Split Charging from MPPT through Battery Protect

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stevecounsell asked Jun 15, '20

Split Charging from MPPT through Battery Protect

I have an Autotrail Motorhome with a Sargent Electrical unit that used to provide split charging for my Leisure and Starter batteries.

Last year I had installed the following system:

200amh LifePo4 Victron battery

Multiplus 3kva inverter charger

Victron BMS

Victron BMV712

Victron 200watt Solar Panel AND a SmartSolar 75/15 MPPT Charge Controller

Victron SmartSolar 75/10 MPPT for the original 100watt solar panel (removed the PWM charge controller and bypassed the Sargent Unit)

Battery Protect on the "output" side of the battery / system

Battery Protect between a Sterling Power DC-DC battery charger and Lithium battery

(Sterling charger runs of the starter battery / Alternator while the engine is running)

MY QUESTION IS:

Can I introduce a "Split Charger" between the once of my MPPT Charge Controllers and my starter battery using the cables already in place (or new cables)?

Which Victron unit would I need? (Cyrix...?)

Thanks in advance

Steve

battery charging Cyrix Battery Combiner

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Answer 1 · 2020-06-17T08:58:00Z

dazey77 answered · Jun 17, 2020 at 08:58 AM

I think I see what your trying to and I think there are some fundamental issues with it.

Am I right in thinking that you have a split charge route from cab-coach in the form of the sterling and you want to introduce a second route coach-cab to charge starter battery?

If so, couple of problems.

1-The battery protect is one way, so you can't use this cabling as a route

2-I am not sure a simple Cyrix would work as you have different battery chemistries and it would be nearly always closed when the engine was off.

3- your also creating a loop where there is the potential for the sterling to be charging the lithium thats charging the sterling when the engine is running. Depends on the sterling setups but as the lithium charge voltages are higher its possible that this could occur in absorption phase (could be 14.6v) and if the Cyrix was closed it would stay closed.

Would be better just dumping a small solar panel on the dash to keep the cab topped up if thats the issue.

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stevecounsell commented · Jun 17, 2020 at 02:08 PM

Since I asked the question, I'd been thinking the same sort of thing. A small additional solar panel connected to the started battery.

You hit the nail on the head with your answer and understanding my issue. Thanks for that :)

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