I’ve built a few charge controllers, half of them are built from scratch. All but one were placed in home-made aluminum clamshell cases, and two of them are shown here.
The first one is from an article in August 1980 QST Magazine, and was designed by Douglas A. Blakeslee, N1RM and shows up on page #12. This charger uses any large pass transistor in the 2N3055 family as a series switch to allow current to flow from the solar panels through to the batteries and rigs. I used a smaller 2N4912 unit which allows up to 7 amps of current to pass through, although I don’t plan on putting more than 50 watts through it. I wasn’t planning to use a 100-watt panel to supply this, as my battery was much smaller and I don’t have any hi-powered rigs to run. The front panel acts as a heat sink and is in contact on one side with top and bottom panels to dissipate excess heat. You can see the phono plugs I use to connect the input and outputs with, and the board was scratch-built with a dremel tool to cut the traces.
The next charger is from the June 1994 edition of 73 Magazine and is called The MRP4 Solar Charge Controller by Mike Bryce, WB8VGE. It is an excellent charger for gell cells and, unlike the previous charger I built, uses a shunt configuration to turn on/off the charger. Here also I made my own board and, although I mostly stuck with the layout provided, I did make two minor changes by swapping the designer’s 3-amp blocking diode with a larger 6-amp diode and using an A/B mini-pot in place of the on-board trimmer the layout provided. I wanted to be able to adjust this from the panel, although I can’t recall why. I think it had to do with differences in various manufacturer’s specs regarding charge voltage. In any case where you need to know what voltage to charge your batteries up to, ALWAYS go with the manufacturer’s recommendations over any generalizations provided by other “experts”. The maker knows their batteries better than any outsiders. Since the original design called for a 3-amp blocking diode, I’m assuming this charger will handle 3 amps of current, which is plenty for my purposes, and using a larger diode ensures It won’t blow. I have no idea why I wrote “4” amps on it. The 30-40 watt panels I intend to use will send between 2-3 amps of current through these units, which is plenty for most QRP operations.
You’ll notice both of these chargers are housed in my typical clamshell cases. Here, I used a thinner sheet metal for them. I believe it’s 20ga for the tops and bottoms instead of the usual 16ga., and 18ga for the front/back panels. This is much lighter than my usual cases and still plenty rugged for field use. The completed chargers weigh almost nothing, although they do take up 15-20 cubic inches of space each.
I should point out that Mike Bryce also made another charger called “The Micro-M”, and I have one of these I installed in a plastic case I got from the now-defunct Radio Shack. It is also an excellent unit and quite perfect for backpacking with most QRP-related gear. You can look it up in September 1996 issue of QST. I got my board and kit from Mike, but I don’t know if he is still selling any of these units, or if the boards are available from FAR Circuits. It’s been a number of years, and he may have moved on to other products.