I am refitting my sailboat and have 2 separate battery banks. I’m trying to figure out the best way to connect charge and load to the battery banks. I have charging coming from the engine alternator and solar panels (via an MPPT charger). I am considering two options, both using a DC-DC charger between the banks. The question really is whether it makes more sense to connect the solar to the “house batteries” or the “starter battery”. See OptionA & B diagram below.
I would appreciate any input or general critique of this design, thank you for the help!
If the battery banks are of similar or identical voltage ranges, then you could use a Cyrix charge relay between them, rather than a dc/dc converter. With your layout, the dc/dc converter would need to be disabled before the “both” position is selected on the switch.
Also, you may need to be able to independently isolate both batteries from all loads, and also the starter should not be controlled by the same switch as the house loads panel.
Thank you Mike, I understand what you are saying. Right now both banks are 12V AGM.
If I select the “Both” position that will connect the two inputs of the DC-DC charger, so I guess that is not suggested without disabling it first.
What is the suggestion system design for this situation? I would imagine that having two battery banks with selector switch and alternator and solar charging is fairly common.
mmm.
Have a look at Victron’s wiring Unlimited book. Wiring Unlimited - Victron Energy
The isolator switches should isolate each battery totally. This could be achieved by wiring the alternator to the same C terminal as the starter, and the solar charger to the house switch. The Cyrix could be an exception to this - as could a bilge pump. I think that the cyrix will also give you an emergency parallel function, so that may also be useful.
I am trying to avoid wiring the Solar Charge Controller to the C terminal, because that is the configuration I had previously and the Solar Charge Controller has a voltage sensor connected to Bank2, so if you use the selector switch to connect it to Bank1 it will charge incorrectly because it is not getting accurate voltage feedback.
Then fit a separate isolator for the charge controller. Remember, if the device fails, the switching FET’s tend to go short, leading to large currents in the supply wires. This should have both a fuse and an isolator switch (can be combined in one unit) so as to enable easy cut off in an emergency.
