Monday, August 18, 2014

Using a Solar Panel to Keep a Generator Starter Battery Charged

Just a quick post this week.  I thought I'd do an update on the solar project I'm doing for my father.  There isn't anything too complex involved, just a solar panel connected to a charge controller that keeps a battery topped up that's used to start a back up generator.  The generator is used infrequently and the battery has a habit of being flat when needed.  The generator is in the shed that the solar panel will be mounted on. so installation is pretty easy.  To make the project more interesting the load terminal of the charge controller was connected to an LED light to give extra light at night and indicate the condition of the battery.

My previous testing of the MP-3720 solar charge controller can be seen here.

The charge controller was mounted to the frame above an unused door.  It's not an ideal place, but any higher and it would be too close to the hot corrugated iron roof.  The kind of heat involved would significantly reduce the life of the controller.

Solar Charge Controller
Solar Charge Controller
As the installation was unplanned, I was flying by the seat of my pants.  The solar panel, battery, LED light and charge controller wiring was bought together in the best way I could.  With more time and planning I could have done a neater job, but you work with what you've got, and what I had was a strip of terminals.  I plan to revisit this and make it neater, but it does the job for now.

Wiring (don't look at it, it's shocking I know)
The LED light was an afterthought, the terminals were there and a small light in the backyard at night seemed like a good idea.  It also serves another purpose, it indicates the condition of the battery.  The light only comes on at night and will only come on if the battery voltage is above 11.5 Volts.  If it doesn't come on it shows that there's something wrong with the system.

Solar Panel and LED Light
LED light connected to the solar charger
There are still a few things to tidy up, but the job is almost done.  I have a high current switch on order that will allow the battery to be switched between the solar charge controller and the generator.  It may not be absolutely necessary,  but I didn't want to start the generator while the charge controller was connected to the battery.  The starter motor draws a lot of current, and where there's large current into an inductive load there's the possibility of voltage spikes caused by inductive kickback.  Yeah, I could come up with some kind of snubber circuit, but this is simple and foolproof.

Solar Panel
Solar Panel

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