variable speed motors

[melt]

I want to switch out the motor on my blower to a variable speed one, anyone done this? With the winter coming and less fuming happening I want to tone down the airflow with a dimmer type switch & new motor. I currently have a 3/4 horse motor 110 volts. Any ideas of a good place to pick one up besides grainger or McMaster Carr. I don't want to pay full retail. thanks

[Big Jay]

With the winter coming

holy shit winter comes early in NH ? Why not just buy a Rheostat to adjust the fan speed? Or just use a dimmer switch?

[Mike_Aurelius]

Not a good idea.

Your current fan/motor combo is designed to put out a certain amount of air and using a variable speed defeats the purpose of the system.

Spend the money instead on ducting your fresh air supply into your workstation up under the bench through the bench top behind your torch.

[Primathon]

Lightbulbs work well with dimmer switches, but motors and the like don't play quite as nice. You'll likely get buzzing and probably a high-pitched whine, and your motor is probably going to heat up considerably more than if you were running it at full blast. This has to do with the way your motor is internally designed, the spacing of the electromagnetic coils, the spacing of the commutator strip and brush contacts, etc.

That said, you can DO it, and it'll more or less work, but it's not the greatest idea. Get your motor too hot and *poof* no more motor.

And that high-pitched whine may just drive you straight crazy.

[jplovell]

There are vairable speed motors in modern gas furnaces and air handlers, but their output is driven by brand-specific algorithms present in the furnace control board. I don't know if a used one could be easily reconfigured for your requirements, but they are out there.

If you hae a squirrel cage (centrifugal type) blower, you can reduce the output to a certain degree by altering the static pressure on the output side. This is done by either lengthening or constricting the duct. It would be a good idea to have a multi-meter on hand to ensure you are not drawing too many amps through the motor. A 1/2 H.P. motor shouldn't draw more than 4.5 to 5 amps when it's fighting back pressure.

Joe

[jiminyrootkit]

many furnace blowers have multiple speeds, basically multiple windings on the motor that you use by connecting the different contacts.
typically there will be a black wire that is the common wire, you hook up the common and ONE of the other wires to get the different speeds.
ideally you get a 5 position switch and put one winding to each contact on the switch and hardwire the common.
fyi, furnace blowers get pitched a lot because one winding (one speed) is burned out, so if it was a freebie, you'll prolly have one setting that squeals, heats up, etc.....i just clipped that wire off mine when i found it.
-f
ps. if you blow yourself up, i didn't tell you to do shit.

[phab]

...im using a $40.00 1100 cfm cheapie attic fan from lowes and i hooked it up to a dimmer switch. seems to work fine.

[Blacksheep]

also check out grow stores they have variable speed control units designed to work with fans that are better than a dimmer switch

[Lux]

I use a 3/4 hp 110V Dayton adjustable speed motor with a Penn belt driven inline centrifugal fan. I usually use it at full speed but if i'm using the lynx centerfire on my delta I will slow it down a bit. It is built differently than ac motors and can be slowed to a crawl without damaging the motor. It is almost identical to the Dayton motor on my Litton lathe. Grainger has them but they are not cheap (around $800).

Peace

[melt]

dimmer won't work, need a special motor and controller.

i don't mind matching the controller to the motor if the price is right. some controllers i've seen are pretty expensive though.

joe not a bad idea about constricting the output and it would work but i want to turn it down pretty low and the noise is more of a concern to me then the flow of air.

an attic fan won't do the trick with my hood & ductwork. i've already had lots of experience with those and they are ok for some places but i like my hood better.

seems like a five speed motor would be the most economical. its good to know that you can clip the wire to a particular winding to quiet it down some.

thanks for all the replies