Max Flentge avatar image
Max Flentge asked

Smartsolar to starter battery and orion tr to auxilary battery


I'm thinking of upgrading the electrics in our Campervan.

Currently the alternator and solar panel charge both batteries simultaneous. I would like to disconnect the starter from the auxiliary battery to prevent draining the starter battery by accident while camping.

My thought is to hook up the Smartsolar controller to the starterbattery to keep it charged while not using it and hook up an Orion TR between the starter battery and the auxiliary battery.

When the engine is not running, ideally the Smartsolar would charger te starterbattery first, and the Orion TR will use any excess power charging the auxiliary battery.

And ofcourse the Orion TR will charge the auxiliary when the engine is running.

My questions are:

- Is this a good idea?

- Won't the Orion TR drain the starter battery because it consumes more power than the Smartsolar produces?

Looking to hear from you, much appreciated :).

Best regards,


orion-tr smartsolarsmart solar set-up helpcampervan
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3 Answers
Sarah avatar image
Sarah answered ·

Hi @Max Flentge - first question is do you have lithium batteries? I am assuming you don’t.

Without knowing the exact specifics it is hard to tell the best option as every install is different. You might find a Cyrix battery combiner connected betwee the starter and house battery meets your requirements. In this instance I would suggest hooking the solar panels to the house batteries. When the alternator is running it will charge both batteries, when the house batteries are charged any excess solar energy will top up the starter battery. This of course assumes that your starter battery is only used for the engine/vehicle and not really at a risk of going flat.

If you had lithium in the mix I would definitely recommend the Orion DC-DC charger. Have a play with the Orion (VictronConect demo library) to investigate charge enable/disable voltages if you are still interest in going down this pathway.

I hope this help as an alternative. What you we’re suggesting is not necessarily wrong just maybe not the best solution - again it all depends on what the overall config looks like and your objectives.


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Max Flentge avatar image
Max Flentge answered ·

Hi @Sarah,

Thank you for replying. I indeed do not have a Lithium battery, rather to AGM batteries.

I have considered the Cyrix Battery combiner, but read that this be be less optimal in terms of fully charging the auxiliary battery (as the alternator is not a charger) and will that them for about 80%.

The reason I am curious to find out about the mppt on starter battery setup is that I think it could combine the best of both worlds:

- No flat battery after having the camper stalled for winter

- Full auxiliary battery because it's properly charged by the dc/dc charger

- Excess solar power will be send to the auxiliary battery through the dc/dc charger

So the main question still stands I guess: MPPT > Starter > Orion > Auxiliary, will it work? :)

I'm a bit scared when the solar panel creates a high enough voltage, the DC/DC will kick in (as expected) but will draw too much current draining the starter battery.

Best regards,


1 comment
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Sarah avatar image Sarah commented ·
@Max Flentge what you are suggesting makes sense (and will work without discharging the starter battery provided the charge disable voltage is set high enough) and you are correct there are limitations of using an alternator to charge a large auxiliary AGM bank. You do however risk the Orion becoming a bottle neck (alternator + MPPTs) to charge the auxiliary batteries. It will also mess with the mppt charging algorithm which may not be healthy for the starter battery.

From a design perspective you are trying to do three different things. Maximise alternator charge to the auxiliary batteries, use solar to charge the auxiliary batteries, and trickle charge the starter battery. Try to keep the design as simple as possible (alternator-Orion-auxiliary and mppt-auxiliary) and investigate options for a small fit for purpose 12v trickle charger for winter use.

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kevgermany avatar image
kevgermany answered ·

You shouldn't have loads on the starter battery when you're camping. The worry is that the van is wired so that the starter battery and auxiliary battery share your camping loads. Check/change. Check the aux battery is large enough.

Then as above MPPT to aux battery.

Orion from starter/alternator to aux.

Votronic make a trickle charger which will keep your starter battery topped up from the auxiliary system. A second Orion for this is overkill.

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