captain-p avatar image
captain-p asked

Combining Victron MPPT and Argofet

I have a small boat with 1 battery (starter), a Suzuki 30HP outboard engine (which can also charge the battery), a Victron MPPT 75/10 charge controller. This unit has a solar panel (30W) connected to it.

A simple setup that works well:


However, I want to install a second battery (service battery) for stuff like radio, lights, water pump and more gadgets. For this to work efficiently, and have both batteries charged, I think I need an Argofet battery isolator.

But the MPPT manual does not say how to connect that, and the Argofet manual does not show how to connect things if you have solar power with the MPPT AND an engine that delivers a charging current; it just shows 1 alternator as power source.

Can anybody help me out?

MPPT SmartSolarArgo FET Diode
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1 Answer
Justin Cook avatar image
Justin Cook answered ·

The MPPT manual won't have instructions for this because it's not a supported solution; the MPPT is not able to accurately charge two separated batteries that will each have their own voltages, capacities, and etc - it is designed to charge a single battery bank.

The ideal way to accomplish your end goal is to either: 1. add a second panel and controller to charge the second battery; 2. only charge one battery while using a DC-DC charger from that battery to the other; 3. install a battery combiner/isolator relay like the Cyrix-ct; or 4. just parallel the two batteries so they're now one battery bank with a single voltage reference that the MPPT can see and charge appropriately.

It is possible to do what you're suggesting by just running the MPPT battery output +ve to the ArgoFET +ve input post -I tested this many years ago- but since the MPPT will no longer have any consistent vBatt reference to tell it anything about the battery it's trying to charge, it's not really the greatest idea ever and may lead to odd behaviors in the MPPT charging stages and/or inconsistent and less than ideal charging being delivered to both batteries. Will it probably more or less work? Sure, but undertake at your own risk.

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captain-p avatar image captain-p commented ·

Thanks for the suggestions. Using an Argo Fet was just a thought - if i'm better off with another product that's fine too. I will look into the Cyrix-CT solution.

I think I could also just install the new service battery, connect MPPT and all load to that one and leave the starter battery to the engine, completely separate.

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