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I have a BMV-712 and a SmartSolar MPPT 150/70. Today as I was watching the readings on the VictronConnect app, I noticed that with no load, the BMV was reading about 15 watts less going into the battery than the MPPT said. For instance the MPPT would say the solar is producing 467 watts, but the BMV would show 452 watts going into the battery. At ~13.5 vdc, that’s about 1 amp of discrepancy.
Is this normal? Is the MPPT consuming that power? Is the current sensitivity set too high on the BMV?
How certain are you there was absolutely no load on the battery? Anything in standby etc.
There will always be discrepancies between the readings on different devices. The BMV voltage and current reading is more accurate than the MPPT.
15 watts difference from a reading of 450 watts is about ~3% variation, that is normal.
The important things to watch are:
Does the battery reach float stage almost every day.
Does the battery maintain a good stable voltage, even under larger loads and charges, without spikes.
If not, those can indicate a problem.
In response to your question: "Is this normal? Is the MPPT consuming that power?"
Yes the solar power displayed by the MPPT solarcharger is actually the PV power and not the output power, so you there will be a few % lost during the conversion.
With this small expected loss factored in, the MPPT power vs BMV power readings appear to be very accurate.
The BMV will obviously measure the power flowing into (or out of) the battery and is a proper measurement device, so as Guy stated will also be more accurate and should be considered as the 'master'.
In case you have any loads simultaneously active they also need to be considered and will effect the difference between the power readings.
