Nov 042013

When you do a web search for generator sizing, you will find plenty guides and online calculators. Most of them provide a list of typical wattages for common  appliances. Unfortunately, their numbers may be inaccurate even when they come from major manufacturers. To demonstrate this, let me consider as an example the power consumption of a refrigerator.

The chart below shows the values provided for a fridge in the sizing guides of some generator manufacturers (at the time we compiled this review on 11/2013):

Source Running watts Starting watts
Honda 132-192 (for Energy Star) 1200
Yamaha-motor 600 2800
Generac 500 1500
& Stratton
800 1600
Gillette 600 1950

As we can see, these numbers vary from 132 W to 800 W!
Measuring power consumption
Out of curiosity, I took Kill A WattTM meter P4400 and measured the consumption of my old Whirlpool model ET18DKXBN01 during various modes of operation. Here is what I got at medium cooling setting:

Mode of operation Current, amps Power, watts Volt-amps Power factor
Idle 0.36 32.6 43 0.75
When compressor operates 1.73 197 207 0.94
When defroster turns on 4.5 542 542 1.0

At initial power up the input current was 7.3A, which corresponds to more than 800VA. I realize the meter may not necessarily caught the starting peak current, which could be higher. By the way, I also measured the net energy consumption in a steady state operation over one hour- it turned out to be 0.13 kWh, which is 130W average rate. Of course, different models will produce different results. That’s why if you need to determine the required size of your genset don’t trust much any guide- just do the measurements by yourself.

Update: For a complete step-by-step sizing procedure see my home generator review and buying guide.