OT Electrical switch quesiton

[Greenfrog]

For lack of a better place to post this, I have a 3 speed furnace fan motor(squirrel cage fan) that I salvaged. It has three separate wires, hi, med, low, and the common coming off the motor. I want to rig this up to uses as a fan in the shop, just for circulation. I want to use all three speeds. What kind of a switch do I need? -- A single pole, triple throw????Can I even find such a thing? I can rig it up with three separate switches, hooking all the commons together. Question: however, what would happen if I "accidently " flipped two of the switches on at the SAME time?
Home Depot guy said to use a ceiling fan switch, but that does not accommodate all three wires. ??? Thanks for responding to this non tractor question!!!

 

[da.bees]

Most certainly damage will result if power is supplied to 2 sppeds at once.
You can but a 3 pole switch but I don't see why you need all 3 speeds.
Just use a double pole double throw ( dpdt ) center off toggle switch for hi and lo speeds. They are available at Home Depot or any place that sells electric supplies. Just make sure it has enough amp rating.

 

[CJinMI]

Most readily avail switch would be use 2 speeds, a spdt switch. Switches are out there, might have to dig a little. One speed at a time or the smoke gets let out. Block 1/2-2/3 of inlet or it"ll burn up, it will actually speed up and move more air restricted.

 

[slim51015]

You could use two spdt center off switches....
hot to common on sw 1
one side of sw 1 to low
other side of sw 1 to common on sw 2
one side of sw 2 med
other side of sw 2 to high

sw 1... up=low
center =off
down=power to sw2

sw 2...up =med
center=off
down=high

 

[Geo-TH,In]

Greenfrog,
I use rotary swithes that were used on old window air conditioners. Most were 3 speed. 20 years ago I worked on air conditioners. I have a box full of used swithes. They come in handy for many things, heavy switch.

Just wired up a 3/4 hp, 3 speed, 220 volt squirrel cage blower. Installed a 50 ft cord on it so I can use it any place. Put it on a 2 wheel cart to make it easy to move around. It moves some serious air. Great way to blow dirt out of the pole barn too.
George

 

[Greenfrog]

Explain the restriction of the air intake or the outtake. The heat/ac man said something about restricting the out flow...and said it would speed up. I don't completely understand the physics here...

 

[Greenfrog]

Yes I have already thought about the wheels, etc.

 

[Greenfrog]

You got me thinking.....thanks....all of you who have responded...

 

[Greenfrog]

I would like to use all three...just because they are there. Quiet on low, noisy, but moving a lot of air on high, and med. was just about tolerable....

yes, pertaining to the above post....I thought about rotary switches.

 

[john *.?-!.* cub owner]

(quoted from post at 22:08:28 03/31/13) I would like to use all three...just because they are there. Quiet on low, noisy, but moving a lot of air on high, and med. was just about tolerable....

yes, pertaining to the above post....I thought about rotary switches.

ot an AC man, but from experience, the motor cage assembly are designed to move a certain amount of air against a certain amount of restriction. The restriction is the heat exchanger, the A coil of the AC, the length of the ducts, and the size of the vents, etc. You can find the amount of restriction once you get it running by using a piece of plywood and sliding it down over the outlet opening. At a certain point you will notice the motor speed up. That is the pint where it uses the least current, and will last the longest.

 

[david - or]

You can do this with an ordinary household single pole switch feeding two ordinary household three way switches.

The first switch is the master on/off. The switched hot lead goes to common on the first three way switch. One side of the first three way goes to the fan high speed wire. The other side goes to common on the second three way. Medium and low come off the two sides of the second three-way switch.

If we think of power flowing from left to right we get the following truth table:

Sw1 Sw2 Sw3

D D D Off
D D U Off
D U D Off
D U U Off
U D D Low
U D U Med
U U D High
U U U High

With this arrangement you cannot accidently flip the switches to a bad position.

 

[PJH]

A burner switch from an electric stove (old style) has a pretty good amperage rating, and would give you the hi-med-lo positions that you need. I always salvage the burner switches when someone junks an old kitchen stove.

 

[david - or]

A centrifugal blower operates according to a fan curve. The lower the static pressure, the more air gets moved. The more air gets moved, the higher the power draw from the motor. The impeller and motor are designed to assume some static resistance to airflow (an A-coil and at least modest ductwork). If you try to run it as a stand-alone ventilation fan without any restrictions at all, it will overload the motor.

You need only rig up some sort of sliding damper in the flow path of the fan output. close down the output flow path until the motor speeds up (torque load reduced), and you will be at a safe power level.

 

[MarkB_MI]

Rheostats only work on DC (brush-type) motors.

 

[Jaden]

A choice of switch also requires one of correct amperage. How many amps does the motor nameplate show?

 

[PJH]

I"m so out of touch that I didn"t know they used rheostats on electric ranges.

I was referring to the multiple contact rotary burner switch found on older electric ranges.

Off-Hi-Med-Low

 

[CJinMI]

Restriction is also on the "return", besides its easier to let a piece of metal or something suck up to the inlet than try to keep it from blowing away. I AM a furnace 'guy', family since the 40's,
done it a hundred times, have a bunch here. Heard the same argument many times. Restriction = restriction. I knew someone would bring it up. I've even been told it doesn't matter.

 

[CJinMI]

Sorry, the post about resriction was towards david-or. To answer your ?? with out resriction the wheel gets to much air and overloads the motor. Take some air away and it will come up to speed and actually move more air, then the motor is running properly and also gets enough cooling air over it. Compare to overloading a truck or tractor and lugging it or reducing the load and letting it work properly.

 

[Bob]

If you GOOGLE SP3T switch, LOTS of choices come up. Here's ONE:
3 speed, NO off position