Grid Powered Battery Charger - The Instructions
by Tom Woods from http://www.altenergyweb.com/gridcharger.htm
Grid-Charger Voltage Switch Materials
Be careful not to accidentally reverse the polarity of the 12 volt dc supply, or you will destroy the 78L05 voltage regulator. When connecting the LED, the flattened side should face away from pin 9 of the PIC. Observe caution and electrical codes when working with 120vac. Protect the PIC from static discharges.
After building the circuit you need to adjust the low and high voltage setpoints. You will need a voltmeter and an adjustable power supply capable of delivering from 10 to 15 vdc. Follow these steps:
The switch is now set to turn ON at the low voltage setting and run for a period determined by the two jumpers, from 1 to 4 hours. If the battery voltage exceeds the high voltage setting, the unit will shut off. The reset button toggles the relay ON and OFF, and the LED will blink to indicate the number of times the unit turned on since the last reset. To adjust the length of time the switch stays ON, change the jumpers on the board:
Once the adjustments are made you can connect the Grid Charger Voltage Switch to your system. Use small gauge wires to connect your battery bank to the battery terminals shown in the schematic. Use similar size wire to connect between the solid state relay control terminals and the pads labeled "relay" in the schematic. Make a power cable using #12 or #14 wire. Connect the hot (black) wire of this cord in line with the 120vac connections on the relay. Put a plug on one end of the cable and a receptacle on the other end. The relay, thus, becomes a switch allowing household current to pass or not, depending on the state of the relay. Plug the cable into a wall outlet. The other end will receive the chord for the battery charger. The photos below suggest one possible way you might choose to make the connections.
A Plug for a Really Good Battery Charger
My battery system consists of 10 12 volt batteries , 125 AmpHrs each. I chose the DLS55 charger made by Iota Engineering. These are excellent chargers, not the cheapest you'll find on the market, but they deliver precisely controlled current to your batteries. Mine has run flawlessly since I got it.
A finished assembly might look like this. Here, you see the orange power cord that plugs into a wall outlet. Harder to see, but coming out with the orange cord are two 18 awg cables that will go to the battery bank terminals. The outlet on the front of the box is the receptacle for the battery charger The red switch is the reset button and the white wall switch is an optional SPST switch to disconnect the battery power from the circuit board.
The metal box houses the circuit board, left, and solid state relay, right. Fastened to the cover plate are the switches and receptacle.
This is the grid charger voltage switch circuit built on a printed circuit board (available on last page).