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  1. #1
    Join Date
    Dec 2011
    Posts
    388

    Default Is PFC desirable or even useful in a non-commercial/non- industrial setting?

    Given that there is usually no penalty with regard to power factor in a residential setting, is it desirable to have PFC? I know that my local utility will love me for correcting power factor but not enough to give me a discount for doing so. I find that often in a project at home my welding machine may spend more time simply ON than it does actually welding. With the higher current draw at idle with PFC would I be better without it or with some form of automatic switching to engage it only during welding cycles?
    I think that Willie B(please correct me if that is not what you meant) is suggesting that this extra current, about 20 amps, may not be registering on my meter but I can't imagine my utility letting me get away with that. On the other hand at nearly 25 amps idle current on 230v I don't think I would see 5750 watts of wasted heat in my welding machine which I would expect to see if the machine was actually dissipating this current. Does anyone know if the standard residential utility meter is recording the real power or the apparent power consumed?
    There is of course the lighter requirement for wiring to consider with PFC. I fairly recently acquired a used Idealarc 250 without PFC(wrong color for this forum) but they are similar to the Dialarc and the question would apply equally to either. I am running this machine from a 40 amp breaker and although I have not done a lot of work with it, it has yet to trip the breaker even though the breaker is way too small for this size of machine. My concern is that if I was to add PFC that the in-rush current would be more likely rather than less likely to cause nuisance trips.---Meltedmetal

  2. #2
    Join Date
    Sep 2005
    Location
    northern NJ
    Posts
    1,840

    Default

    I do not think PFC is useful in a residential setting. I don't think it's useful in an industrial setting either unless you have a whole bank of welders going at once. I can't see how your meter would read "apparent" power. It reads what power is used, period. Having said that I don't think it would hurt to have PFC in a residential place because most people only run the welder as needed for a project so the extra current used at idle would be minimal.

    Many people run a Syncro 250 on a 50 amp breaker without issues. Not ideal but it is done especially in residential use.

    If I had a choice between two equally priced machines one with PFC & one without I would choose the one without.
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  3. #3
    Join Date
    Dec 2011
    Posts
    388

    Default

    MMW
    I think you are right about the economics of PFC in the residential setting. At $0.10/ kwh 25 amps figures out at something like $.60 per hour and really that's negligible in a home setting. In the commercial setting though the utility reads both real and apparent power to derive the power factor and penalize you accordingly if it is less that 90% (here at least). Our largest current draw is usually our melting furnace which actively compensates to keep the power factor close to 100%. But business has been slow over the winter and we got penalized because we also run some larger motors that are not always under load and our power factor slipped below the 90% threshold.
    Up until the advent of "smart meters",(I don't know how many functions they are capable of) the old residential meters must be reading either real or apparent but I don't know which although as you imply, from an economic standpoint it probably is not very important.
    I had read a thread on Welding Web in which the author had installed an automatic switchable PFC in a welder and I thought it might be useful to limit the working current draw(read smaller gauge wire) as well as benefit from the lower idle state current draw. Subsequent reading on power factor has now lead me to believe that it would be cheaper and less complex to just install a larger gauge circuit. It seems that constant switching in and out of of the circuit may introduce harmonics into the power grid which I could, though not likely, be required to filter out.
    Add to all that the PFC capacitors are, for my purposes, just another component to age and ultimately fail. Like you, I have come to the conclusion that in my circumstances if the welder I have does not begin to give me nuisance trips I will not likely change anything and if it does my first line of attack will be heavier wiring and breaker.
    Thanks for your reply.---Meltedmetal

  4. #4
    Join Date
    Dec 2013
    Location
    At the epicenter of the Green Mountain Range in VT
    Posts
    275

