Simple transformer Question

Discussion in 'The Projects Forum' started by zorpholex, Dec 11, 2012.

  1. zorpholex

    Thread Starter New Member

    Dec 11, 2012
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    I would like to have less current through a heating element.

    Now i have 120 volts across it. It is about 400 Watts I believe

    The simplest way to drop the current(AC CURRENT) would be a transformer correct?

    How much does a transformer cost that would drop it from 120v to say like 60 volts. And where do i buy it?

    Also, is this a reasonable way of going about this? or Is there something I'm missing?
     
  2. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    You can buy a 500 watt light dimmer for less than $20. A 400 watt transformer will cost a lot more.

    You want half power? Put a rectifier in series with the heater. Problem: cold start current. Probably have to use a 30 amp rectifier. Still way cheaper than a 400 watt transformer.
     
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  3. zorpholex

    Thread Starter New Member

    Dec 11, 2012
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    Yeah i think i want about half power, im not really sure exactly how much i need.
    Okay thanks i'l rule out the transformer possibliity then for such high power.

    A light dimmer would work for such high current?

    So youre saying that converting the voltage to DC would drop it in half? I dont understand how the rectifier will work.
     
  4. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    A single rectifier diode won't convert to DC. It will just block half the AC. Presto! Half voltage.

    500 watt light dimmers are actually expecting a cold start current. (They are designed to work with light bulbs.)

    ps, I should have said 200 watt transformer. Still not cheap. Try looking up 120V to 60V, 200 watts.
     
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  5. Audioguru

    New Member

    Dec 20, 2007
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    If you cut the voltage to half then the current also gets cut to half.
    Since Power= Voltage times Current then the power is reduced to one quarter.
     
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  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    People not qualified should not play around with mains equipment. And particularly NOT heating elements. The best solution to your problem is to get an approved 500 watt light dimmer. And then play with the settings
     
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  7. zorpholex

    Thread Starter New Member

    Dec 11, 2012
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    Okay yeah that makes sense the diode seems like the simplest method.
    Why does it matter if the light dimmer expects a cold start?
    I dont enve know what "cold start" means.

    THanks for the replies BTW
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Strictly speaking yes it will produce a DC voltage. But to be 100% correct. The output will be a pulsating DC voltage. Light dimmers are designed to work with restive loads. And a heating element is pretty much that. So a dimmer should work fine here
     
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  9. wayneh

    Expert

    Sep 9, 2010
    12,090
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    The resistance of a light bulb filament is temperature-dependent and increases as it gets hotter. That's why they don't go poof like a flashbulb - they self-limit current. But they draw much more current at the instant they are turned on and still cold.
     
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  10. zorpholex

    Thread Starter New Member

    Dec 11, 2012
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    Okay thanks, i understand it will be like a half wave rectifications so kinda like a sine wave with out the negative.

    I will try the light dimmer idea, that will be nice for fine tuning the correct temperature.
     
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