multiple speed furnace blower

Greetings,     Just got a new furnace for the house. ouch. Snagged the squirrel cage fan from the old unit. (Eyed the burners, but let them go.) This fan has five
electric connections; one for common and four to select the fan speed. Heat used one speed, A/C used another.
    Checked out the Google archives for this group. I don't trust the dimmer switch idea for this fan. A bank of light switches on the yet-to-be-built case could select fan speed. The deadman switch idea is one I hadn't considered, but will add one to the common when I do the case.
    My question: Any body here played with this sort of fan? I want to know if I'd fry it if two of the speed circuits were live at the same time. The 120V rotary switches I've found on the web seem all to be make-before-break.
--
"Keep your ass behind you"
wreck20051219 at spambob.net
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On Thu, 11 May 2006 15:37:54 GMT, Australopithecus scobis

I wouldn't switch the common. That leaves everything at high voltage. Check the NEC.
Pete Keillor
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On Thu, 11 May 2006 11:42:51 -0400, Pete Keillor opined:

Oops. Thanks for the heads-up.
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Pete Keillor wrote:

<I wouldn't switch the common. That leaves everything at high voltage.>
Wouldn't this be ok if the common to the switch (before the motor input leads) were the hot leg? Seems like a better idea than having the return hot because then the rest of the circuit will be effectively dead when the switch is turned off. I think this is what you meant to say; guess it depends on your definition of common.
Actually, now that I think of it what's a deadman switch used for in this circuit; just testing?
dennis in nca
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Hi All, If the "fan" you are describing is what I think it is, from an oilburner? You should know that these fans put out relatively high volume but low pressure air. They will not work very well for a coal forge as they provide a feeble blast. You need air pressure in a coal forge. You need a blower not a fan. A $20. 6" blower from Graingers will do it.
In general, a better way to control blast with an electric blower is to use a simple butterfly valve in the air line situated near your hand so you remember to use it.
Burned a few, Glen G. Pgh.
Australopithecus scobis wrote:

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It's not little like this one, right?
http://www.panix.com/~alvinj/burner.htm
I'm picturing a big blower like the one in my furnace that also has four speeds and the motor is inside the squirrel cage.
I've pulled a few of little-blowers out of furnaces at the scrap yard (and abandoned ones out in the desert) only one so far was ~120V instead of the usual 240V. YMMV, don't know nuthin about your electric service there.

Oh man, the light dimmer idea sucks for these types of motors.
Sloppy as hell. :/
The baffle idea works like a champ, instant, precise changes can be had with a baffle. If the motor is inside the squirrel cage blower then the air will need to come into that side and go over the motor, otherwise the motor (like in the one pictured) will see a much lower "load" with the air cut off.
I've been using that one all the way closed since I reduced the burners to 1/2" bushings. Almost all the air it gets comes through the motor.

I see lots of arcing on the switch points in your future? ;) (but don't know for sure). :/
I say, forget the various speeds and first try the baffle idea. :)
Alvin in AZ ps-
http://www.panix.com/~alvinj/drills.jpg
Now that's what a light dimmer is good for... single speed, double reduction ~1000rpm power-drills... works great! :) pps- yeah, I have a Milwaukee VSR and it's nice but not as good for pocket knife work as either of those two drills with the light dimmer, IME ppps- ceiling fan speed controllers are the same thing except they come on full blast and slow down as you "twist it" farther, also they have a speed adjustment which I needed to change on the two I have for drill use
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On Thu, 11 May 2006 19:21:07 +0000 (UTC), snipped-for-privacy@XX.com wrote:

I had a 2 speed motor on my furnace blower for about 12 years, running with the low speed live all the time, and the high speed kicked in by the furnace control.Had no problems at all. Just put in a new medium efficiency, 2 stage burner, with variable speed DC fan to replace the 30 year old unit. It didn't save me $20 per year on gas, but the power consumption has dropped to less than half.
***
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Australopithecus scobis wrote:

My bet is that the motor is an induction type with multiple windings to control speed. The more windings energized, the higher the magnetic field strength and the higher the final speed against the fixed aerodynamic load of the squirrel cage. "Dimmers" don't work on induction motors. Lock it in high and use a positive airflow control valve on the output, like a butterfly or sliding door. That way you get the most effeciency from the motor. If you want a kill switch, use a double pole switch and kill both lines at once; can't go wromg that way.
Charly (one wire at a time, Mr Sparky has a really strong grip when you shake hands with him)
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Australopithecus scobis wrote:

I have one of these blowers that I used for a shop fan. Each one of the wires represents a separate speed. I salvaged a multiple position switch from an oven, figured out the connections with a continuity checker and hooked it up to the blower. Now I have a 4 speed fan. I believe you can only hook up one speed circuit at a time. That's the way the wiring diagram showed it to be used. This is a 220volt blower, so it has to have it's own special outlet, can't be used just anywhere. Like someone else said, it doesn't produce enough pressure for a forge or melting furnace. I believe that these blowers need to run with some restriction over the output.
The blowers from downdraft ranges can be used for forges, not quite the pressure you'd like but OK.
--
Gary Brady
Austin, TX
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This is a 120V squirrel cage. The output will be restricted at the tuyere, if not by the plumbing upstream. I can't believe that a fan which will blow air through an entire house can't feed a forge. I wonder if, indeed, this fan might push too much air through at the high speed, blowing heat away inefficiently.
Wondered about running a Y up the chimney. If there are enough cfm coming out of the fan (haven't located the specs yet) the tuyere could get what it needs, and the excess could drive a draft up the stack.
It looks like life will be simpler if I just pick one speed and adjust flow with a butterfly.
Thanks for the tips, all.
--
"Keep your ass behind you."

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