I bought:
A 250W fan speed control, for the fan.
A 1000W dimmer, for the smaller heating element.
A 2000W dimmer, for the larger heating element.
several wires, connectors, etc.

I'm gonna connect this stuff up asap; if no more cautions/advice is given here.

All sounds good. Those are big honking dimmers, but yes, an incandescent filament and a heating element are extremely similar, electrically.


Remember that you have a neutral wire; this is common between the fan motor and the heating elements.
You also have a hot (power) line, this is common between all the dimmers and speed controls.

If that doesn't make sense, draw it all out first.

I'd suggest adding a switch on the upstream side of all the dimmers, so you can set a position for all your controls and still conveniently turn everything off.

Given the way that I normally end up doing things, I'd probably also add a 3 way (SPDT) switch for the fan control, so I could switch between full speed and a preset low speed without twizzling the knob.

Not the best schematic I've ever drawn, but it should give you a rough idea. The normal switch would be main power - flip this switch, everything goes cold. The 3 way switch should flip between full speed fan and variable speed fan - potentially useful for going into a "cooldown" mode. Use the correct speed control/dimmer for the correct load, and it should all be OK.



Your math is close - on 29 ohms @ 120v, I get 4.1amps, just under 500 watts.

i=e/r (amps=volts/ohms), watts = volts * amps.
(I'm overlooking power factor, because these heating elements can be considered a purely resistive load.)

I AM NOT AN ENGINEER. YOU ARE DOING THIS AT YOUR OWN RISK. I accept no liability for any incidents resulting from the use of any of this purely speculative information provided for entertainment purposes only.

Great, William, thanks for the schematic and everything else!

Is accidentally switching neutral & hot a Bad Thing in this setup?

Probably need to check how that thermal switch operates if you're going to use it. If it's an open on rise, it should read about 0 ohms when cold. Ideally, you can point a heat gun at it while measuring the resistance (clip leads are your friends here) - hear a little "tink" noise, and see the resistance shoot up to open circuit. If you have a thermocouple handy, you can figure out what temperature it's going to do that at.

If that's the case, wiring it into the circuit with the heaters should be OK. Don't wire it into the circuit with the fan - if it over heats, letting the fan continue to run so that the heat goes away is probably a good idea.

I just did a little math on your dimmers - if you haven't opened the 2000W dimmer yet, you might want to exchange it for a 1000W if there is an appreciable cost savings. 16ohms@120V=900W - well within the 1000W dimmer capacity. The 2000W will certainly work, and the heatsink on it should stay cooler than a 1000W dimmer.

coffee.me wrote:Is accidentally switching neutral & hot a Bad Thing in this setup?

Yes and no.

Electrically, it shouldn't matter. Safety says you switch the hot leads.

Always unplug it before moving wires around.

Never work on energized equipment - you're a self proclaimed non-electrical type.

coffee.me wrote:I have no electrical/electronics background.

Go slowly, plan your work, work your plan. Don't get excited; don't rush. Mistakes happen when you try to skip steps or go too fast.
The most important piece of safety equipment is a few inches behind the eyes, just between the ears. Use it.

Thanks for answering the polarity question and for the tips.

Espin wrote:If it's an open on rise, it should read about 0 ohms when cold.

I think it does. When cold, it reads 0.5ohm, but that's also what it says when I make the MM leads touch. I checked where it connects to, and it appears it's online for one of the leads of the larger heating element. So probably no probs leaving it as is.

My IR2 is now fully upgraded to stick shift . . . I think I can get to C2 in 3mins .

As a curiosity, does it seem to work OK with both heaters on full and the fan on full?

What's your intake/exhaust temperatures on full speed fan with heater a, heater b, and both once a stable condition has been reached?

It's an intriguing project.

Yup, all seems OK. I ended up wiring the two heaters together and controlling them thru the 2000W dimmer; it was alot easier to do this way because of how the IR2 heaters were originally wired.

I did a few browns last night and the thing is hot. I got some Brazil (75g) batches to FC(+) in 7mins and one Sumatra to a rolling C2 in 7mins. I didn't log temps, but I recall seeing 600F on the MET TC. I suspect MET can get to 700F in 1 or 2min if required. Do you want me to verify?

Just wondering how hot it can get at full fan speed, and what your ambient is to get up to that temperature.