Router Control for 220V

[AnOldUR]

Just had a thought (dangerous, I know) and haven't researched it yet. Thought the electric pros here might have a quick answer.

I'm using a 26 amp router speed control to adjust the output of a 120V element for my MLT. Works fine. Could one of these be used on one leg of a 220V element to adjust the output in the 50% to 100% range for controlling the intensity of a boil?

 

[SweetSounds]

That depends entirely on what your speed control is rated for, and how it's actually limiting the speed of your router.

There are essentially 2 ways to control speed.
One is by lowering the delivered voltage to the device. In other words, turning the dial from 100% to 50% reduces the delivered voltage to the device to 60 VAC.
The other is PWM, which ALWAYS delivers full 120 VAC to the device, but switches it on and off really fast, based on a duty cycle. If the duty cycle is 2 seconds, for instance, and you set for 50% power, it's 100% ON for 1 second, and 100% OFF for 1 second. Most PWM circuits are much faster than 2 seconds, however. More like 20 times per second.

Here's where it gets interesting though, and I think you don't understand 240 volt circuits.
A 120 volt AC circuit has 2 wires - 120 volts, at up to the rated current, flows in one and out the other, switching directions 60 times per second.
A 240 volt AC circuit has 2 wires - 240 volts, at up to the rated current, flows in one and out the other, switching directions 60 times per second.

Notice that these are identical, except for the apparent voltage potential between the wires. This means that by applying your speed control to one wire of a 240 volt circuit, you don't get 50% to 100% control - There is NO 120 VOLT wire in a 240 volt circuit
You are throttling a 240 volt circuit from 0% to 100%

Essentially, if your router speed control is wired inline with only one of the wires in the 120 volt circuit (Which I wager it is), you could wire it inline with one wire of your 240 volt circuit, with the same results.
HOWEVER! Current capacity (ampacity) and voltage ratings change between 120 and 240 volts. It's imperative that you determine that your router controller is rated for the new load and voltage.

For instance:
A 120 volt 2500 watt element pulls 20.8 Amps
A 240 volt 2500 watt element pulls 10.4 amps
But, even if your router control is rated for the current, if it's not rated for the voltage, you're gonna let the smoke out - Or worse...

 

[AnOldUR]

My convoluted thought process went something like this. I’m guessing that the neutral leg and the ground pass through the router control, and the voltage is lowered on the hot leg. What I thought could be done was to run one 120V leg directly to the 240V element and pass the other 120V leg through the hot side of the controller.

I have no idea how this would affect the phasing or if it’s even possible. Just brainstorming out loud until someone shoots the idea down. I don’t even have the need to do this. Just wondered if it would work?

 

[SweetSounds]

There is no 120 volt leg in a 240 volt circuit. Both wires are 240 volts. Both wires are 120 volts in a 120 volt circuit.
Hot and neutral are irrelevant in a single circuit.

 

[AnOldUR]

I was thinking it would be something like running two 120V elements in series on a 240V line except that the router control would offer additional resistence on one side lowering the wattage of a 240V element in this case.

 

[SweetSounds]

The resistance of one element is fixed. It doesn't matter how you wire it. Study up on series and parallel circuits and it'll make a little more sense. If you add additional resistance - lets say 2000 watts - in series with a 2000 watt 240 volt element, you'll present a load of 4000 watts to the circuit.

The big question is what is the make and model of your control? Then we'll know what the ratings are. If its PWM and rated for 240 you're golden. If its something else, you're probably screwed.

And at the end of the day, you could just get a $40 PID and $5 SSR and get there anyway.