Uninterrupted Power Supply
Our UPS (Uninterrupted Power Supply) is pretty straight forward. The components are readily available and anyone with a little electrical savvy can assemble it from the schematic we drew. We assembled the relays, fuse, inverter and Sure Charge on a piece of plywood mounted on the wall next to the fencer with the battery on the floor.
Relays (shown as #1 & #2) - We bought two DPDT, 120VAC coil, 10 amp contact, plug-in relays. These relays are enclosed so dirt, bugs and fingers wont mingle with the electricity. They are a general purpose relay available from Grainger (either square or octal base by several manufacturers), Radio Shack (#275-0217C) and many other suppliers. We also bought sockets for both relays.
10 amp fuse - This fuse protects the inverter if something goes wrong. We used a 3AG fuse and had to get a fuse holder for this type fuse.
Switch - The system needs to have a switch to turn off the fencer while we are making repairs to the fence. Unplugging the system from the wall or shutting off the power to the system will only turn the UPS system on; we need a switch on the fencer circuit itself. A 10 amp (minimum) SPST switch, wired into the hot wire to the fencer, worked fine.
Battery - We use a large marine or deep cycle lead acid battery. The size and capacity is similar to the battery in our truck but deep cycle batteries are designed to be rechargeable even after being completely discharged. That can happen during a prolonged power outage.
Sure Charge - Lead acid batteries lose a lot of their capacity if they are not used regularly. As a backup system power supply, this battery will just sit there, doing nothing, until the power goes out. In order to keep the battery in top form and ready to go, we use a SureCharge auto-float control. Battery float controls are available from most auto supply stores and a myriad of catalogs.
Inverter - This guy converts the 12VDC from the battery into 120VAC for our fencer. Most fencers dont draw much power so the smallest inverter we could find works fine; we use a 125 watt inverter we bought from a camping supply catalog.
Fencer - We already had this so we incorporated it electrically into this system. We wired in an outlet where the fencer is shown, on the schematic, because we didnt want to cut the plug off our fencer and hard wire it into the system.
Miscellaneous things we had to consider - something to mount everything on (like plywood), sockets for the relays, a holder for the fuse, a connector or outlet for the fencer line cord, a line cord to plug the whole system into our AC power source (the outlet on the wall) and some 16 gauge hook up wire (lots of different colors made tracing wires easier). We built a tiny shelf on our mounting board for the inverter.
We knew the assembly MUST be kept dry and well ventilated. A cover to protect your UPS from curious fingers is not a bad idea because there are voltages that can kill a person but we had to be sure that the inverter has plenty of air circulation to keep it cool.
We hope the above explanation of what we use for our UPS will be helpful when planning your own system.
We used this system successfully for quite a few years. However, we live way out in the middle of nowhere and our power goes out frequently, sometimes for several days. So, it became necessary to install a backup generator for power to the fencer as well as everything else. Therefore, as well as it worked, we no longer use this UPS system.