resolved - a wiring question answered, easy for the right guy

Ronin42 · 2018-06-16T00:55:58.000Z

As I don’t have an online photo program, I may not be able to post a drawing (sorry).

Ok hear’s the deal, I have a working old, old 120VAC heater/fan.

Super simple:
Wire goes from wall to switch #1 (Switch #1) is for the fan.
Then a wire goes from switch #1 to Switch #2 (switch #2 is the heater coil, very old school)

So the heater can only turn on when the fan is switch on.

Here my question:

The fan runs too fast (too much noise, air output too cool) what I want to do is to have the heater coil (coil runs right from switch no “electronics” in this beast) turn on first and have the fan run slower or not at all (depending switch position).

Aside from reversing the orientation of function and switch, what should I be adding to the fan portion of the circuit to slow the fan down but leave plenty of power to go to the coil remember resistance is fixed (do to length and diameter of coil wire).

Thank you in advance.

gadabout · 2018-06-16T01:04:55.000Z

Not to be a downer but unless there is some kind of overtemp safety cutoff, slowing down the fan sounds like a real fire risk.
Some kind of rheostat in the fan wiring would probably do what you need but I’d look for a thermal cutoff first.

Ronin42 · 2018-06-16T01:46:36.000Z

I hear ya.

But this is an old Cast Iron beast. I have other coil heaters without fans. Perfectly silent and heat up the nearby space well enough.

If I find it’s running hot (remember its all steel and iron there is nothing to burn) I can A turn the heater off, or B Turn the fan on. What I really want to do is just have the fan run nice and slow, like in the background a gentle warm “Zephyr” was the Greek god of the west wind, which was considered the gentlest wind.

moderator007 · 2018-06-16T01:52:05.000Z

You could buy one of these and wire it directly from source to the fan, it has its own switch. Run the heater straight from the source wiring in the existing heater switch. Basically two separate circuits with a speed controlled fan and a heater both switchable. Either one can run without the other or both at the same time.
You could also wire in something similar to this for saftey. http://www.galco.com/buy/NTE-Electronics/NTE-DTO250
Model depends on where you want the on and off temp and current. Find one you like and add it to the heater circuit.

Ronin42 · 2018-06-16T01:55:43.000Z

Looks interesting.

I guess I was looking for something simpler. It does not need to be necessarily adjustable.

I was guessing, something like wiring in a resistor in line with the fan. Which I think is sort of the same thing just hard wired as opposed to plugged in. Maybe the router controller can run two lines one full on and the other controlled. Not looking to turn the heater down.

Heck if it comes to it I might be able to run smaller wires to the fan so it can draw less juice?

moderator007 · 2018-06-16T02:24:32.000Z

Both the heater and the fan need to be wired parallel from the source coming in to the device. So each has its own power separate from the other.
Didn’t know if you understood that part. The way its wired from your description in the first post is in series. Putting a resistor in a series circuit would slow both devices down.

Lightbringer · 2018-06-16T02:56:12.000Z

Not to be Mr Glass Half Empty but it’s not really trivial.

Chances are the fan’s driven by an induction motor. They don’t take too well to being current-limited, and even a relatively small decrease in voltage/current can slow them to only a small fraction of their usual running speed under load. It might not even start up at all.

Also, as the fan ages, and the bearings get “stickier”, you want to start it up full-speed and then ramp it down to a lower speed, else it might not even start up at all. The fan in the vent-hood over my stove is like that, that starting it on low, it’ll sloooowly spin maybe 1-2rpm (not kidding) unless you start it on high to get it moving, then switch to half-speed.

I got a heater, too, where the fan just lost its oomf, and if it gets turned on and doesn’t immediately start spinning, the heater coils will glow a nice bright orange (high R9 value, even), and then the thermal breaker trips. Not fun, or safe.

