Michael Connolly avatar image
Michael Connolly asked

24v LA starter batteries and 12v Lithium House charging

Hi all

Motorhome setup includes 400ah house Lithium setup, three Mppt 100/30 with 1.6kw solar and a genset . The truck starter is a 24v (two 12v) lead acid batteries which is charged via alternator.

I would like to top up charge my Hpuse batteries while driving from A to B but do not want to connect the alternator to the Lithium batteries (via charger). Instead I want to use the 24v starter batteries as a source for charging the Lithiums.

I believe that what I need is...

Solenoid connected to ignition to ensure charging only when ignition is on (alternator running)

VSR to protect the starter batteries from being drained too much

A MPPT 100/30 to feed the 24v starter battery power(via the solenoid and the BSR) to the Lithium house batteries using the same lithium charge profile I use from the solar panels.

Is this a workable solution AND what Victron products will do this for me.



victron products
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1 Answer
JohnC avatar image
JohnC answered ·

There's probably a few ways you could approach this Mick. Possibly the simplest is just to accept a 'Float' V from your 24V system with a Victron Orion. Ie. not a full charge profile.

There's a helluva range of em, and what you choose may depend on what your alternator can do, so it doesn't drain the 24V batts even when the engine is running.

Maybe one'o'these:,-non-isolated-EN.pdf which also mentions an engine switch.

The A ratings refer to the 12V side.

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Michael Connolly avatar image Michael Connolly commented ·

Thanks for your reply. I have an item like this already, it’s a Redarc CE40-13.8 which is a similar item. I wanted to use a lithium profile and I happen to have a spare MPPT 100/30 that I can use for that. Do you have an idea for a VSR for the job?

Again thanks


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JohnC avatar image JohnC ♦ Michael Connolly commented ·

I can't help with the VSR. To me starter batts are sacrosanct, not to be used for anything else (mariners stuck on the high seas, etc.). Excess via alternator open slather, but engine prompted.

Your Redarc might do. I share your concern for Li's, but most bms's should accept a set float V.

That said, your spare 100/30 should accept a 24V supply and charge as you wish, switched in as you wish.

I note your concern with alternator vs batt supply. Works out the same, just wire length isn't it?

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