Even after I upgraded all the cabin lighting on the boat to LED lights last year I was still finding that on longer trips the batteries were running down and that the outboard engine did not recharge them fast enough to replenish what was being used. I realized that I needed a solar panel to keep the batteries charged up. I didn’t need anything too large, my battery bank is only about 145AH, and the boat does usually spend the whole week sitting at the dock with almost no load on the batteries. I really don’t mind if it takes the whole week to recharge from a weekend of usage, as long as there is enough battery capacity to get me back out and back the next weekend.

Having already determined that the largest panel I wanted to fit on the boat was going to be a low wattage panel, and without doing much more research on the matter I picked up a 5W Sunforce solar panel and 7A solar charge controller, as well as a Sunsei solar panel mount at the West Marine Spring Sale, and installed the charge controller this spring before launching the boat.


Sunforce 7A Charge Controller Installed

Sunforce 7A Charge Controller Installed

Before I got a chance to install the panel I was at the Defender spring sale where I found the Ganz 12W Marine Grade solar panel which is only an inch or so wider than the other panel. Aside from being nearly 2.5 times more powerful, it is also noticeably better constructed, and designed for the marine environment, not to mention it weighs less than half the weight of the Sunforce panel. It was a no brainier, and I purchased the Ganz panel and returned the other panel to West Marine.  Enough about the panel for now, details on the installation are located here.

A few weeks after getting the panel installed I noticed that the built in hydrometer on one of my batteries was only registering a charge state between 50-75%, even though the charge controller had been showing the batteries were fully charged for at least a week. This confused me as I knew that a hydrometer was one of the most definitive and accurate ways to determine charge state in a lead acid battery, so I started doing the research about charge controllers that I should have done at the beginning of this project, and I found that not all charge controllers are created equal. I won’t go into the long details about the differences as it was recently explained very well by Maine Sail on the SBO users forum here, but the short version is that the cheap sunforce controller was shutting off the solar panel at the critical 3rd stage of charging, and preventing the batteries from ever taking a full charge.

While doing this research I came across the amazing little Genasun GV-4 three stage MPPT charge controller, the only MPPT controller currently on the market designed specifically for low wattage solar panel installations, and promptly purchased it.  Installation was simple, I just had to make up a new set of wires to go from the battery to the controller as it just has a set of terminals to connect to, where the old controller had built in (non tinned) wires attached. I used  Ancor 16ga tinned marine wire, with heat shrink sealed ring terminals on the end attached to the battery.

Genasun GV-4 Charge Controller

Genasun GV-4 Charge Controller installed

By the time I got to the boat during lunch a couple days later to check on the batteries, the batteries were fully charged sitting at float stage, and the hydrometer was indicating a full charge, Success!

Shortly after completing this I found out that the charging circuit on the outboard engine was unregulated. Details from that project are here.

Continue on and read about the actual solar panel installation

3 Responses to “Solar Panel Charge Controller”

  • Mike says:

    Thanks for posting your battery project. I see what type batteries you used. Sealed, wet, Gel. I went to the site for the Genasun controller but didn’t see a low voltage disconnect in the specs. I’m setting up a small 22′ boat and doing a little looking around before buying a controller. LVD is one of my criteria and the Genasun may not have it. Can you tell me if it shows in your installation manual? I don’t have the battery bank you do and am using a gel battery which doesn’t like anything over 14.2vdc and under 10.4.


    • I am just using 2 regular flooded wet cell deep cycle batteries for a total bank size of 160AH. I don’t have the ability to charge fast enough to warrant upgrading to anything else, my power needs just are not that huge. I’m not sure what you are trying to figure out with the LVD, but the Genasun controller will shutdown if the input voltage is too low to continue to provide a charge to the batteries (like at night), and indicates this by a momentary blink of the LED once every second or two. I have never had an issue with it, and while the controller does draw a small phantom load from the batteries over night, it is VERY small (0.9mA), and as such could sit there for months with zero solar input before it results in any real discharge from the battery bank. If you are worried about what the controller will do when the batteries get below 10.4v, you should be looking at a larger panel, and/or a larger battery bank since that means you are fully discharged the battery well beyond where you should have. I think you’ll be quite happy with the controller, I hardly give my batteries a second thought anymore, I know that whenever I walk down to the boat they will be topped off and ready for whatever I intend on doing, and that throughout the day if I’m using power, at least part of that is being supplied directly by the panel and not drawn from the batteries, so I’m extending the battery life at the same time I’m using them by having the solar there.

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