charging both batteries A+B using solar

[OZ-Sailor]

I'm just about to install solar to my 25' Compass 750 and not sure how to set it up to charge both batteries (or if you can do this at all). I have two x 100ah 12v sealed batteries set up with isolating switch to offer battery 1, battery 2 or both batteries.

I just ordered this: 100 Watt 12V Solar Panels Kit + 20A Charge Controller for Off-Grid 12 Volt Battery System


As far as I understand I can only apply the charge to one of the batteries without setting up a similar isolating switch to swap between either battery, but can't charge both batteries at the same time

Is this correct?

[john61ct]

No.

While they are paralleled, they act like a single 200AH bank.

Not quite optimal with a switch in between, or if they are at different temperatures. But NBD.

More to the point are both the same model batt?

You could use a manual switch to combine for charging purposes, but a VSR / ACR would be better.

What is the reason for your split design?

[J.Kitchens]

If you connect the charge controller to one battery and turn the isolating switch to both you will charge both batteries. If you turn it to A or B you will only charge the battery that the charge controller is connected to.
If one battery is house and one battery is start I would connect the charge controller to the house battery.

[Uncle Bob]

Originally Posted by john61ct

No.

While they are paralleled, they act like a single 200AH bank.

Not quite optimal with a switch in between, or if they are at different temperatures. But NBD.

More to the point are both the same model batt?

You could use a manual switch to combine for charging purposes, but a VSR / ACR would be better.

What is the reason for your split design?

Or you could get a charge controller that will charge two banks independently.

[john61ct]

Please link to such a one, other than the Morningstar SunSaver Duo POS.

If that feature were actually required, which here it is not,

then a DCDC charger would deliver it more reliably and offer multiple other uses and lots more flexibility.

[john61ct]

Originally Posted by J.Kitchens

If one battery is house and one battery is start I would connect the charge controller to the house battery.

Yes, or whichever you use more frequently for deep cycling.

[J.Kitchens]

Or you could connect the charge controller to the Output terminal of the switch and then have the option of A B Both or None.

[belizesailor]

Originally Posted by J.Kitchens

Or you could connect the charge controller to the Output terminal of the switch and then have the option of A B Both or None.

None (off) = bad for most controllers...similar to throwing it to off with alternator spinning.

[john61ct]

Plus the output wires should have a chance of accurately detecting batt voltage on one bank.

[mvmojo]

Originally Posted by J.Kitchens

Or you could connect the charge controller to the Output terminal of the switch and then have the option of A B Both or None.

Originally Posted by belizesailor

None (off) = bad for most controllers...similar to throwing it to off with alternator spinning.

There's nothing wrong with connecting to the "output" of the A - B - BOTH - OFF switch, but best practice would be to also put an on/off switch from the panels to the charge controller. If you want to disconnect the batteries, switch the panels off first so they are not feeding the charge controller. Then switch off the battery switch. When turning things back on, switch on the battery switch first, then switch on the panels. The reason for this is that most charge controllers are powered by the batteries rather than the panels. Turning on the controller first allows it to boot it's software, configure itself, and get ready to control the input from the panels. You want to have the charge controller powered up before you switch on the feed from the panels. Likewise, you want to have the charge controller powered on when you switch the panels off to allow an orderly shutdown of charge regulation. To do this, you switch the panels off before switching off power to the controller. Rule of thumb: Power from your batteries to your charge controller is First On, Last Off.

[carlheintz]

Here's what I do when I put the boat up for the winter.... I have a small solar bank ( 15 w) and I use it to keep both house and starter battery charged. My plus side is connected to both batteries... so I have them in parallel. I run the solar directly to the batteries, and don't use any of the boat wiring. This is really simple... but it works. You don't need too much amperage. A 100 panel is way overkill. You had better have a good controller in between the battery and the solar panel, or you will overcharge the batteries.

[NevisDog]

Interesting thread with very useful info, thanks. One option not yet mentioned is the Votronic range of controllers (from Germany, there may be other makes) that charge the house bank while also trickle-charging the start battery. Simple to install and I've had no problems since installing about a year ago.

[ebsail]

I do what carlheinz does. Both of my 2 group 24's are connected to a 50 watt panel with a simple controller with the master on both, all winter. Keeps everything charged. I do the same when I leave the boat on the mooring during the summer. So far the batteries are fine for the last 5 years.

[J.Kitchens]

Originally Posted by belizesailor

None (off) = bad for most controllers...similar to throwing it to off with alternator spinning.

I have personally checked this on numerous (not all) charge controllers with no ill effect. I know for a fact it will ruin an alternator but an alternator is a completely different beast than a charge controller.

[joehixon]

Can you leave your solar charge controller connected while the engine is running the alternator?