Last, the coils need a certain minimum breeze to not immediately burn up. Turn off or block the fan, and you’ll see. Same principle as a hotwire anemometer. If you slow down the fan, and it’s not meant to take that, the coils can overheat and burn up. So I wouldn’t even try to slow the fan to half-speed, but no more than 20% or so, if I had to hazard a guess.

Soooooo, that might be the only reasonable way to do it, ie, partially block the fan from the back, where it draws air in. Even some filter paper or something. Better yet, tie a string to it so that in case you see the heater going supercritical, you can just yank it off and let a full breeze cool it down.

Phlogiston · 2018-06-16T04:39:09.000Z

My advice is: buy a new heater. Skip the potential for safety-critical mistakes and having your insurer refuse to cover the consequences.

Having said that, I did notice this:

Ronin42:

Heck if it comes to it I might be able to run smaller wires to the fan so it can draw less juice?

Don’t do that. The wires will get hot. In the worst case scenario, they’re liable to melt, and then you have a probable short circuit and a fire hazard.

Lightbringer · 2018-06-16T05:43:07.000Z

Phlogiston:

My advice is: buy a new heater. Skip the potential for safety-critical mistakes and having your insurer refuse to cover the consequences.

Yep. Stereo bursts into flames, insco adjuster sifts through the rubble, finds that the fuse in the stereo isn’t UL rated, denies the claim.

Real or urban legend, dunno, as I don’t have firsthand knowledge of it, but some adjusters can be pretty hard-ass.

Yeah, I wouldn’t wanna hacque up a heater (notorious enough for causing fires), let alone give someone a legit reason to DQ a claim.

Ronin42 · 2018-06-20T19:04:27.000Z

All good advice, thank you.

DavidEF · 2018-06-20T20:01:25.000Z

Trivia Fact: Fixed resistance heating elements will work on lower voltage, but will put out less heat, commensurate with the voltage.

Putting a resistor in-line with the fan motor won’t help. AC electric motors rotate according to the phase frequency of the alternating line voltage. Because of that, you need a PWM speed control. You can actually buy a ceiling fan speed control wall switch from Lowe’s and have a three-speed fan. But, that would have to be wired into a switch box somewhere. Or, you could buy that device that moderator007 linked from Harbor Freight Tools and use that. Either way, the heating element needs to be connected directly to the electrical source, and the fan needs a PWM speed control, to do what you want to do. Since the unit is heavy metal (you said Cast Iron) it shouldn’t be a fire-hazard, but you should definitely start it in high at first, to confirm it is wired correctly, then turn it down to medium, and check to see if all is well, then down to low and see if all is still well. Don’t leave the heater un-attended unless there is literally no flammable material nearby.

Ronin42 · 2018-06-23T22:35:24.000Z

DavidEF

Now that is excellent information.

I may look into putting a less efficient fan on.

Thanks every one

Lightbringer · 2018-06-23T23:26:50.000Z

Or, you could just put a piece of paper-towel over a quarter of the intake vents, maybe a half if it needs a bit more restriction, etc.

Why cut open the beastie?

DavidEF · 2018-06-25T19:51:45.000Z

Lightbringer:

Or, you could just put a piece of paper-towel over a quarter of the intake vents, maybe a half if it needs a bit more restriction, etc.

Why cut open the beastie?

He wants not only less air flow, but also less noise. He said it is too loud at full speed, and thinks it will be quieter if he can slow it down.

millerman · 2018-06-25T21:15:01.000Z

umm replace the fan with a quieter one ?

Lightbringer · 2018-06-25T21:26:58.000Z

DavidEF:

He wants not only less air flow, but also less noise. He said it is too loud at full speed, and thinks it will be quieter if he can slow it down.

I got one of those big white square freestanding fans, and when it’s a little too close to the door, not only does airflow suffer but it’s hardly audible. I actually need the “noise” to drownd out outside noises.

It still has a few ft³ behind it, but it’s not “free” air.

Personally, I’d rather try it the cheap way to see if that works, before resorting to open-hearth surgery.