Victron 12|12 30 and reverse current?

DIY
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1

I have a Victron 12|12 30 DC/DC charger on my sailboat which I use to keep my house bank (2 x 12v AGM) batteries from discharging when not connected to shore power. I feed the house bank with a large Lithium battery bank which is independent from the AGM bank and put the Victron in constant output mode at 12.5v which seems to work well and keeps the AGM bank from discharging when running appliances (refrigerators, nav equipment, etc).

My concern is, however, when running the engine the alternator which charges the AGM bank puts out around 14V so the normal output of the Victron (12.5v) will be lower than the voltage being fed into the AGM bank by the alternator. Is there any kind of reverse voltage protection built into the Victron? I don’t want current from the alternator coming through the Victron to the Lithium bank. The Lithium bank is charged with solar power and the 12v output that goes to the Victron input is not designed to charge (reverse current). Will the Victron prevent this scenario?

I know this is a very non-standard way to connect these two battery systems but the Lithium system is an independent battery/inverter/solar charger which is not permanently attached to the boats AGM bank.

I’m afraid if I have the two banks connected through the Victron 12|12 30 that the current will flow in reverse direction when the ships motor (alternator) is running.

2

To update. I did some testing and it does seem that the Victron does allow some reverse voltage into the output of my lithium bank when the voltage of the lithium bank is lower than the AGM bank. With the DC output of the lithium bank turned off I measured 1.5v coming out of the Victron’s input. I’m not sure this would cause a problem but I think I’m going to install a anti-diode inline just to be sure. I would rather not if I could get away with it because a diode will drop the output voltage from the lithium bank by 0.7v but it will block any reverse current which is the thing I’m concerned about.

3

I suppose a current measurement instead of a voltage measurement would be more useful to determine if any reverse current flow is occurring when the lithium bank is at a lower voltage.

4

Yes, because any minor leakage current at the level of micro amps can raise an open circuit voltage