Router Speed Control to Adjust Temperature

Just starting a brew session with a new (more watts) heating element and something crossed my mind that a quick search didn't help.

If I throttle back the wattage on an element with a router speed control will the amperage draw on the line before the speed control be less also? Or is it the same and the difference is being absorbed (turned to heat) by the controller?

I'm curious about how it effects the chances of the circuit breaker tripping and if that chance is less when I'm running at a lower level of heat.

All depends on how the router speed control regulates the router's speed. Also, depending on the wattage rating of the controller you might get a "poof" and a room full of smoke.

It's a Rockler speed control that's rated at 20 amps. The element is 1650 watts. It's only drawing about 14 amps at the 115 volts the power company's feeding me today. It's on a 20 amp breaker. My concern is that there is other stuff on the same line, so I was hoping that turning the Rockler down would be lowering the amps drawn on the circuit.

If it works like other controllers I've looked at and designed it will reduce the average current draw but not the peak current draw. You could look at it as a switch that's turning rapidly on & off. This would have a impact on other things on the same power that rely on clean power, like a PC or anything that draws a lot of start-up current like the compressor motor in your fridge. Lights won't care, neither will any motors that are already running.

When doing some testing last week I put an amp probe at the element connection. I did this to figure what the wattage of the element would be at different settings on the variable speed control. But isolating a wire before the speed control would have been a PITA. Suppose I could do it at the panel in the basement, but was hoping someone could save me that hassle.

When under a load, do router speed controls like my Rockler draw the same full load amperage regardless of the setting?

I have a plug and receptacle wired together with individual conductors so I can check amperage on plug-in appliances. It's quick to make and may be useful elsewhere too.

I would not know otherwise.

lschiavo said:

It's quick to make and may be useful elsewhere too.

Click to expand...

hmm . . . nice idea!

Probably take less time to make than running up and back from the basement.
(. . . but think of the beer calories I'm burning. )

The Rockler speed controllers will get a little hot during use...I remember reading a thread on another forum advising adding a heatsink to the the back plate of the controller FWIW???

Mine gets a little warm, but not hot. That's what made me suspect that it was raising the amperage drawn.

Not getting hot could be because I have mine piggybacked with a Johnson 419, so it doesn't have power going to it constantly.

The router speed controllers are usually a Phase Angle style of controller, and they DO reduce amperage draw. The heat you feel is not from a resistor, it's the switching circuitry. Like any electronic circuit, heat is developed when it changes state (ON/OFF).

You can use it no problem, and you'll have the benefit of lower current draw when it's dialed down.

Phase angle control is not like the PWM stuff, PWM is usually switched at slower rates with the circuit design being used here. The phase angle stuff actually switches at line cycle speed 60Hz, and only allows the circuit to be on for a selected portion of the cycle.

swede, interesting stuff. Thanks!

I got an email from the Rockler tech guy. He didn't know too much, but dug up that it's a silicon controlled rectifier (SCR). Did some google searching, but much of it is over my head. Anyone got the layman's version of how this applies to controlling a heating element?

A SCR is a thyristor. It only allows current to flow when voltage is applied to the gate. Some SSR use SCR's if this makes any sense. Pretty much its a "relay" with no moving parts that switches very fast to control a cycle. Same concept as using a SSR.