Convert 240V motor to 120V?

[TheChief]

Picked up an HVAC blower/motor from someone on CL with the intention of building a downdraft table. At the time they stated it ran on 120V but I was in a hurry so didn't check. So, of course, when I finally get around to testing it, it's a 208-240V motor (sigh).

So... scoured the net to see a motor designed for 240V could be converted to run on 120V. Couldn't find anything specific. Failing to find something clear my pea brain can digest, I ask you folks: is it possible to rewire a 240V motor to run at near capacity on 120V?

Here's what I know or think I know:

Current motor has this for wiring:

White: 240V Leg 1
Black: 240V Leg 2 (for High speed)
Blue: 240V Leg 2 (for Medium speed)
Red: 240V Leg 2 (for Low speed)
Yellow & Yellow/Black: Reversing wires (these are connected)
Orange & Orange/White: Reversing wires (these are connected)
Brown & Brown/White: To starting capacitor

From what I understand a typical convertible motor has four wires... call 'em 1, 2, 3 and 4 (creative, ain't it?). For 120V operation 1 & 3 would be connected to 120V Hot, and 2 & 4 connected to 120V Neutral. For 240V operation, 2 & 3 would be connected to each other and one leg of 240V would go to 1 and the other to 4.

Problem is that I cannot figure out whether or if the convertible wiring applies to the motor I have. My lizard brain says surely, with all those wires sticking out there must be a way to do this...

For what it's worth, I don't mind opening up the motor itself if necessary to make this happen. I'm a fairly handy electronics tech, just not very familiar with motors.

Thanks for any info, guys!

[Tom Slick]

nope, a 208-240V motor is 3 phase is wound completely different than a 1 phase motor. A 3ph motor will start spinning on its own, a 1ph motor needs extra parts to get moving.

post the data from the plate on the motor.

[jackellis]

If you can't rewire this motor, get another furnace blower at any heating contractor's shop by removing it from a replaced unit. I got two for the time it took me to free them from old furnaces that were headed to the scrapyard.

[LCHIEN]

my take is that you have a single phase 240V motor (because it has a start capacitor) with multispeed capability.
That probably precludes being wired for 120.

I'm not real familiar with multispeed motors.

[bruce hylton]

I just replaced the motor on my hood fan at the restaurant. It was a two speed motor, 1140 or 1725 rpm, 120 volt or 208-240 single phase. This was built by GE as an OEM motor and would have cost me almost $300 plus shipping and a week down time. Therefore I replaced it with a single speed motor and had to change the wiring from 208-240 to 120 volt. There was a schematic on the plate over the lead in wires that told which wires to switch. I do not remember how it came about, but by following the directions, we got it to work.

[Tom Slick]

good catch Loring. I read right past the "Brown & Brown/White: To starting capacitor" it may be able to run on 120v.
Usually 208-240v motors are 3ph.

[master53yoda]

possible to rewire a 240V motor to run at near capacity on 120V?

Here's what I know or think I know:

Current motor has this for wiring:

White: 240V Leg 1
Black: 240V Leg 2 (for High speed)
Blue: 240V Leg 2 (for Medium speed)
Red: 240V Leg 2 (for Low speed)
Yellow & Yellow/Black: Reversing wires (these are connected)
Orange & Orange/White: Reversing wires (these are connected)
Brown & Brown/White: To starting capacitor

this motor came out of an electric furnace and is not convertible to 120 vac.

sorry about this not good info fort you, could wire it for 240, did you also get the blower.

[master53yoda]

you said that you are and electronics tech, a motor is simply a transformer with a shorted secondary winding( the rotor) and the shorted secondary is free to float in front of the wave form on the rotor bearings.

The motor windings (acting as the Primary) are wound very similar to a transformer with varous voltage connections ie You must insulate all the unused speeds.. for example if you connected 240 to the L1 and low speed you would get close to 300 VAC (RMS) from the L1 to the high speed winding. just like you would on the different power taps on an electeronics transfomrer.

Just food for thought.

[TheChief]

I'd like to thank everyone for their input! It just doesn't look like converting this particular motor to 120V will be feasible. If it were a single-speed motor, maybe. Hopefully with a little wipe-down and a good description I can sell it on CL and not lose anything on it.

Thanks for the suggestions of hitting up a local HVAC contractor. Will look into that and see what pops up.

In the mean time, won't be getting my downdraft table but did take advantage of Woodcraft's Jet sale to pick up an AFS-1000B. Might even get the company to pay for part of it since I'll be building at least six custom cabinets for mounting/testing various home control/automation interfaces for the QA Lab that will involve a lot of MDF cutting and routing. It'll be another week or two before I get to see how well it works to keep the dust down but it seems like it moves enough air to help.

Anyway... thanks again, everyone!

[Tom Slick]

Grainger sells a lot of HVAC components like motors.