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doesn't this look suspiciously just like an elctric motor?I can't get this at all!

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  • PStechPaul
    replied
    Maybe it's a ploy to encourage replacement of incandescent lamps with CFLs and LEDs. You can just use a dimmer for the lamps to bring the effective voltage back to 220 for increased life, and the convenience of adjusting brightness (and color temperature) to whatever works well. But don't use a dimmer on CFLs or LEDs unless they are rated for that purpose.

    Another thing you can do is connect a buck/boost transformer to the AC mains. There are purpose-built transformers for this with buck/boost windings of 12, 16, 24, and 32 volts. For 100 amp 240V service, you can use a 2 kVA 24V control transformer which will have an output rated at 83 amps.

    Here is a 2 kVA 16/32V buck/boost for $275:


    It would drop the 252 volts to 236 volts at 125A or to 220 volts at 62A.

    And here is a 3 kVA 12/24 buck/boost for $250:

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  • awemawson
    replied
    Many of our light bulbs are made on 'mainland' Europe where the voltage norms are nearer 220v and hence the life of the bulbs on our 240 -250 is lousy - and they call it 'harmonisation'

    Andrew

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  • PStechPaul
    replied
    Having a higher voltage usually results in better efficiency because less current is needed for a given amount of power. This applies to most motors and anything with switching power supplies, and it also holds true for resistance heating devices, since they provide the energy needed at a lower duty cycle. It may not be good for incandescent lamps, however, since their life will be shortened, although they will emit more light at a higher color temperature. The increasing use of CFLs and LED lamps eliminate this problem.

    According to my father, many years ago the power company would replace, at no cost, any lamp bulb that burned out. That seems generous, but then again the customer will use and pay for more electricity if all their lamps are operational and being used.

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  • awemawson
    replied
    And that 'nominal 230V' can be as high as 252v here at times. We're first drop off the transformer. 11kV overhead comes to a twin pole mounted quite large transformer in our vegetable patch, and the 415v coming out goes first to my workshop, and then onwards down the road to a small industrial estate so we always see the highest on the line. The house takes phase one a couple of poles further along.

    Andrew

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  • Timleech
    replied
    Originally posted by J Tiers View Post



    I think you may find that your mains have been "harmonized" with the continent, to be a nominal 230V, instead of 240V. In practice, that may simply be a label.....voltages actually not changed.... with UK running on the high side of the tolerance, and the continent running on the low side, since your stated voltage tolerance is preferred at 5%.
    That's pretty much how it is. We're officially on 230V in the UK, but most of us are actually on 240V and will usually refer to it as that.

    I suppose a side benefit for the power companies may be that they can drop the voltage further & be within tolerance if we have severe weather & consequent system overload.

    Tim

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  • A.K. Boomer
    replied
    Hosie what's in the water over there? is it safe? if you put fish in it do they go belly up right away?

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  • J Tiers
    replied
    Originally posted by Alistair Hosie View Post
    are you sure the rope pull or idler starting slave motor works here in the uk I could see it might be easier doing this with 110v.Alistair
    We don't use 120V, we use the 240V mains for the RPC. That produces 240V 3 phase, with the 240V from line-to-line.

    In any case, rope pull start (which I do NOT recommend, by the way) simply gets the "idler" motor (the converter) started. After that it can accelerate to full speed if there is no load on it. Voltage or wiring makes no difference to that.

    Your 240V is line-to-neutral, and your 3 phase is 400/415V line-to-line. For a 240V line-to-line, you'd do what we do. To get 400/415V line-to-line, you'd need to do something slightly different, since the tapped winding method per above would get you 480V line-to-line, which is what we use.
    Last edited by J Tiers; 12-08-2013, 02:50 PM.

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  • The Artful Bodger
    replied
    The step up scheme using one leg as an auto transformer has the disadvantage that just one sixth of the machine has to handle all the power going in to it and considering the inevitable poor efficiency it might require something like a 10HP 3 phase motor to run even a very small lathe.

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  • Alistair Hosie
    replied
    are you sure the rope pull or idler starting slave motor works here in the uk I could see it might be easier doing this with 110v.Alistair

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  • J Tiers
    replied
    Originally posted by PStechPaul View Post
    If the 240 VAC is applied to a phase-neutral winding, the phase-to-phase voltage will be 240*sqrt(3) = 415 VAC. But normally the single phase is connected across two phases, with a capacitor to shift the phase to the third leg. If this RPC was purpose-built, it could have a special winding pattern that could boost the voltage. It may also be a 230/460 dual voltage motor, and you could apply external single phase voltage to the center taps and get double the output voltage, but at a much reduced power.
    The capacitor you mention is NOT NEEDED except for starting. The thing will produce 3 phase output without the capacitor.

    Many people use a plain 3 phase motor, either rope-starting it, or using a smaller motor to bring it up to speed. The motor is spun up by some means (rope, other motor, etc) to a reasonable speed, and then will accelerate to normal speed and produce output as normal.

    Some people DO use a capacitor arrangement to correct the power factor on the "generated leg" which will bring up the voltage (usually known as a "balance" capacitor). It cancels some of the motor impedance.

    The step-up should theoretically work, although it may depending on exactly how the motor is wound. The efficiency may be less than with a normal 1:1 voltage type. I have never done a step-up type. I may try it to see how well it works sometime.

    Originally posted by Peter. View Post
    UK mains voltages are very simple:

    Domestic: 240V single phase (live & neutral, separate earth)
    Industrial: 415V 3-phase (3 lives, one neutral, separate earth)

    All at 50hz
    I think you may find that your mains have been "harmonized" with the continent, to be a nominal 230V, instead of 240V. In practice, that may simply be a label.....voltages actually not changed.... with UK running on the high side of the tolerance, and the continent running on the low side, since your stated voltage tolerance is preferred at 5%.
    Last edited by J Tiers; 12-08-2013, 11:31 AM.

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  • Alistair Hosie
    replied
    I couldn't see the capacitors at all so thanks guys. Alistair

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  • Peter.
    replied
    Originally posted by The Artful Bodger View Post
    Bear in mind that this machine is advertised for sale in the UK where supply voltages and practices may not be the same as elsewhere.
    UK mains voltages are very simple:

    Domestic: 240V single phase (live & neutral, separate earth)
    Industrial: 415V 3-phase (3 lives, one neutral, separate earth)

    All at 50hz

    Leave a comment:


  • PStechPaul
    replied
    Since most of Europe (and possibly also Australia) use 50 Hz, equipment is typically rated at 50/60 of its US voltage, so 480 at 60 Hz would be 400 VAC at 50 Hz. AFAIK, the standard European voltage is 220 VAC line-neutral, which would be 381V phase-phase. The actual voltage can vary about 5%, so 380-420 would be within specification. With common use of VFDs and wide-input switching power supplies, the line voltage and frequency of the mains is not as critical as it once was.

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  • The Artful Bodger
    replied
    Bear in mind that this machine is advertised for sale in the UK where supply voltages and practices may not be the same as elsewhere.

    Leave a comment:


  • PStechPaul
    replied
    That is true in theory, but most motors are wye connected for 480 or 240 phase-to-phase, which is 277 or 138 volts phase-to-neutral. So, if you put 240 volts on the center tap (half leg), it will be overvoltage and probably saturate and draw lots of current at 60 Hz. However, it could be connected across two center taps, which would be OK. The 415V as claimed would most likely be the result of the sqrt(3) phase voltage relationship.

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