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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

    Hello,
    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.


    Thanks

    Ron
     
  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

    ME
    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.]
    Jim
     
  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
    'shocked'...

    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.


    Thomas
     
  6. Jim Gregory

    Jim Gregory Guest

    ME
    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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