Hi ,

Does anyone have a very simple circuit for charging (2) 12 volt marine batteries (approx 100 amp hr.each) from a single 15 watt solar panel and maintaining isolation between batteries ? Thanks for any help you can provide.

silverirv

 

Due to the high capacity of the batteries and the relatively modest solar panel output, I would just connect the panel to the batteries via a 3A diode per battery and see how it goes.

 

Blocco's suggestion isn't bad.

Shottky diodes will have far less Vf (forward voltage, or voltage loss) than standard rectifiers will.

Overcharging batteries will damage them. You will need a method of determining when the batteries are charged, and to cut off the charge current - or clamp the maximum voltage.

 

It all depends how much voltage you are prepared to drop.

Depending upon the expected current draw the use of rectifiers (even Schottky) can produce a significant volt drop. These days the trend is to use P-chan mosfets as the most efficient method of control.

If you can tolerate a small voltage drop then a simple arrangement such as this will suffice
http://www.rverscorner.com/info/diode.html

Dave Johnson has produced a fairly simple circuit using a couple of IC's, some P-chan mosfets and a couple of resistors, if you want the least voltage drop.
http://www.discovercircuits.com/H-Corner/bat-iso.htm

 

You are not going to charge two Deep Cycle 100Ah. marine batteries from one 15W solar panel(this rating usually given at full miday sunlight). Especially if the batteries are connected to the boat and are in a marine eviroment. Also the natural discharge will be more than you can provide. You will need 6.6 days of full power (at 24 hours of full sun a day) to fully charge both batteries that is without the consumption of your regulator and without the natural night discharge, bilge pump,etc.
As a personal experience with marine batteries I have found that there are certain conditions that can make marine batteries lose a lot of charge depending on the temperature and amount of charge stored when left and other marine air conditions. Also depending if I let both switched in parallel. I think it will be better to let the switch off or on a single battery before leaving. Sometimes I could not start my boat after a few weeks and I had to charge the batteries. I was using two deep cycle lead acid 180Ah. and had two 355ci. 6 cylinders straight Diesels engines. I suggest gell type batteries or AGM.
This is an amp hour calculator.
http://www.rpc.com.au/products/services/faq-info/calc/calculator.html