Solar panel and multiple batteries. OK?

[NPMR]

I have installed a solar panel on the new boat. With simple controller.

I have wired it directly (with fuse) to the main domestic battery and all the LED's lit up as they should, implying that all was well.

But waking up in the middle of the night, I wondered if this was true.

I have 3x70Ahr batteries wired together with some fancy charger, for when plugged into the mains etc or, I suppose, when the engine is running.

There are 4 x battery switches - 1 x black (marked negative) and 3 x red ones. Each battery is separately brought into action and none work until the black switch is operated. The system is 1 x battery for engine. 1 x for main domestic and 1 x extra for domestic, in paralell I think.

My objective was to boost the main domestic battery when off the boat. But my sudden unease in the night was to wonder what happens when they're all brought into action, when out sailing or motoring. Will the solar panel be trying (and obviously failing) to charge all three batteries?

Is this a job for an electrician, or actually, is it as simple as I first thought?

 

[VicS]

I have installed a solar panel on the new boat. With simple controller.

I have wired it directly (with fuse) to the main domestic battery and all the LED's lit up as they should, implying that all was well.

But waking up in the middle of the night, I wondered if this was true.

I have 3x70Ahr batteries wired together with some fancy charger, for when plugged into the mains etc or, I suppose, when the engine is running.

There are 4 x battery switches - 1 x black (marked negative) and 3 x red ones. Each battery is separately brought into action and none work until the black switch is operated. The system is 1 x battery for engine. 1 x for main domestic and 1 x extra for domestic, in paralell I think.

My objective was to boost the main domestic battery when off the boat. But my sudden unease in the night was to wonder what happens when they're all brought into action, when out sailing or motoring. Will the solar panel be trying (and obviously failing) to charge all three batteries?

Is this a job for an electrician, or actually, is it as simple as I first thought?

Difficult for anyone to answer precisely without knowing what your " fancy charger is " or how things are wired together.

You need to find out what your "fancy charger" is. You may be able to find instructions for it on line if you have mislaid the original . Or post the details on here for help. You need to find out if it has several outputs or just the one and how it is wired to the system.

Your black switch is in the common negative connection to all the batteries ... it disconnects the negative from all the batteries.

You need to check that you are correct about the three red switches.......... are you sure that one does not parallel engine and house batteries for emergency use.

You need to check the details of your solar regulator ... how many outputs and how connected/divided between the battery banks... how have you connected it?

You need to establish how the alternator output is split between engine and house batteries....... fancy dual output controller, diode splitter or VSR

 

[GrahamM376]

From what you say, if all your switches are off, the panel should only charge the bank the regulator is connected to and this can easily be checked with a voltmeter. Doubtful if the battery charger will create problems as, all multiple output ones I have stripped are just single output with split charge diodes feeding the various battery banks, therefore they won't parallel batteries.

 

[ghostlymoron]

You need to check that you are correct about the three red switches.......... are you sure that one does not parallel engine and house batteries for emergency use.

I've commented before that I don't think that paralleling the batteries for emergency engine starting is a good idea. If you parallel a battery with 12.7v output with a battery with 11.7v output you'll only have 12.2v which may not be enough to start your 'donk' - better to just use the one with 12.7v on it's own or you could end up with two battery banks that are incapable of starting your engine.
Regarding solar charging several batteries, provided the output from the panel is above the voltage in the battery, power will flow to the battery. Most solar panels have built in diodes so cannot come to harm from back feeding from a battery charger. It all depends on the way the batteries are connected. If they're all isolated by diodes or isolators, power will only go to the one directly connected.

 

[VicS]

I've commented before that I don't think that paralleling the batteries for emergency engine starting is a good idea. If you parallel a battery with 12.7v output with a battery with 11.7v output you'll only have 12.2v which may not be enough to start your 'donk' - better to just use the one with 12.7v on it's own or you could end up with two battery banks that are incapable of starting your engine.

Absolutely. it is better to be able to parallel the circuits than the batteries by connecting a paralleling switch "down stream" of the isolators. That way a dead battery can be left out of service and the good one used for all.