New (for me) blower control

[newbiesmith]

Thanks to keithh999 I have a new electric blower to replace the one that died on me last month. Thanks a ton man.

I figured that while I was at it I might as well look into "refining" the blower control mechanism that came with blower when I bought the forge. The old blower had a dimmer switch between the power lead to the blower and the wall plug. It worked great, yet my only complaint was that if I wanted to turn off the blower, I lost the speed setting it was at. To get around this I had marked the "sweet spot" on the face plate with a red sharpie. My current plan involves having a standard light switch in front of an analog (dimmer) switch so that I can cut power simply by flipping that one off.

The materials I have are as follows.
* 2 Feet 12/2 with ground
* 1 Standard Light switch
* 1 Analog Bar dimmer
* 1 Dual outlet wall box (gang box)
* Faceplate
* Blower with 2 Black leads going into it (thanks again keithh999)
* 1 ATX Computer Power Supply Cable (with the end that goes in the computer cut off).
* Electrical tape and wire nuts.

Attached is a roughed out design. So far I'm half way there and wanted to get some early feedback. Primarily because I'd prefer to minimize my chance of peeing sparks because of something I missed. Let me know what you think. If this is something that you guys think is helpful, after I validate it's operation first hand you can put it up as a blueprint ;-).

-Dan

[OldeScouter]

No, the wiring diagram looks all right. You might want to have all pieces of the wiring the same gauge. I see you have 12/2 for the switch wiring, but the ATX cpu cord is 16 gauge, rated for just 10 amps. It may heat up from all the juice you'd be pushing thru it. I would suggest you find a heavy duty extension cord or STO cord, with a 14 gauge/ 15 amp rating.
[ basic rule of thumb: 16 gauge=10 amps; 14 gauge=15 amps; 12 gauge= 20 amps. ]

I use that same setup on the garage and trailer forges. I just wired the dimmer into some 'scrap' yellow STO cord [14/3] from work [panel shop], which I use a Stinger shop vac for the air blast thru 1-1/4 inch pipe.

[JohnW]

So newbiesmith, what is an analog bar dimmer anyway? I have a common dimmer switch, the type intended for light fixtures, hooked to my vacuum cleaner blower, and it's not entirely suitable. There's a limit to how slow you can make the thing run before it stops. I guess that could be the motor, I can't identify the limiting factor. Anyway, I cut a slot in the pipe to the forge, so I can insert a plate to adjust the air, and I think I will use a plate to adjust the air intake for the vacuum cleaner.

I'm glad to see that you have a blower, and I hope that your motor, dimmer combination works better than mine.

A while back, somebody mentioned using a router speed control to control their blower. I'm sure it's better preforming piece of geer, and a little more expensive, of course.

[newbiesmith]

I guess when I say "analog" I am talking in computer terminology. Analog usually means non-binary would be the best way of describing it. A simple on/off switch consists of 2 states. An "analog" dimmer switch like I am referring too is a regular dimmer that has a series of states between off and full on. So your probably using what I am talking about.

What your running into is the same kind of issue that I ran into before with my old one switch system where the only switch in the circuit was the dimmer. The point at which there was not enough current to turn the squirrel cage in the blower and where it turned it the speed I wanted to was soo close that I hated having to turn the blower off. That's why I wanted to introduce a second on/off switch so that I could leave the analog switch set to the "sweet spot" and turn the blower off using the on/off switch when i didn't need the blower. That way I don't have to spend the time everytime I turn it off leaning over the blower to see at what point the cage starts spinning.

-Dan

[rlarkin]

Be carefull using a plain old "LIGHT DIMMER". Most are not designed for INDUCTIVE LOADS.
You can get ceiling fan speed controls that will work a lot better. They are designed for inductive loads.
Another good controller is a sewing machine pedal. I use one on my dremel.
And make sure you are not using a capacitor start motor.

[ThomasPowers]

Universal motors---the ones with replacable brushes on them can be slowed by cutting down the voltage so the *old* rheostat dimmers would work very well with them.

How ever a lot of the new dimmers work by chopping the wave form, which is great for a light or pure resistance load but very bad for motors that use the wave form to work.

So you have to know what type of motor you are using and what type of dimmer you have before hooking them up.

Also a lot of motors do better being started a full speed and then being turned down once they are running. Marking the sweet spot is a good idea.

All this is one reason that choking the air inlet is preferred by a lot of folks...

[Walking Dog]

Newbiesmith - There are two different types of motors that you are likely to encounter on your squirrel cage blower. One is the "universal motor" that Thomas mentioned; the other is a "shaded pole induction motor." The first is what you usually see on the very old forge blowers, and also in electric drills, vacuum cleaners, and hair dryers. Universal motors are identified by their brushes, and they generally respond well to the electronic speed controls. The second type of motor, shaded pole, is common in ceiling fans, phonograph motors, and most modern low-powered bathroom fans and the like. There are no brushes, but there are one or two heavy copper shorting bands wrapped around part of the stator iron in the motor. Speed control for these is more of a problem - as Thomas said, use a throttle in the air inlet.

It won't hurt to try an electronic speed control on the shaded pole motor, you'll get some limited results and if you're happy and the motor doesn't overheat, it's OK. Don't spend a lot of money on it, though.

As mentioned, the light dimmer may or may not work well on an inductive load. The electronic speed controls such as made for a drill or a Dremel tool may be better. Other choices are a "rheostat" (old sewing machine pedal), or a "Variac" (expensive, but they're around). These all function by reducing the effective voltage to the motor. The shaded pole motor really wants a voltage AND frequency adjustment to vary speed.