Electric Welding for Free???

[jack11]

I've been doing quite a lot of welding lately, but have not noticed any appreciable increase in my electric bill over what we normally pay. I wonder if it's because of the way the “smart” utility meter on my house measures energy (I don't know what's smart about it, in any case it's a meter just like all my neighbors have).

I use a Lincoln AC stick welder, which is basically a large iron-core transformer. On the grid side there is a primary winding connected across the 240V split-phase grid supply. On the weld electrode side there are secondary (high current ranges) and reactor (low current ranges) windings connected in series. I don't know how close to saturation this iron core operates, but I don't see any DC control winding that would bias the core and reduce the inductance.

So, to the grid and to the meter, this welder should look like a large inductive load (voltage leading current). The primary winding has some resistance of course, so this load is not 100% inductive. But, the PF may be close to zero when the welder operates, and the average power it takes from the grid should be small (P = V * I * PF).

The question is how the utility meter measures all this. I recall from another thread someone saying here that the meters do not bill for reactive power (energy cycling back and forth between grid and reactive load), and that no penalty for low PF is assessed in residential service.

Is it possible that a utility meter does not bill for the reactive part of the mostly-reactive power of a transformer-based welder – this would explain my low electric bill?
Has anyone observed this before while using his/her welder?

[DamonHD]

Usually domestic users are billed for real/actual power, with no penalty/extra for reactive power unlike significant commercial users, I believe.

Rgds

Damon

[joestue]

correct, the meter doesn't bill you for reactive consumption.

but that's not why you didn't notice a significant increase in consumption..
its because welding doesn't actually consume that much power.

I'm thinking around half a kilowatt hour per pound of welding rod.
edit: looks like .5 to 1 KWH/lb depending on the details.

[dbcollen]

Incorrect, look at your meter, the new smart meters measure VA. if you watch it scroll through the screens you will see it say "VA" I had a consult job at Guy Feirri's house to address why when he put 25kw of solar in his bill went up. the only other change was a new smart meter when the system was commissioned. the new meter reads VA and most of his large loads have a poor PF (air cond, pool pumps.... etc)

[birdhouse]

although welding does draw a lot of juice, it's pretty irregular.  i think it's pretty easy to overestimate the amount of time a bead is actually being laid. 

a company i work with does lots of public art sculptures in town.  they bought a brand new miller welder with an hour meter on it.  they never paid much attention to it until they had completed a whole bunch of steel sculptures.  they were astounded at how low the hour meter on the machine was with the size and number of sculptures produced! 

adam

[jack11]

Good points made about the welding power requirements, although I did quite a bit of heavy-duty welding with long duty cycles, and expected to see some impact on my electric bill.

I've looked closer at my utility meter, it measures energy in kWh and power in kW, so it looks like I get billed for the active power component only. There are some other markings on the meter: Va (not VA) and I, but I don't know what they relate to.

Also, reading about it some more I found out some government jurisdictions apparently prohibit the utilities from charging for reactive power. On the flip side, my service contract with electricity provider states that the provider has the right to disconnect the service for “interference with other users” or “use of non-standard equipment”. I wonder if low PF use would fall into any of these categories.

[joestue]

@Jack, only if your neighbours complained about brownouts, or if you blew up their transformer with a half wave inverter, would they ever find out.

yes, most regulations state that they can only charge you for active loads.. but they charge industry for both active and reactive, however, they also charge industry less than half the residential rate for the active load.