Electronic Design and Family Site
My Radio Shack Solar Power System

For many years I have run about 10W of solar panels into a pair of 7.2AH gel cells to power my radio shed in case of emergency. This system served me well throughout that time except that the power wasn't available anywhere but the shed. If we had an extended outage, I couldn't power lights or a television in the house. Thus, I decided to make the batteries removable.

The first order of business was finding an appropriate case for the batteries. Since it was going to be away from the main charger unit, I needed metering built-in. This necessitated a case slightly larger than the size of the batteries. I searched for a case for weeks without finding anything appropriate; I even tried to build my own of wood...not quite what I had in mind. Finally, in a "Back-to-school" advertisement, I found what I'd been seeking, a 3L clear plastic case with a locking lid for less than $5. Into that I placed the two batteries, reverse polarity diodes, and an LED Voltage Meter, self-powered, so the batteries can power the meter directly. That comprised the block called "Battery Pack" shown in the wiring diagram below.

Originally,the overall charging unit not only contained the charge controller for the batteries, but allowed either the batteries or the AC power supply to run my station. I decided to remove the charge controller and batteries from the rig power wiring and connect them manually if needed.

Following a relatively recent Amateur Radio convention, I used Anderson Power Poles configured to the RACES standard for my battery connections. I used speaker terminals and spade lugs for the solar panel connection.

To house the electronics and seat the battery pack, wood seemed like the most logical choice. I built a shell out of 3/8" and 1/4" birch plywood, shown below. I won't go into the details of the construction of this chassis: if you know woodworking, it's very easy to construct. The faceplate is an etched PCB. I needed a relatively sparse faceplate, and constructing a graphics-intensive type like I would use for a radio or test equipment seemed excessive for such a simple device. Thus, I made a "white-on-Black" image in a graphics editor, transferred that onto a piece of FR-4, and etched the letters into the face. The substrate is very light in color, so I didn't clear-coat the copper. As it naturally corrodes, the letters will become more readable.
The first charge controller I used for many years was from an article by AA4PB, Bob Lewis in May 2001 QST entitled "An Automatic Sealed Lead-Acid Battery Charger". I ran that for many years until lightning destroyed it. I then tried a popular single-IC solution but discovered a fatal flaw in that IC: very high reverse current- if the input power is missing for any reason, the battery feeds back through the IC and quickly destroys it. So I moved on to a kit I found on-line by G. Forrest Cook called Solar Charge Controller for Medium Power Applications which led me to a very similar design, the SCC-3 by Cir-Kits. I laid out a PCB myself, bought a couple of parts, and made one...shown below:
PCB Layout Bottom View
PCB Layout Top View