I decided to add a solar charger my 1956 Chevy truck—a 2-ton flatbed used for hauling firewood and brush. It will hold five cords of wood in one load, and two loads is good for my year’s heating. I hope that after some better insulating of the house, one load will be sufficient. The truck gets used maybe six to eight days a year, so it spends most of its time just sitting. The starter battery tends to go dead after a few months, and I decided to do something about that.
I added an old 75-watt solar-electric module (late 1990s vintage, from an upgraded system), a deep-cycle AGM battery to replace the starter battery, and a Morningstar Sunlight-10 charge controller. This charge controller is a PWM charge controller and also has a built-in lighting controller, using the PV as the light sensor. We’ve used a number of these on driveway lighting systems; they can be set for various numbers of hours of light after darkness, or both in the evening and morning (it remembers when morning was the previous day and bases the pre-dawn activation on this). I’ve hooked the DC output of the lighting control to the input of a small (100-watt) inverter, which powers a string of LED lights around the top of the truck.
While I was at it, I added a Square D QO-series breaker box, since this truck had no fuses in it anymore. These breakers are rated for up to 50 VDC, so they work great on a 12-volt system. On a truck this big, it was no problem finding room under the hood to stick the box.
It’s not the most efficient scheme in the world, because, rather than optimizing the design, I used a lot of parts I already had. The charge/lighting controller was the only new purchase. The inverter has a cooling fan that runs all of the time, so it’s drawing around 4 watts by itself, about the same as the string of LED lights. The 75 W module is overkill for running an 8-watt load all night, though, so it works out fine.
Setups like this—usually with around a 5 W to 10 W module, and Morningstar’s tiniest Sunguard charge controller, if you were to buy new components—are very good for maintaining starter batteries on rarely used farm vehicles. The cost of a small module and charge controller is similar to a new battery for many tractors and larger trucks, so if it saves replacing the battery once, it has paid for itself. Of course, you can always take the battery out during the off-season and bring it into the shop for trickle charging. But having a module mounted on the vehicle is a much less labor-intensive way of making sure that old truck or tractor you keep out in the back 40 will start six months from now, the next time you need it.
Zeke Yewdall, Mile Hi Solar • Loveland, Colorado