Common ground between 2 battery banks of different voltage for BMV 712

DIY
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1

Good morning, in your off grid cottage we have a Generator using a 12V starter battery and a 24V solar/inverter system including a Multiplus, MPPT, BMV 712 and a cerbo GX.

The generator and the solar system are about 150ft apart and I would like to be able to monitor the starter battery trough the 2nd input on the BMV-712 so it can be displayed on the cerbo GX ( display only I don’t need to have any charging of the starter battery from the solar system).

The documentation call for the negative of both battery bank to be bound together but at no places I found any information on the wire size to use for that bound can it be just a small awg 12 or 14 ?

Thanks

2

Normally in boats or vehicles the common ground is large as it also carries starter motor or alternator charging currents so it is always suitable.

In your case it will only need to carry the sensor wire current, a few mA so it can be small, as you say 12 or 14awg, and these will avoid voltage drop over 150ft. However, I would suggest that you put a 1A fuse in the negative wire as well as the positive wire.