[slowhand]

Those are pretty good examples. Let me try to simplify it more if I can.

You look at the welder's meters and you're running 150 amps @ 26 volts.

Multiply those numbers together - 150 x 26 = 3900

Since amps times the volts equals watts then you're welding with 3900 watts of electricity.

Now comes an interesting point. The efficiency of your machine. That means "how efficient it is at converting line power to welding power". A pretty crappy machine will have an efficiency rate of about 80%, where a more efficient machine will be closer to 94% or so. You should be able to find its efficiency rate in the owners manual.

For this simple example lets assume it has 90% efficiency rating at our 150 amps output.

So simply divide our 3900 watts by 9 then multiply that sum by 10.

3900 / 9 = 433.3 X 10 = 4,333 watts.

Thats your total draw at the amps and volts you're welding with plus the in-efficiency of your machine to convert the electricity.

And like said above, you can't weld 100% of the time so you now must guess at how much time you actually are welding during that hour period. Lets assume its about 50% of the time.

So 4,333 / 2 = 2,166 watts

Thats your load on the grid averaged out over the entire hour.

If you are paying the average $0.12 cents per 1000 watts of electricity based on an hour's worth of draw - then:

$0.12 x 2.166KW = $0.26 per hour

That should be pretty close, and pretty easy to figure.
Good luck