Question- Variable transformer and speed controller differences?

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)

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

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.

to

needed?

to

melt

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

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.