@muem, what device are you using to measure 31mA current draw, and where are you taking the measurement, and with what other devices connected to the battery bank?
...if you're measuring with anything other than a Fluke, I wouldn't be too concerned about it; consumer-grade DMMs are frequently irregular/inaccurate below a quarter of an amp.
@muem, hmmmm so there's a couple things here:
1. If you're measuring 12.56v at the battery and only 11.92v at the controller, then you've got a massive amount of voltage loss between the battery and the controller (very possibly caused by undersized cables and/or loose connections/poor crimps/etc.) that you'll need to address before you can ascertain accurate self-consumption readings.
2. Without having the battery uninstalled from the system, you won't be able to ascertain accurate readings because there are -in any automotive installation- numerous sources of constant but minuscule system loads. Just having the ignition switched off isn't enough, because there is always going to be a tiny draw going to your system computer to maintain time and system memory, your stereo to maintain time and memory, not to mention tiny loads such as LED status lights, underhood lights, etc. If you're truly concerned about measuring 31mA vs 20mA, you'll need to disconnect your battery from the system entirely, then check your wire sizing and all of your connections to figure out why you're getting a massive voltage drop between the battery and the MPPT, and then after that problem has been corrected, re-measure the self-consumption of the MPPT while you have literally nothing else connected to the battery.
Oh – it’s a mistake. It’s not the voltage drop across the line to the battery. It’s the voltage drop at the built-in shunt of DMM. Only during the measurement 11,92V are applied at the MPPT. Without DMM the voltage is 12,56V.
