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Old 11-10-13, 11:39 AM   #1
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Default Eco mod my welder

I picked up a craftsman 230 amp AC welder for $100. It was in rough shape.
One thing I do not like about its rated for a .77 power factor.

This means that it draws around 11,000 Volt Amps of reactive or apparent power for this highly reactive inductive load. That is 50 amps of 220.
It draws 8.6kw of true power.

If the power factor was corrected to closer to 1 it would only draw 39 amps.

I figure if a few high voltage non polarized capacitors can knock 11 amps (of 220!) off the reactive load. How can I not do this?

Aside from saving 11 amps of utility power I would like to be able to run this off grid on a generator and I don't want to screw up the power for any other items being run off the generator. Also saving 11 amps of 220 when you are on a generator is very valuable.

Only problem is I am having trouble with the math that you use to figure out how much capacitor you need to correct power factor.

I think it will take 3 or four 100uf motor run capacitors to fully correct the P.F. when running the welder at full power. Or more I really don't know for sure.

Only thing I can think of is run it through my kill-a-watt meter, up to 20 amps and check the P.F. with and with out capacitors and then wing it with an amp clamp only from there on. If I get the power factor corrected it should read closer to 40 amps, if not then closer to 50 amps.

Then once I get this power factor thing straightened out I am going to convert it to DC.

The difference between an 0.8 power factor and a power factor of 1 means the engine has to work up to 27% harder to drive the generator.
On a generator you may not have the horsepower to do that.


Last edited by oil pan 4; 05-17-16 at 10:38 PM..
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Old 11-10-13, 02:38 PM   #2
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oilpan,

The main problem with passive (capacitor) PFC is that the capacitors will continue to draw current when you are not actually welding. Sure, you might use 10 amps less peak current, but you will be continuously drawing more than that 10 amps at idle. Instead of inductive reactance at full load, you will be drawing capacitive reactance at part load and idle.

The other problem is that power factor is a moving target. Depending on how many amps and how much inductance (dig or sharpness control) you are using, the power factor will change. The phase angle will change due to amp draw, arc length, material thickness, grounding method, cable length, etc. ON ITS OWN.

Another thing to consider is that capacitor "padding" the input of the welder only corrects for linear (or passive sinusoidal) mismatching. Anything active in nature (generators, regulators, rectifiers, transistors, etc.) pushed or pulled through causes harmonics, which could interfere with other parts of the system. One bad situation is feedback with the generator due to resonance.

Not trying to put you off your idea, but this is the kind of stuff that electrical engineers have fun with. Of course, they use sophisticated, expensive equipment, and even more sophisticated formulas and methods of figuring out what's actually happening in the circuit. Cuz with AC power, most standard test equipment lies to a certain extent.

Last edited by jeff5may; 11-10-13 at 02:39 PM.. Reason: grammar
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Old 11-11-13, 12:40 AM   #3
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It looks like I will be trying to find a happy medium then.
I think to cancel out that apparent power with the welder going at full power would take 480uf but all that unused reactance would be a waste. I don't plan on running full power very often.
I ran my machine some today and I think I will be keeping it between 120 and 180 amps for now 145amps seems like the happy place.

I could always run the capacitors on switches to cut way down on unused reactance.
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Old 11-14-13, 01:41 PM   #4
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I got the 100uf motor run capacitor I ordered in and promptly ran a quick test. I plugged it into my kill a watt meter.
The kill a watt meter detected 0 amps, 0 watts going to the capacitor, which is exactly what I was expecting.
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Old 03-04-14, 07:54 AM   #5
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What you are saying about reducing the load on a generator may be correct ?

But , I would like to point out to you , the reactive amperage is not read by the traditinal power company mechanical watt meter . Which is one reason PF is kind of a touchy subject with the power company . Not so much for residental , but for commercial or industrial companies .

I do not know if electronic watt meters can read reactive amps ?

I worked at an iron foundry , years ago . Two electrical induction furnaces . ( Big inductive reactance ! )

They each had a capacitor bank . The controls would switch in / switch out more or less capacitors . It would maintain a PF of from .95 to 1.05 .

