Monday, June 19, 2017

Electrical #2 Solar Panel

Now I have my nice & tidy double battery install under the middle cabin floor, I need a system for charging them. Little Cat is on a swing mooring so I cannot rely on shore power like most folks.

I use a Tohatsu 6hp outboard which has a 5 amp charging circuit. This is wired directly to the batteries (with a 10 amp fuse). The charging circuit seems to help, but doesn't provide as much juice as I had hoped. I think that the problem is that I mainly run the outboard at low revs (the Tiki does 5 knots at around quarter throttle), whereas the charger works best at high revs (as it would on a power boat).

So I figured that a solar panel could exploit all of the downtime that the boat is swinging on the mooring in the sun, and keep the batteries topped up.

Fabricating mounting frame from aluminum angle

I wanted something that would deliver at least 1 amp of rated charge and still be easy to handle. I bought a Coleman 20 watt solar panel that is rated at a bit more than 1 amp current in ideal conditions. The panel was not expensive (about $70) but once I started thinking about mounting it on the boat, I realized that buying the bits was the easy part.

The problems started with the wiring on the back of the panel. The terminal box that the cables come out of sticks out so far that that the panel won't sit flat. I wanted a robust setup so decided to fabricate a frame that would elevate the panel enough to give room for the cables underneath, and to provide a solid accessible mount for bolting to the deck

Finished frame.

I bought some lightweight aluminum angle stock from the hardware, chopped it up and attached it to the solar panel with stainless steel rivets. It doesn't take long to write that down, but all of that was quite a few hours of work (see pics above).

Now I had a solid and stiff mounting that would be rigid when bolted to deck or cabin and would protect the wiring underneath the panel.

The next step was the charge controller. I bought a Sunforce digital PWM (pulse width modulation) 10 amp controller for less than $30. This is not as fancy as a the more expensive MPPT (Maximum Power Point Tracking), but it is a multi-stage charger with a digital display of voltage and charging status.

Testing and adjusting the charge controller. The towel is to cover the panel. Note panel is without the frame/base.

I hooked up the panel to the controller and a spare battery to check that everything was working and found that the controller needed some setup as it was switching rapidly between float and charge modes. Thanks to the internet, I found a really useful post from someone who had already solved this problem by turning down the charge cut-in switch from a too-high factory setting (13.5 volts). With the help of a multimeter, I opened the case and made the adjustment down to about 12.8 volts (for the float charge cut-in) and have had no problems since.

OK. So now I could mount the components on the boat - but where? I had planned to permanently bolt the frame mount to the top of the cabin, but after mocking it up I could see that it was going to get in the way when under sail, as well as using up valuable deck space.

I finally decided to not bolt it down, but to further mod the frame for easy handling so that I could put it out on deck when moored, and stow it below when under way. Here the 20 watt panel turned out to be the ideal size, as it is small enough to fit in the cabin, flat on the floor when not in use.

Wired and sealed with heat shrink, cable is anchored to frame with zip ties, and the plastic cover/base is screwed on.

I used countersunk bolts to fix a 1/4" thick panel of lexan to the bottom of the frame. The idea is that this would protect both the panel frame and the boat from abrasion, and protect the wiring from too much moisture. Before bolting the lexan cover on, I sealed the cable connections with heatshrink and zip-tied a section of slack cable to the inside frame to act as a strain relief (see picture above).

Plastic base is fitted. Saddles for tie-downs are bolted to the frame corners and ready to go.

So, when the boat is on the mooring, the panel is out on the deck and has a couple of ties to saddles that are bolted to the frame/base. The cable runs to a connector fitting that screws into a waterproof socket on the cabin side. From the socket, the cable runs through the charge controller, which is mounted high up in the middle cabin (away from any water splashes), and then is wired direct to the battery.

The panel cable is wired to the plug (above) which can be quickly detached from the waterproof socket mounted on the cabin side. I needed a jeweler's screwdriver (from Harbor Freight) to tighten the very small screws in this fitting from West Marine.

I have had this system in place for about 5 months and am very pleased with how it works. It only takes a moment to put the panel out and plug it in, or to put it away. Using simple ties to keep it on the deck has worked fine in the high winds that frequent The Bay.

Charging and showing 13.2 volts. Controller is mounted next to the window in the middle cabin.

I had been initially concerned that a 1 amp charge rate would be too low to keep the batteries charged up, but I always find a healthy charge >13 volts when I get back on board for my weekly sail. All good so far.

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