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mike-morris avatar image
mike-morris asked

Charger/Inverter Configuration for a boat

Hi all, i have a pretty general question although i feel it might illicit some complex answers. But here goes. We've just got a new boat and it has 6 x 12v lead acid batteries (110ah each), 1 starter, 1 for the inverter and 4 in a house bank for everything else. There was an old sterling 2000w inverter but that died. There is no shore power and no battery charger. So the batteries only get charged when out on the river - not ideal, particularly if she's left moored for long periods between visits.

I'd like to install shore power, fit a new inverter, a charger and an MPPT for solar input. So my question is what sort of config can you suggest. I'm feeling a bit stuck over what to do about the charger config when faced with 3 batteries banks. I thought about using a Multiplus 12v 3000 Inverter/charger but as far as i know this will only deal with charging a single bank.

Should i consider somehow making the 3 banks into one bank.

Just a bit stuck as to how to proceed.

Any help would very gratefully received.

Thanks

Mike

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2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

My preferred set up would be to shift the house bank to 24V, and to use a multiplus inverter. The starter batteries can be float charged, either with a small 240/12V, or a dc/dc converter. Charging the house batteries underway would require another dc/dc converter, or to replace the alternator with a 24V model.

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mike-morris avatar image mike-morris commented ·
Hi, thanks for your reply. I have 2 alternators through a splitter. I understand your thinking but i don't really want to have to replace the alternators. Out of interest, why is your preference to go to 24v? What are the benefits in your opinion?
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pwfarnell answered ·

If you use the Multiplus 12/3000 then I would go for a single domestic bank that feeds the inverter and the house loads using 5 of the batteries. Keep the starter separate and the Multiplus has a trickle charge connection to charge the starter. The only thing to be aware of is the trickle charge operates of the DC input to the Multiplus and is always active, but it does mean that solar power charging the domestic batteries also trickle charges the start battery.

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mike-morris avatar image mike-morris commented ·
Thanks for the reply. Yep - it would be my preference to do this, however i'm not sure if i understand what you are saying "trickle charge operates of the DC input to the multiplus and is always active".

Sorry - can you elaborate?

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pwfarnell avatar image pwfarnell mike-morris commented ·
The Multiplus has a trickle charge function. Some people think that this means when the Multiplus is connected to shorepower and it is working as a charger the starter battery trickle charge works. This is wrong.


The DC input to the Multiplus comes from the domestic battery bank, so typically at 12.0V to 12.8V when in use and 13.6V to 14.4V when being charged. There is a small power take off from the 12V DC in the Multiplus to the trickle charger which has a diode in which reduces the voltage by 0.5-0.6V and sends it to the starter battery. When nothing is being charged there is no trickle charge. When the domestic batteries are being charged the voltage is high enough to trickle some current into the starter battery. The diode prevents the starter battery from discharging into empty domestic batteries. This means the trickle charger also works when solar is charging the domestic batteries. My boat is set up like this, I also have the bow thruster battery connected to the starter battery by a voltage sensitive relay so all 3 batteries are kept charged.

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mike-morris avatar image mike-morris pwfarnell commented ·
Thank you so much for all the info - really appreciated. One question, is there a great deal of difference between the Multiplus and the Multiplus II
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kevgermany avatar image kevgermany ♦♦ mike-morris commented ·
Steel, not aluminium case on the II. Also lower standby current and other improvements. I'd get the II if you can. But the aluminium case is a good argument for the older model in a marine setup.
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