question

sek avatar image
sek asked

Can I use MPPT output to charge/float battery?

Hi there,

I have a MPPT 75/15 in a boat charging a dedicated house battery and I would like to know if I can connect the output to keep the other 2 cranking batteries charged while boat is stored.

Thanks

MPPT SmartSolar
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1 Answer
kevgermany avatar image
kevgermany answered ·

If the batteries are all the same chemistry/voltage and your wiring is OK, yes. You might find the boat is already wired for this with a switch that connects start and house for boost when starter batteries are low.

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sek avatar image sek commented ·
Hi Kev,

Thanks for replying.

All batteries are light-deep cycles lead acid.

I have done the wiring for the solar and house batteries, I've got a two-way switch which is there only to isolate as I've added a combiner to allow charging of both batteries once the load is available.

there's an Anderson on the end of the load cable that I can connect to the batteries but I'm not sure what voltage to go for as usually they will be nearly full battery just needing topping up and floating....

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klim8skeptic avatar image klim8skeptic ♦ sek commented ·
@Sek There is a risk that when starting the engines, high current can flow from the house batteries to the start batteries.

A risk of blowing fuses in the mppt/wiring that is only rated to 20a.


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sek avatar image sek klim8skeptic ♦ commented ·

The charger would only be connected to cranking batteries while the boat is parked.

I'm unsure if I have to set the load output of the charger to a certain voltage similar to the floating phase.

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kevgermany avatar image kevgermany ♦♦ sek commented ·
MPPT will start a charge cycle daily. This will switch to float automatically. If the boat will be left unused for long periods, it might be a good idea to set a short max absorption period in the MPPT.
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sek avatar image sek kevgermany ♦♦ commented ·

I usually use the boat every couple of weeks on average.

To be clear, when you say to set the short max absorption period is that for the house battery connected to the "battery" outlut or the two cranking batteries that I want to connect to the "load" output?

Thanks

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