Best way to charge starter battery in camper van?

I’m about to move my 12V system from a class A motorhome to a class B camper van and need to sort out starter battery charging. I have a Multiplus-II 2x120V, Cerbo GX, SmartShunt, 150/100 solar charge controller, etc. I will be adding an Orion XS for alternator charging. I’m pondering ways to trickle charge the starter battery when parked for a few days, since it is used for running chassis electronics and lights, power door, etc.

What I would like to do: Monitor the starter battery voltage and automatically start charging only when the voltage drops below a defined value. Charging when there is incoming solar or on a schedule would also work. If that’s not feasible, something that I could start and stop via the app and/or a physical switch is also an option.

What I’ve come up with so far:

  • Add a second Orion: This seems like overkill and I haven’t yet figured out how to make it work automatically based on something like starter battery voltage, solar, scheduling, etc.

  • Use the trickle charge circuit from the Multiplus and manually control it with a relay through VRM, etc. Same as above in that I haven’t figured out a way to automate it yet.

Does anybody have any better ideas on how to make this happen? Thanks in advance for your help.

A couple of thoughts. I have not used either but consider them viable options having considered this myself.

  1. Pass it through the Cerbo GX relay and then control it via Node Red. This could monitor both starter and house battery voltage to decide when to charge. The code has to be quite clever if working off the starter battery voltage to check for low voltage, charge for a defined period then stop and wait for surface charge to dissipate before checking voltage again.
  2. Pass it through the relay on the MPPT and have the relay function set to day detection so you know you have solar.

Thanks. Great ideas.

I haven’t played with Node Red at all, but I would like to eventually. I’ll leave that as a project for when I get some free time, as I definitely want an excuse to learn how to use it.

The MPPT relay seems like a good option in the interim. Couple questions:

It looks like the relay can handle 4A, which is also the output of the Multiplus trickle charger. Do you think it would work to pass that through the relay directly or do I need to have the relay trigger an external relay to be safe?

Since the trickle charger has such a low current, would you expect it to cause any issues with the Orion, such as the engine shutdown detection? I can run an ignition trigger wire for the Orion instead if I have to, but would prefer to avoid it (the other wiring for the Orion has already been run).

The relay is on the limit, Victron do not publish data on how the current varies with voltage difference between the batteries. To date many people have discussed using the relays but there are few reports of success. One is linked below. You could search the old community archive.

https://communityarchive.victronenergy.com/questions/79720/multiplus-aux-trickle-charge-function.html

The trickle charge can interfere with the Orion. There was a case a few months back showing this were an ignition wire link was added.

Looks like I’ll have to play around with it a bit. This gives me a good starting point. Thanks again for your help.