How to Build a Low Budget Emergency Power Supply

The first thing you need to think about when working with electricity is safety. If you are under age you should not try to assemble high power devices without adult assistance. For those who like to dabble this is an extremely simple assembly and can be heavily scaled and customized to your own needs. After taking all safety concerns into mind and getting all the protective gear you need to work with batteries and electricity, you must then figure out what your power requirements are actually going to be. For most small appliances like an AM/FM/XM radio or a medium to small television you most likely won't need any more than 200 watts per device. If all you want is a lamp and a radio for an hour or two while waiting for a storm to pass or a blackout to end then a 400 watt system will probably be more than you need. The reason to select the lowest wattage output you can get away with is because the higher the wattage the faster your battery will be drained.

I personally use an 750 Watt inverter. After you determine what power level you need you need to acquire the inverter of the appropriate size. Inverters range from 75 on up to 6500 watts and beyond. The chances of finding over 1000 watts on a store shelf is pretty slim the really big inverters need to be ordered and the price tag gets pretty big over 800 watts. Only because they are a national chain that everyone knows of, I will mention that Wal-Mart has Inverters of several sizes for relatively low cost. Autozone and other car parts stores carry them also. When selecting your inverter you should look for one that comes with optional jumper cable type connectors. However if you only want a simple 75 watt backup device for a small net book than you will have to procure an after market accessory socket. The basically look like a cigarette lighter socket in a car but come without the lighter itself.

For this article I will first describe the parts and construction of my own backup power supply. I first purchased the largest inverter I could find in my town which was a disappointing 750 watts. I then stopped at Sam's Club and bought a cheap plastic toolbox that I thought the battery I had chosen would fit in. After realizing I'm not as good at eyeballing things as I thought I was I cut the tool tray down and mounted the inverter to the remaining portion of the tool tray. For the mount I just drilled four holes in the edges of the silver plastic cover and put four screws through right into the tray. To the left of the tray holding the inverter I put a top post terminal 1000 amp 12v truck battery. I did not bother putting in rubber mounts for the battery but if you plan on moving the device around frequently or storing it in an area prone to vibration it would be a good idea.

Permanent rubber mounts will prevent anything from boring through the plastic wall of the battery from friction or repeated sliding. The Black & Decker Inverter that I ended up using came with a jumper cable type connector so I did not need to purchase the lead clamp connectors or extra wire. If you do not have this type of connector with your inverter you can get the battery connectors at your local auto parts store. Most of the larger inverters seem to have thumb screws rather than requiring specialized cables. This will make adapting your wiring much easier.

After I hooked up the power cables to my inverter I decided to add an outlet to the front of the toolbox. I simply used a dremel to cut out a square hole and then spent a moment trying to make at look as pretty as possible. I then lined up the outlet and drilled screw holes. I then used machine screws with nuts to fasten the outlet in place.
Since the six outlet square I had chosen was designed to plug into a regular two outlet socket I just used two cheap short extension cords and plugged it in to the inverter via the extension cords. Were this a much larger inverter this might prove to be a problem as the small brown extension cords I used aren't designed for huge loads but given the size of the inverter I am using the circuit breaker on the inverter will trip before the extension cords ever got warm if I tried to plug too many things in. Before you begin using your new portal AC system be sure to give the battery a good charge with an automatic battery charger. I bought a twenty dollar charger at Autozone and keep it right inside the box under the inverters tray. Once you have your inverter and battery of choice fastened into the toolbox and have completed the first charge on your new battery you are now ready to frivolously waste your battery's charge. You should see how long it will run with a full charge so you aren't caught by surprise if the load you are using it for drains the battery faster than you expected. If you bought an inverter with battery protection you may notice it making an annoying squealing sound after two or more hours. With all my inverters at least, that means the battery has dropped below 10 volts. If your inverter doesn't have protection circuitry things tend to break so be glad if you have it.

For someone who simply wanted a portable or emergency backup around the 100 watt range can get away with a small 12v sealed lead acid battery like the kind used in children's riding toys. With these batteries though you generally need to change the connectors and buy a specific charger for the battery. Another benefit is the reduced weight, large truck or RV batteries makes it less than pleasurable to carry around. You can actually make a 100-200 watt model in a pretty small tackle box with the right sized components.

There are some problems the most obvious being the limited run time. Unless you have your device wired into some kind of wind or solar charging circuit you will have to recharge them after the power comes back on or from another 12v source. However it can be quite useful having 2 hours of electricity that doesn't use oxygen or make noise and exhaust fumes. You would be able to monitor emergency radio or TV while the kids sleep even if you live in an apartment. I would not advise however keeping vented or spill-able batteries inside your home, you should use a sealed battery. Spill-able batteries can be dangerous to the occupants as well as a possible fire hazard. When making a backup power system remember the device itself should be kept dry and well ventilated and you must never plug it into or try to connect it to another power grid or system. When it comes to AC you can't just splice wires together between inverters or wall outlets. The problem is the different AC grids will be at different phases and will most likely cause a flash, bang and a hole in something if you attempt to bridge them. If you are interested in getting off the grid or looking into supplemental energy this is not the way to do it. You would be better off getting a professionally installed system with proper inverter/phasing equipment.