# Can I charge a multiplus 12/3000/120 with an identical charger on another boat?

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Kevin Windrem answered ·

I don't think interconnecting the two boat's DC systems is a good idea due to the long, large cables needed. You could take AC out of one boat and use it as "shore power" on the second boat.

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@DuncanDavis

Trying to understand here.

You want to use a multiplis ac out to another multiplus ac input to boost the battery on the second unit in the chain? Is this using the shore power through the first unit to the second?

@Kevin Windrem mentioned this ac to ac connection.

Yes you can if the charge limit (or input current limit) is down on the second unit so as to not overload the first unit or the input of the one on the shore limit.

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Thanks. The answer seems to be yes I can charge the batteries on a second boat from the AC output of the first if the input current limit is down on the second unit. I know this is not an efficient way to do it but occasionally it is the most convenient. I do not have an on grid supply. Normally the solar will suffice but sometimes I need to top up.

duncandavis

Considering that DC-DC converters are commonly around 85% efficient and a multiplus at 1/3 load is around 90-94% efficient it would be interesting to see the difference. The Victron IP65 chargers are rated fast 90-95% efficient but I can’t find the charge efficiency of a multiplus.

If there is any considerable distance between the systems it might be more efficient due to voltage drop in long cables.

I would love to see a comparison as I feel that the efficiency difference would be surprising.

Edit. I decided to test this albeit not exactly scientifically.

Using a multiplus compact 24/1600 feeding into a multiplus 24/3000 with seperate battery banks and with the larger unit set to 5A maximum input, I recorded efficiency as 69-73% according to readings from the BMV’s.

( 830W in from 1200W out with minor DC loads (less than 50W) running on the second system )