Solar Charging Batteries in Parallel

[Captain Dighton]

I have 2 12 volt marine batteries in parallel and I am looking for a solar charger to charge them. Battery number 1 is a Duralast 12 volt (Marine cranking amps 685, cold cranking amps 550, amp hours 85, reserve capacity 140). Battery number 2 is a West Marine Duravolt 665 MCA (cold cranking amps 685, reserve capacity 90. I took this info right off the batteries.

The solar charger I had last year seemed to maintain and not charge. The handheld battery meter would read 8.9. When I plugged them into a battery charger from the dock they would read 12.4. My problem is I am on a mooring and not a dock. The boat is used primarily on weekends and sits moored during the week.

Please forgive my electrical ignorance as I don't know a watt from an amp. Is there a solar panel that will charge these batteries? If so, can someone recommend a size (watts / amps) and will it need some sort of a regulator so that it does not over charge?

Thanks for your help.

 

[Mike B1026]

Do you have a battery selector switch? "A or B / A & B / OFF"? I'm assuming you don't since you mentioned them parallel.

You also need to know how much you drain the batteries over the weekend. so you know how much to put back into them over the week it is sitting on the mooring. Check the voltage at the end of the weekend. You can then calculate how many amps you need to put back in. Get some numbers.

They do make controllers that are designed for two batteries.

example:http://www.morningstarcorp.com/en/sun-saver-duo

(I don't sell controllers but many of my customers like these.)

 

[mitiempo]

Any panel large enough to charge batteries after use rather than maintain them at full charge will need a controller.

If your batteries were 8.9 volts that was a life shortening event. 10.5 volts is considered a dead battery.

The 12.4 volts you measured under charge was also too low. If on a charger the batteries should measure 13.4 - 13.5 on float if fully charged and about 14.4 volts if bulk charging.

A 40 to 60 watt panel with a basic controller like the Morningstar Sunsaver 6 amp controller (about $60) will work fine if the batteries are in parallel as you say - in one bank. If they are in 2 separate banks as they probably should be if they are different sizes the Sunsaver Duo is a good controller and has as an option remote monitor that gives you the amperage in or out on a digital display. About $125 basic and $200 with the monitor.

 

[rgranger]

Isbn: 9780071462846

You need Don Casey's

"Complete Illustrated Sailboat Maintenance Manual"

There is a complete chapter on boat electrics and it talks about solar panels, chargers, regulators etc. It assumes you don't know an amp form a watt so no worries. It will walk you through it and then you will know the difference.

I think he may have published the electric chapter as a separate book but I recommend getting the complete set in one book.


I have a copy and reference it regularly. There is all kinds of good stuff in there.


One thing that stood out in your post was the fact that you are using two different types of batteries. That is a no-no. The batteries will "fight" each other.

 

[tommays]

I did a 40 watt panel mounted Mainsail style

With a small genasun GV4 control

The system peaks out at 2.7 amps and as soon as there is any light it puts out about .3 amps and as the day passes it peaks at 2.7 and then works down to .3 again

It is wired to the house battery and after bringing it up the ACR turns on and the cranking battery gets taken care of

In general it seems to have no issues with two group 27s that get used on weekends