMV settings match this in Victron Connect (Look in settings > Misc).

Then check all connections and maybe disconnect everything and do a 'zero current calibration' (Under settings > Battery).

Also, how do you know what current it 'should' be drawing - are you using some other measuring equipment or referring to a label that could indicate max current?

If your still having issues then its best to speak to your dealer for further advice.

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Michael Williams avatar image
Michael Williams answered ·

Mark, going through your list and just to double check myself:

1) BMV settings in the app and shunt are both correct.

2) I've done the zero current calibration with everything turned off (not disconnected). I'll try physically disconnecting everything later today to see it that makes a difference.

3) I don't have the clamps for my multimeter with me right now, but going off a) the difference with positive current coming from my charge controller and battery monitor reading with zero load and b) the expected current draw based on secondary source readings for specific accessories, such as the maxxair fan, the difference in current is greater than what I can chalk up to differences in measurement.

Attached below are two screenshots of the current reading from the battery monitor and charge controller.


smartselect-20190802-105719.jpg (64.6 KiB)
smartselect-20190802-105731.jpg (73.9 KiB)
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Mark avatar image Mark ♦♦ commented ·

Yes assuming that there was no change in conditions between the time when the 2 screen images were taken I can see that there is a delta of 5.4A (9.1A - 3.7A).

If you believe that the active loads are not capable of drawing the 'missing' 5.4A, the best next step would be to temporarily totally disconnect ALL loads during the next charge cycle and see if the readings then match more closely.

There will always be some variation as the MPPT is not considered to be a measurement device, but if everything else is totally disconnected then the 2 readings should be fairly close.

In general the BMV should be considered as the master as it uses a calibrated shunt to measure current.

If there still seems to be an unreasonable difference after a proper test (where all assumptions are excluded) then your best to refer to your dealer for further support.

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