Charging the engine start battery...

[MoominPapa]

I current have one of these: clicky which, despite having outputs for three battery banks, is connected only to my domestic bank. The boat is not live-aboard, and over the winter it's likely that the engine will be run only rarely. More often, there will be people aboard (we have lots of "jobs" to do!) and so there will be shore power connected maybe one day a week; our marina discourages leaving shore power connected to unoccupied boats. I'd like to make some arrangement to keep the engine battery topped up over the winter time and I'm wondering about the best way to do it.

 

I've poked around inside the charger, and as far as I can see, there's just a diode-based split-charge circuit connecting the three output to a common switch-mode charger. It's not obvious how battery voltage is monitored, but given the intructions insist on using the "battery 1" output first, my guess is that one is monitored and the others just take their chance.

 

I'm concerned that just using the "battery 2" output will overcharge the start battery. The domestic bank is 660Ah, versus 150Ah for the start battery, and when the charger is running the domestic bank is likely to be much more discharged. If the charger regulates to bring a discharged domestic bank up to 14.4v, that's likely to push too many amps through the start battery.

 

This version: clicky would seem to be the ideal solution, it has a trickle-charge output for the start battery, but that's not what I have.

 

I can see these choices:

 

1) Don't bother.

2) Just connect the start battery as "battery 2"

3) Connect the start battery to battery 2, but with a power resistor in series to reduce the charge current.

4) Use some other method to get a trickle charge.

 

Please could the battery gurus advise?

 

 

MP.

[Gibbo]

I'm concerned that just using the "battery 2" output will overcharge the start battery. The domestic bank is 660Ah, versus 150Ah for the start battery, and when the charger is running the domestic bank is likely to be much more discharged. If the charger regulates to bring a discharged domestic bank up to 14.4v, that's likely to push too many amps through the start battery.

 

No it will be fine. You don't "push amps" into batteries. They take what they will depending upon the charge voltage and the charge status.

 

If the engine battery is fully charged, it won't take much charge current.

 

Holding it at 14.4 volts for several hours while the domestics get charged up is not an issue. No problem at all.

 

Gibbo

[MoominPapa]

No it will be fine. You don't "push amps" into batteries. They take what they will depending upon the charge voltage and the charge status.

 

OK, thanks Gibbo. I'll wire it like that and stop worrying.

 

MP.