Lastly , as long as you are hooked up to commercial power , it is probably a non issue , as long as you are not doing much welding . If you are doing a lot of welding , maybe so ?

God bless
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Old 03-17-14, 10:20 AM   #6
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I don't know what you plan to do with this welder but a 1/8" 7018, or 5/32 6011 rod will probably run comfortably at 110 amps or less. Your arc voltage will probably vary between 20 and 30 volts. 30 x 110 = 3300 watts when welding. You will You guys will have to do the math to account for losses while you backtrack to the 240v line. Your biggest amp draw will be when your rod sticks to the work.
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Old 03-21-14, 07:46 PM   #7
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Well it turns out the power meter can read apparent power.
Since I belive in math and reproduceable scientific experiments (unlike the AGW community), I will tell you what I did and how I did it. I dont make crap up and tell you to believe it.
You will need a power company power meter, kill-a-watt meter, 200w incandescent light bulb with drop light, and a 110v arc welder with a really horrible power factor.
I have a 2 main panels, since I split the lines coming out of the power meter. I turned off the house power so the meter was stopped. This leaves only my small power panel energized. No chance something can kick on and screw with my test.
Test 1, plug in the incandescent and count the number of seconds between marks passing on the disk.
It took 3 seconds for each mark to pass and check its actual consumption on the kill-a-watt meter.
Test 2 used my small arc welder with its horrible 0.22 power factor. It draws 120 watts of real power and 500 some units of apparent power. I removed the drop light and plugged in my welding machine in to the same kill-a-watt meter.
When the welder was flipped on it turned the power meter disk much faster. It was between 1 and 2 seconds per meter count.

Now if power meters only read true power then the welding machine with its 120watts of true power should have turned the power meter much slower than the 200w bulb with its 207 watts of measured true power.
Wouldn't you think?

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Old 03-21-14, 08:36 PM   #8
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To adress "power factor is always a moving target in a welding machine", umm its not.
Basically the excessive reactive power is a fixed amount. Then when you strike an arc true power and apperant power increase in unison, raising the power factor from say 0.22 or 0.33 to 0.6 or 0.7 at full load while welding depending on the machine. There is still roughly 400 more volt amps than watts, at no load versus full load but the ratio of watts versus volt amps is a lot better when under load.
The machines draws the same power factor reguardless of the output amps setting at no load.

I power factor corrected my mig welding machine with great results. I figured I needed at least 30uf of capacitance to get my machine into greater than 0.9 power factor territory.
So in installed a terminal board and put 30uf of 200v metalized film capactors in parallel with the welding transformer. At no load it brings my mig welders power factor from 0.33 to 0.55, while welding it increased the power factor from 0.7 to 0.92. I have some 2.2uf 200v metalized film caps in the mail, I am going to fine tune the pf up to .96 at full power.
And best of all its putting out 10 to 15 more amps than ever before, its drawing more true power and apparent power compared to before with the same settings as before and putting out more welding amps. Thats so not not a problem for a little 110v mig, I just turn down power or move faster.

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Old 04-10-14, 03:34 PM   #9
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Looking at a newstyle digital power meter there appears to be 2 power consumption measurements.
One reading appears to be tracking high power factor consumption when VAs are 20% higher than watts and the other reading appears to be billing just regular wattage.

I am sure power consumption at less than 0.80pf comes with a nice penalty. I would like to live in the same town where everyone has this meter.

So the mig welding machine is running well above 0.80pf, up to .95, but I have 2 problem air compressors, one runs a .7pf after some minor power factor correction (I added a salvaged 8uf oil filled motor run capcitor) and i have another compressor that runs a .44pf.
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Old 04-24-14, 10:34 AM   #10
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Adding 200uf of motor run capacitors to my main compressor has reduced apparent power consumption by 400 VoltAmps.
The pay off for this mod is 200 hours of run time, if there is no low power factor penalty on the digital utility meter.

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