Generator rating

[Trainer]

How do I convert the watts to load. In other words, how can I take the watts, say 7000 watts, and determine what it will operate at my house. Is there a formula to help determine what a generator will do?

 

[slowrev]

All of the electrical devices in your home should have a label on them stating the electrical wattage. Add the wattages together of the appliances, etc that you want to run plus some for lights and see how much wattage output you need from a generator to run them. Note you will have to go higher than the total wattage because when electric motors start they require a lot more than normal wattage for a couple of seconds or so. There is probably a formula for how many extra watts to allow fopr starting surges. But I do not know it.
Do a search on this site for Generators, if you have a lot of reading time /forums/images/graemlins/smile.gif
Or do a search for Generac or some other brand of generators, I am sure some of the manufacturers have a lot of info on their web pages.

Ben

 

[Soundguy]

I think the watt rating is already a good unit for comparison.. if you needed amps.. divide watts by voltage... I.E. my roughly 12kw genny can pump out 50a at 240v etc..

All your appliances should probably have a wattage rating on their UL listing tag... add em up and see what you get... lamps are easy.. read the bulb rating... etc.

Units with motors are a special case.. depending on the age and design, for most, at least figure 2x wattage to start and 1x wattage to run. for older or other designs, figure 3x wattage to start, and 1x wattage to run.. I.e. if you havr 6kw of load on your genny, and want to start a motor/inductive load... if you are lucky.. you will get a 400-500w unit to start.. and quite possibly as low as 300w. mind you.. you may have some leeway with 'surge' capability and overall 'quality' ov your genny, and also it's engines ability to maintain speed ( frequency dependent), and lug thru heavy loads without dropping voltage or loosing freq tolerance. In other words.. I'd trust my 12kw genny hooked to my 90 hp tractor to lug thru a load vs a dedicated 12kw unit powered by a 24hp gas engine... etc. ( 2hp per kw is a good 'safe' figure for genny to hp rating.. etc. )

Soundguy

 

[kennyd]

Here is a good link that should help you out...
Wattage Calculator

 

[kenmac]

Is that 7000 surge watts ? or 7000 run watts ? You should b able to run alot of stuff that are on 110 v with a 7000 run gen.

 

[VA_Joe]

It can get even trickier. If the generator load is not balanced between the two 120v legs - you will not get the full capacity out of the generator (each leg provides half the rated watts). I would add an extra fudge factor onto of your calculated loads to make up for this. Soundguys 12KW unit has a lot of margin behind it for most residential power backup situations.

BTW - for the electric water heater and central AC - this is not a concern since they are 240v units and therefore pull both sides evenly. Its the window AC units and fridges that I would be most concerned about.

Joe