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Question- Variable transformer and speed controller differences?

Discussion in 'Misc Electronics' started by ME, Apr 13, 2005.

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  1. ME

    ME Guest

    Can someone tell me what the differences are for:

    120-volt, 15-amp variable transformer - (about 150.00)
    120-volt, 15 amp ac motor (router) speed control -( about 20.00)
    and are they interchangeable

    I will be using it as a temperature control for some nichrome wire to melt
    and bend plastic.

    or anything else cheaper to use for this.


  2. A triac and a trigger circuit. Total cost: >5$.
    A triac turns on the current when it's triggered by a short pulse, and
    turns it off again once the phase is 0, i.e there is no voltage present.
    Over a purely resitive load, this works great, is dead cheap, can handle
    _huge_ loads (10's of kilowatts can be triggered with a few mA for a mS
    or so)
  3. Jim Gregory

    Jim Gregory Guest

    Speed control triac can only be used with a "brush" AC motor as it needs to
    go through 0V every cycle.
    What is the max current through the resistance wire at hottest temp needed?
    [I guess it's possibly worth your trying an incandescent lighting Dimmer
    module (usually covers up to 300W, about 2.8A in USA).
    Be aware! some cheapo, sub-standard dimmers do not reduce voltage/current to
    "very low" as effectively as the better-made ones.]
  4. ME

    ME Guest

    Thanks for the help Jim
    but from what I have figured out so far I need to run approx 10.5amps
    through 11 Ohms (115v) to get the
    temp I need to melt the plastic. (1200 watts)

    Actually I am working on making a homemade Vacuum forming machine. Have
    everything figured out except the heating part ( need about a 12" square
    heater) and working with Nichrome is not as easy as it sounds, but don't
    want to fork out big bucks for a ready made heater, so thought I would make
    my own.

    Looks like I have some more reading to do.

  5. Zak

    Zak Guest

    A 'light dimmer' should do what you want.

    However take care that the whole heater is connected to mains. Don't get

    Using a (surplus) transformer of decent wattage could work too. Depends
    a bit on the voltage of the secondary, if it gives you any choice. You
    can get a lower voltage; maybe this helps you constructing the heater.

    To reduce the power of this you need a dimmer for uinductive loads.
    These are more expensive. OTOH if the transformer has multiple
    secondaries, use those to adjust the power.

  6. Jim Gregory

    Jim Gregory Guest

    The low-value resistance is at cold/room temperature. Surely the Ohms will
    rise appreciably when it warms up to optimum temp.
    I am not familiar with Nichrome thermo-electric law properties, but the
    cold-surge current will drop inversely very promptly, so hot Wattage will
    become a figure smaller than you calculated.

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