One of the most important considerations when choosing which portable generator to buy is what size you need. Buy one too large and you are wasting your money both on the purchase and on the fuel to run it. Too small, and you may burn out your appliance motors. So, how do you determine the right size? Each appliance and each generator will be rated for a running voltage and a starting or surge voltage. Some motors require much more power to start than to run, possibly 3 – 4 times as much. The surge voltage of the generator needs to be able to handle the start voltage of the appliances you hope to run. It is not necessary for it to cover all of the start voltages of all the appliances at once, if you plan to start them in some sort of staggered fashion.
To calculate the size of generator you will need, look at the label on the appliances or tools you plan to run with your generator. You will need the basic physics equation of Watts = Volts x Amps. Appliance labels will give you at least two of the three, so you can calculate the other one. Generators are rated by watts, so you may need to do some number crunching to get everything into watts. To run an incandescent light bulb, for example, you would just use the wattage stated on the package as the contribution from the generator needed for that light bulb. For other tools, you may need to calculate. For example, a battery charger that runs at 15 amps and requires 25 volts would need wattage of about 380 to power it.
Another consideration is how you want the power delivered. Some generators do not allow you to take all of the power through one outlet. Make sure you have enough watts available through at least one of the outlets to power your biggest appliance or tool. Many smaller generators are designed to run on gasoline, many larger propane generators are designed as a permanent back-up power supply and not portable. Examples of starting watts needed for some common household items are below:
Coffee Maker: 600 Watts
Electric Range (one 8″ element): 2100 Watts
Clothes Dryer: 6750 Watts
½-HP Sump Pump: 2150 Watts
10,000 BTU Air Conditioner: 2200 Watts
1HP Pressure Washer: 3600 Watts
Desktop computer: 700 Watts
Monitor: 225 Watts
Printer: 500 Watts
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