    Default

    Quote Originally Posted by Meltedmetal View Post
    Given that there is usually no penalty with regard to power factor in a residential setting, is it desirable to have PFC? I know that my local utility will love me for correcting power factor but not enough to give me a discount for doing so. I find that often in a project at home my welding machine may spend more time simply ON than it does actually welding. With the higher current draw at idle with PFC would I be better without it or with some form of automatic switching to engage it only during welding cycles?
    I think that Willie B(please correct me if that is not what you meant) is suggesting that this extra current, about 20 amps, may not be registering on my meter but I can't imagine my utility letting me get away with that. On the other hand at nearly 25 amps idle current on 230v I don't think I would see 5750 watts of wasted heat in my welding machine which I would expect to see if the machine was actually dissipating this current. Does anyone know if the standard residential utility meter is recording the real power or the apparent power consumed?
    There is of course the lighter requirement for wiring to consider with PFC. I fairly recently acquired a used Idealarc 250 without PFC(wrong color for this forum) but they are similar to the Dialarc and the question would apply equally to either. I am running this machine from a 40 amp breaker and although I have not done a lot of work with it, it has yet to trip the breaker even though the breaker is way too small for this size of machine. My concern is that if I was to add PFC that the in-rush current would be more likely rather than less likely to cause nuisance trips.---Meltedmetal
    I don't have a power factor corrected machine to experiment with. What I do know is: The pellet mill has a capacitor bank. 12 modules each supplied by 3 200 amp fuses can be connected simultaneously. That's up to 2,000,000 watts of heavy cable under load. Powering this monster, is four runs of three cables 500 MCM ( a conductor is about 1" diameter copper, there are 12 of them). Fuses blow often. Yet the net consumption of this hog is near zero! because it improves power quality, motors use less power to do their job, the net result is the electric meter records less usage. Motors start with greater torque, allowing them to lower peak usage, the demand rate is reduced. The power company rewards them with no penalty as our power factor isn't screwing up their grid. Aside from no penalty charge for bad power factor, there is the benefit of less power used. Power flows in but back out, perpetual motion, like a pendulum, an equal and opposite reaction. A pendulum expends energy on the upswing, but stores it on the downswing. The expended energy is limited to air resistance, and friction in the pivot. A giant tower clock runs a month on the energy a clock winder offers cranking the weight up to the top.

  5. #5
    Join Date
    Dec 2013
    Location
    At the epicenter of the Green Mountain Range in VT
    Posts
    275

    Default

    Quote Originally Posted by Meltedmetal View Post
    MMW
    I think you are right about the economics of PFC in the residential setting. At $0.10/ kwh 25 amps figures out at something like $.60 per hour and really that's negligible in a home setting. In the commercial setting though the utility reads both real and apparent power to derive the power factor and penalize you accordingly if it is less that 90% (here at least). Our largest current draw is usually our melting furnace which actively compensates to keep the power factor close to 100%. But business has been slow over the winter and we got penalized because we also run some larger motors that are not always under load and our power factor slipped below the 90% threshold.
    Up until the advent of "smart meters",(I don't know how many functions they are capable of) the old residential meters must be reading either real or apparent but I don't know which although as you imply, from an economic standpoint it probably is not very important.
    I had read a thread on Welding Web in which the author had installed an automatic switchable PFC in a welder and I thought it might be useful to limit the working current draw(read smaller gauge wire) as well as benefit from the lower idle state current draw. Subsequent reading on power factor has now lead me to believe that it would be cheaper and less complex to just install a larger gauge circuit. It seems that constant switching in and out of of the circuit may introduce harmonics into the power grid which I could, though not likely, be required to filter out.
    Add to all that the PFC capacitors are, for my purposes, just another component to age and ultimately fail. Like you, I have come to the conclusion that in my circumstances if the welder I have does not begin to give me nuisance trips I will not likely change anything and if it does my first line of attack will be heavier wiring and breaker.
    Thanks for your reply.---Meltedmetal
    It is important that at full load you are using 14 amps less than without PFC. Should you switch it off when not needed? I don't know.

  6. #6
    Join Date
    Dec 2011
    Posts
    388

    Default

    Thanks for the info Willie. That's a monster connection at the pellet mill. I suspect, but do not know, that I am paying for the unused watts that the PFC would eliminate during welding. My reality at home is that most of the time at home I will not be welding more than a couple of hours per week on average so the cost to convert to PFC is probably not an economically sound expenditure. Also I seldom weld most things above 150 amps so that would reduce the differential even further. I thought about a switchable set of caps like Kald did with his or something similar but I question whether switching in the caps every time I strike an arc would be an advantage or a disadvantage. I'm not sure either but if I ever think I've come up with a definitive answer I will test out the theory on the rest of the people here.Thanks---Meltedmetal

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