jwfrary avatar image
jwfrary asked

Paralleled Multiplus with AC and DC generators

Ok, so. We are on a boat.

we have 2 paralleled multi plus 24/3000/70/50 with a 560ah battery bank comprised of 4 agm exide ep1200.

AC power is provided either by the 7kva gen or shore power. The multis are set to 12.5 and so 25amp overall. There is a victron battery monitor connected to the colour control gx and the system uses that for SOC. Additionally there is also some DC charge from the alternators on the boat but it’s likely small enough in the real world the be discounted. My question is. Should we fit a DC generator to supplement the AC system and the battery’s were in a discharged state. The DC generator might deliver already in excess of what is required to the batteries, plus if the AC generator is running the Multiplus might deliver a charging current, how can I be sure that in all scenarios and without intervention that the batteries cannot be overcharged. I know that in all likely hood the Multiplus could be set to stop and start the DC generator as demand changes. The system supplies and acts as UPS for a survey suite so the priority to maintain power and have a back up to. I look forward to your responses.

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2 Answers
kai avatar image
kai answered ·

Any reason why you would want to introduce a DC generator when you already have an AC generator. The technology type introduces another interface you need to deal with; what about upsizing the AC or another AC gen?

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jwfrary avatar image
jwfrary answered ·

Kia, yeah good question. Partly we have other dc banks onboard that could be charged by the dc gen. another advantage would be the ability to ru. Both generator to support higher loads using the power assist function of the Multiplus without the batteries discharging.

Redundancy in two units. And the abiiity to better match generator and load as we have quite a varied load requirement between time of year and type of equipment we have onboard.

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kai avatar image kai ♦ commented ·

ok, if you've done the cost/benefit analysis, I don't think there's any technical reason why you can't make it work.

Think of the DC generator as another source, in some ways not unlike a solar panel array through a MPPT.

The DC generator will need to have some smarts to understand when to back off or cut out the charging current. In fact I think there's a couple of threads here about feeding a stiff supply (like a DC gen) into a MPPT, instead of solar, to charge a battery bank. You'll have to work through the associated risks...

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