question

sportswagoneer avatar image
sportswagoneer asked

Can a multiplus be used as a power supply without a battery for winter storage?

I’m looking to upgrade the old Sterling charger and china inverter in my sailboat to a Multiplus 12/1600/70. But I’m unsure about winter storage (on the hard in Norway - frequently with freezing temps.):


I have a drop-in LFP battery bank which should not be charged when freezing. BUT to keep track of the boat I also want to keep the Cerbo GX, a router and a webcam running. These are all powered by the boats 12v system and monitors that same system (BMV 712 is also left running.) To accomplish this, I have simply disconnected the negative end of the smartshunt from the boat system, leaving the batteries inert while the AC shore power connected Sterling charger powers the Cerbo etc.

Can I do this with the Multiplus (in charge only mode?) or will it fail without a battery?
If not: Any suggestions for a work-around?

Multiplus-IIcerbo gx
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3 Answers
Alexandra avatar image
Alexandra answered ·

@Sportswagoneer

A bypass switch is the way.

No it is not good to have the inverter in charger mode without a battery.

The inverter can and should be programmed with a lifepo4 profile to not charge below a temperature, the default is 5°C you can raise that if you want to. If you have a temp sensor connected to the battery bank (either direct to the inverter or using the shunt if you have a GX). It won't do so so the batteries will be safe in that regards.

The cerbo has extra options to add more monitoring for temperature as well.

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sportswagoneer avatar image sportswagoneer commented ·

Thanks for your reply! I’m aware of the temperature limitation setting and have a sensor on the batteries - but in the winter, there’ll be months of continuous freezing temps. So if I power the Cerbo etc. from the battery and the Multiplus doesn’t charge - then i’m afraid the battery will just empty which is even worse.

What kind of bypass switch are you thinking of?

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Alexandra avatar image Alexandra ♦ sportswagoneer commented ·

In your case it is probably best for a total system shutdown. Unless you want to pay for the other option that is battery warming.

You could get an ip65 and run that as a 12v power supply from shore to keep the cerbo going. But it sounds like in your case there is no need if the reat of the system is off.

If things need to be powered in the boat then an AC bypass.

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mvas avatar image
mvas answered ·

No. The Multiplus is a Battery Charger and a DC-to-AC Converter. Where did you read that it is a DC Power Supply? If you disconnect the battery then you need a 12 Volt Power Supply to operate your 12 volt equipment. Or you can keep the Lithium Battery above freezing.

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sportswagoneer avatar image sportswagoneer commented ·
It’s simply a matter of what my old charger COULD do and what a Multiplus can do. I have arrived at the same conclusion - it can’t. So I’ll either keep the old one as a winter PS or get a simple 12V PS for winter use.
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sportswagoneer avatar image
sportswagoneer answered ·

So I’ve been pondering this. During winter there’ll be extended periods of freezing, so the 5° cut-off simply won’t allow for enough charging.
BUT: I have a regular sealed lead-acid starting battery which would benefit from being kept charged over the winter. So my current plan is to disconnect the LiFePo bank at the negative end of the shunt as usual and then run a provisional 6m 16mm2 cable from where the Multiplus connects to the positive pole to the positive pole of the starter battery.
I’ll have to reconfigure the Multiplus over the winter to a new battery chemistry and limit the DC amps output to 10 amps. Starter negative will run to the bus bar as usual. The lead battery will simply remain topped-up and the charger will power the (minor) DC loads but have a battery to work with. The BMV and Cerbo however will not measure the “active battery” - but as long as I don’t activate DVCC, the Multiplus should be fine, keeping track of the charging voltage directly on the DC terminals….?
Any thoughts on this approach would be appreciated.

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