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kyleolmstead avatar image
kyleolmstead asked

MPPT 75/15 Multiple Battery Types

I am installing a Smart Solar MPPT 75/15 on my boat, and will wire it to an AGM battery (Deka 8A4D). My engine starting battery (lead acid Deka 904D). The AGM will power the house loads and the starter battery starts the engine - they have separate positive cable runs. However, when my engine is on or when I am connected to shore power, I combine the positive cable runs so both batteries will charge from the engine or shore. This also means that the Smart Solar charger will now be charging both batteries. Are there settings on the MPPT that will work for this scenario? What are the drawbacks? Or should I not do this at all? (I suppose one work around would be turning off the charge controller when the engine is on, but that's not ideal.)

MPPT ControllersAGM Batterylead-acid
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spirou avatar image spirou commented ·

Realistically, the 75/15 won't put out so much charge to make a difference for the starter battery in those cases when you're on shore power or running the engine. It will just go to float when the alternator or charger gets the batteries up to whatever voltage as those will be supplying the bulk of the charge.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The default charging algorithm suits for the most lead batteries (AGM is also a lead battery), so you should be fine doing so.

But instead of using manual switch I would recommend you to use a cyrix-ct.

https://www.victronenergy.com/battery-isolators-and-combiners/cyrix-battery-combiners

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