by Prepper Doc
When the grid goes down, it is not a happy feeling if you have no backup power at all. Even a LITTLE electricity goes a long way. For most people I know, their first priorities are to have just a few electric lights, and then keeping the refrigerator from spoiling the food is next on their list. After that comes luxury items like A/C.
In a true end-of-the-world, where fuel becomes unobtainable, only solar power, hyroelectric power or other renewable electricity source will remain. Until you have that squared away (and a simple system isn’t that hard), having a generator or a battery-based uninterruptible AC power source (UPS) will get you through several hours. This article will focus on the battery-based system. They are especially helpful if you really didn’t want to run that generator all night long!
You can easily put together an uninterruptible power supply (UPS) that lasts far longer than the familiar computer UPS’s that run your computer for 15 minutes….just long enough to shut it down, basically. All of those system involve three components: a built-in inverter that can provide AC; a battery to run that inverter (automatically turned on when it senses the grid power disappeared) and a built-in charger that keeps the battery always ready to go.
If you have such a UPS, and if the battery inside of it happens to be 12 volts (which they often are) that certainly makes it easier– all you need is to add more battery staying power. Get a car battery – the Group 24 is often the cheapest per watt-hour – and simply connect it in parallel with the existing battery in the UPS, or even replace the UPS battery with the car battery. Use wire that is commensurate with the power level of your UPS– a 250 watt UPS can pull 20A from a 12 volt battery, so use 10- or 12-gauge wire. A 500 watt unit can pull 40 amps, so move to 6- or 8- gauge. Of course, if you pull that much power, you are going to exhaust your battery pretty quick….a typical fresh, fully charged Group 24 battery is about 75 Ahr, or roughly 800 watt-hours (at best)….and you really only want to pull half of that from it. So a few LED or CFL lamps would be fine (20 watts could be powered for 20-30 hours). You are NOT likely to be able to run your refrigerator from this computer type UPS – fridges pull 20+ amps of AC for a very brief startup interval…..which your UPS can’t provide.
You need a beefier charger to keep that car battery charged up than what is in the UPS. But you also want it not to boil away all the water in that precious battery. A modest-sized car charger that automatically slows to a trickle charger (most do that) when you aren’t using any AC power will do the job. If you basically never use that AC source, you could even us a timer to charge it only an hour a day. If you can get a cheap VOM from Harbor Freight, measure the voltage on your battery while your trickle charger is running – it needs to be around 12.8-13.5 volts for best life.
What if you don’t have a UPS? Not a problem. There are plenty of cheap 12-volt inverters that can produce anywhere from 75-400 watts of wall-plug type AC output. The inverters I’m talking about are NOT the $2000 solar-power-pure-sine-wave inverters; they are the simple quasi-sine-wave inverters that really put out a stepped square wave, and can be bought at the auto parts store or chain retail store for $30-$70. Connect one of these to your battery using appropriate wire. If you use one that is cigarette lighter-based, remember the center conductor is positive, and the side connector is negative. Or just purchase a socket, which will usually come with red (+) and black (-) wires.
If you want to simply USE that inverter to power the lights in one room of your house, no problem, just choose a charger that can put out some watts—there are usually ones about the size of a loaf of bread that can easily provide 60 watts worth of DC to your battery, where it will be immediately trans0ferred to the inverter and run the light in your room all the time. If the power goes out, you might not even know it! Of course, don’t waste electricity by using incandescent lights – get the far more efficient CFL or LED bulbs! Since the charger won’t really be CHARGING the battery (it will just be trickling it to keep it charged while most of the charger output really goes to the inverter), you won’t make any significant amount of hydrogen gas. I woudn’t lay a flame right on top of the battery, but other than that, no worries. You might put the battery inside a simple plastic tub in case any acid ever came out, however.
Trying to run the refrigerator is a much bigger deal. About the only want to really do that (in my experience) other than a generator, is to have about four car batteries wired in parallel, and use huge wire to go to a really capable 2000+ watt inverter….anything smaller is unlikely to be able to start the fridge. The “start” current (locked rotor amperes) can be 20 amps! The actual steady-state draw from a modern refrigerator once it starts is on the order of 150-200 watts, and they tend to run about 1/3 of the time unless your house is really hot. With four batteries, I could just barely get through a night in my experience.
I’m enclosing a photo of a very simple UPS built from a 75-watt cigarette lighter-type inverter, wired to a Group 24 battery, which is being continuously charged by a simple battery charter. You can see pretty much all of the wiring. Red on the charger goes to plus (+) on the battery, and plus (+) on the batttery goes to the red wire of a socket into which the inverter is plugged. From there it is just simple AC wiring.