pushing luck

Discussion in 'General Electronics Chat' started by PackratKing, Mar 10, 2014.

  1. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    How far voltage-wise, can the primary of a huge transformer - Pic 1 - be pushed...

    Is it possible, to push a normal primary of 120 vac, to say.. 150 volts, to squeeze more output voltage from a heavy-guage - #8 - secondary...as in pic 2

    I have more than one of these, and wondering if it is possible to cascade them, playing games with different lead combinations, without creating a lot of scrap copper...
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Normally, to minimize size and cost, power transformers are designed for little more than their maximum rated voltage. Above that the core can start saturating and the magnetizing can become dangerously large. I think 150V would likely be too much for a 120V rated transfomer.

    If you have a variac, you can vary the voltage while monitoring the transformer primary current. The current will exhibit a sharp increase when the core starts to saturate.

    To protect the transformer when testing with different voltages you can put a incandescent bulb in series with the primary. When the voltage is too high, the magnetizing current will cause the bulb to be significantly brighter. Pick a bulb wattage that, at the transformer rated voltage, causes the bulb to be dim or dark.
     
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  3. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    Information very much appreciated !! I had done a half-baked search in other locations, none had this advice...
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Frequency and current are limiting factors more than voltage. The only key issue with voltage will be the insulation breakdown.

    The benefit if 240 vAC in parts of the world is that transformers can be smaller because current demand for a similar wattage appliance is smaller. Wire diameters can be smaller for a given wattage circuit (1800 = 120 volts x 15 amps). You will only need to carry 7.5 amps for a similar load on 240 VAC lands.

    In other words, monitor the amps, the voltage wouldn't be my biggest concern (until you get to insulation breakdown levels of voltage).
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Not true. Voltage is as important as frequency. If the voltage goes much over, or the frequency much below the rated, the core can saturate and the magnetizing current rapidly increase to damaging levels. Insulation resistance normally has little to do with the maximum primary voltage that can be applied.
     
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