Adding solar power to deer deterrent
The battery
powered deer deterrent started slowing down yesterday, which
prompted us to tinker with the idea of charging the battery with a
solar cell.
If you take apart one of
those solar powered garden lights you'll most likely find a AA battery
with a circuit board.
I'm guessing the electronic
parts prevent the battery from being over charged. I know the amps are
different on a D cell compared to AA, but I thought it was worth a try due to the fact that both batteries put out the same 1.5 volts.
The modification was simple. Just pull out the metal battery connectors
with pliers, strip the ends and thread each one through the hole where
the screw usually fits. Snip off the plastic portion where the screw
bites into and then you'll be able to put it back together with just
one screw and the other two deleted.
The other end of the wires get hooked up to the D cell battery.
Drilling a 3/4 inch hole at an angle allows for easy mounting of the
unit while optimizing the solar angle a bit better than just having it
point straight up. I'm thinking the LED light that comes on at night might need to be bypassed to save more juice for deer deterring.
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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.
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I hope it works, but I have doubts that a AA will last all night long, or recharge fully. Hopefully I am wrong.
Maybe you could wire two or three units in parallel so you will have more capacity?
If you know the size of the solar panel and the power draw of the motor, (assuming an irradiation of around 1000 W/m2 unless you have better local data and an efficiency of the panel of 10%) you can calculate how many hours of sunshine you would need per day to keep the battery topped up.
But a simple experiment is to remove the battery when the sun is shining. If the motor still turns, it's OK. If not, it won't work because the solar panel cannot produce more energy than the motor consumes. And given the fact that you want the motor turning 24/7, the panel should be able to produce way more than the motor consumes.
Additionally if you have an amp meter, you could measure how much current the motor consumes versus how much the panel produces. That would give you a much better picture of the real power of the solar cell.
Eric-I was just telling Anna that we might need to add another solar light. Wiring it in parallel feels like it would double the amps if I can remember my Ohms law correctly. Another factor I didn't mention is that the battery in question is Alkaline, non-rechargeable, and nearly depleted. Not a fair test, but I thought there was little to lose.
Roland-I like your idea of hooking up a solar cell directly when the sun is full to see if the power is enough. The solar light in question only cost 3 dollars at the local discount store, which most likely means its under that 10 percent rating you guessed at. Measuring Amps with an Amp meter is something I've struggled with in the past and still remains an esoteric skill like measuring the value of a capacitor or taking a picture of Bigfoot.
Mark, if you have a multimeter, measuring DC current is simple. Most multimeters can measure DC voltage, AC voltage, DC current and resistance (but not impedance). AC current is usually measured differently, via an induction clamp around the wire. Some multimeters can measure the capacity of condensators.
You just have to remember; if you're measuring DC current, the multimeter has to be part of (in series with) the circuit. If you are measuring voltage, e.g. over a motor it has to be parallel to the motor. Relatively straightforward. You have to put the multimeter in the correct setting, though.
N.B, most alkaline batteries are not rechargable! Doing so anyway may cause them to rupture or leak caustic potassium hydroxide.