The recent windstorm and resultant power outage underscored the need for emergency preparedness when the lights go out. We were without power for a couple of days; others around us were out even longer. Besides being inconvenient, outages can become expensive when the food in your refrigerator spoils. Having a portable generator is a good idea in these situations. If you think it’s time to buy one, here are a few items to consider.
What size do you need? To figure out that answer, list the items you want to power with the amount of power (or current) they need. By law, each appliance will have a label listing its input power requirements in volts (V) and watts (W) or amperes (A or amps). The volts will all be around 115-120 VAC, but the watts or current (amps) will vary from item to item. To convert amps to watts, multiply by 120 V.
For example, I want to run my garage refrigerator (120 VAC, 4.5 A), a laptop (0.6 A), a few lights (100 W), and my microwave oven (1700 W). First convert the refrigerator and laptop to watts: 120 x (4.5 + 0.6) = 612 W. Add in the light and microwave for a total of 2412 W.
This is the minimum size my generator needs to be. However, whenever an appliance first turns on or starts up, it uses a lot more electricity. This is commonly called surge current. Generators will list Maximum power as well as Continuous power. If you exceed the generator’s maximum power during the initial surge, you will trip the breaker on the generator. Surge currents are hard to know because appliance labels often do not list them. I did find that my garage refrigerator has a surge current of 10.2 A, well over two times the running current. To be safe, get a generator with a continuous power rating that is twice your calculation. Note that if you plan to run a microwave oven with the generator, you should triple the power because microwaves have enormous surge currents.
A typical size generator for this type of use is in the 3000-watt to 5000-watt range. Prices for these will start around 10 cents per watt and go up to approximately 15 cents, depending on features.
What about connections? While having enough power is one requirement, connecting your appliance to the generator is another. Portable generators usually have two or four outlets built into them for plugging in extension cords. While you can add a power strip to get more outlets, only use it for small electronic items. Keep kitchen appliances on their own extension cords. This may present a problem for any built-in appliances in your kitchen, like microwaves and refrigerators. You will need to talk to an electrician about getting those wired up for a generator connection.
Where should it be placed? A generator produces exhaust, so only run it outdoors. It is also quite noisy, so figure out where you will keep it ahead of time. Realize that you will need to run extension cords from it to your appliances, so be sure to have appropriately sized cords. Do not connect a bunch of short cords together; they are not rated for that. It is also essential to protect the generator from rain.
What about fuel? Most generators are gasoline-powered, but there are dual-fuel units that will also run on propane. While the propane option is more expensive, it provides a long-term fuel storage solution. Unlike gasoline, which goes bad in a few months, propane can be stored indefinitely. If you are only using your generator for emergencies, it may go months or years between uses. Be sure to run all the gasoline out of the generator before putting it away so you won’t have to purge out old gas the next time you need it. If you opt for a propane unit, you must realize that propane produces less power than gas, so you will need to derate the listed power by 15%.
How do you want to start the generator? Consider if you want an electric start or manual start. If you’re in good enough shape to use a pull cord, you can save some money. Otherwise, there are electric start models available.
Most importantly, if you decide to purchase a generator, set it up and test it all out before you need it. It doesn’t help to have a generator still in its box when the lights go out!
Walt Caldwell is a product development engineer with over 35 years experience in aerospace, medical and consumer electronics industries.