Power Sources

Getting back to the power needed:

Motors draw between 3-5 times their operating power during startup. The

vsurge power needed to start a new motor then falls back to the operating

power of the appliance. This can be a vacuum cleaner, refrigerator, etc.

Let’s say you have a refrigerator that uses 500 watts and surges to 4x that

amount, or 2000 watts at startup. You already have 2500 watts of load in

operation when the refrigerator turns on.

Surge Load = 2500 watts of existing load

+ 2000 watts to start the refrigerator

Total
4500 watts of surge needed out of your generator.

Most generators have a continuous power rating and a surge power rating.

Use the surge power rating to determine if your generator can start the

newest load with other appliances running.

All generators also have a continuous load rating. Once the refrigerator

above has started, it needs 500 watts to run. Add this to the 2500 watt

existing load, and we have a new load value of 3000 watts. In order for the

refrigerator to continue working, the generator must put out at least 3000

watts. This should not be a problem in this case; surge capacity is rarely

more than 20% above continuous capacity, so a 4500 watt surge generator will

have at least 3500 watts of continuous power.

One last caveat. Generators above 2500 watts usually have a 220 Volt

output. This means that there will be two 110V legs, that are opposite each

other (see below for a more detailed explanation). Carefully balance the

load between the two 110V legs or else the circuit breaker on the overloaded

half will trip, even though the total power load is below the generator’s

capacity.

AC Power tutorial – AC, or alternating current, is a power source that

changes from going above zero volts (known as ground, or neutral) and below

zero, then back to above again. It goes positive, zero, negative, zero 60

times a second (or 50 times in Europe). The voltage on an AC line varies.

How do we get the voltage value then?

If a resistor is placed on a direct current, or DC, circuit, it generates a

certain amount of heat. The higher the voltage, the higher the amount of

heat. The amount of heat generated is equal to the voltage across the

resistor times the current through it. For AC power, the AC voltage is that

voltage level that will generate the exact same amount of heat (averaged out

over a second) as the same DC voltage would generate over the same length of

time. Because there are times in the AC cycle where the voltage is zero,

there will be other times where the instantaneous voltage actually exceeds

the listed value so that the average is the listed value.

Most houses have appliances that use 110VAC. In this arrangement, one lead

is the neutral, or zero volt lead, and the other has 110V on it. Some

higher power appliances (ranges, ovens, air conditioners, electric

resistance heat, clothes dryers, etc.) will use 220V so that they don’t need

as much current to get the needed power. In AC power, the voltage goes from

zero to positive, zero, negative, and back to zero again. If a second AC

power leg went from zero to negative, zero, positive, and zero again a the

same time, it would be opposite the first leg. A 220V appliance uses both

legs to get an average of 220V.

Generators above 2500 watts will generate 220V power, with two legs of 110V

each on opposite sides of neutral. Each leg will have a 20 Amp circuit

breaker on it. As mentioned above, balance the load so that each leg sees

approximately the same power. If too much load is carried on one leg, it

will exceed 20 A, trip the circuit breaker, and all power is lost.

The above mentioned refrigerator (as well as any other 110V appliance) can

be placed on either leg of the generator.