Slowing an AC induction Motor

[tubesornothing]

This might be similar to G Hoffman's thread, but a little twist.

I bought myself a used industrial sewing machine for making amp covers.  It is excellent, but holy crap it is fast.  Efiin scarey fast.  I can probably get a smaller drive pulley, but since I got a couple of variacs kicking around, I am curious - can I use a variac to control the speed with no ill effect?  It looks like a typical 1hp 1720RPM induction motor.

thanks
ToN

[jjasilli]

Checkout ths thread:  http://www.electro-tech-online.com/electronic-projects-design-ideas-reviews/10476-looking-ac-motor-speed-control-circuit.html

Also see: Inductive motors require a variable frequency control. http://www.aaroncake.net/Circuits/acmotcon.asp

http://www.fairchildsemi.com/an/AN/AN-7511.pdf

[tubesornothing]

Hey thanks.  Yeah I kinda thought it wouldn't just be a voltage adjustment.  I just re-read PRR's response to G Hoffman leslie motor control thread.  http://www.el34world.com/Forum/index.php?topic=7982.0  He basically says the same thing.  Since this is an industrial sewing machine, its not the typical universal motor.  Its same size as a 15A table saw motor.

I think I need to re-gear it (pulleys).  I just finished stitching up a couple of tarp zippers.  If I knew what I was doing, I could have done the 8 ft of zipper in about 30 seconds.  This thing rips.

[PRR]

"Sewing machines" traditionally use "Universal motors", NOT induction motors.

The no-load speed is another clue.

Does it have brushes? Does it spark?

> It looks like a typical 1hp 1720RPM induction motor.

Then maybe it IS an induction motor. But why 1 whole Horse for sewing? Why 1800 when 3600 is cheaper and it must have a belt anyway?

[tubesornothing]

This is not a home sewing machine - it is an industrial machine.  1hp motor - for sure induction (i.e. not universal - no brushes anywhere).  These babies are designed to run flat out, but there speed can be varied somewhat because it has a clutch (no kidding, a real live clutch).  I spoke with the local sewing shop (which also sells the industrial machines) they sold me a pulley for $10.  He did try to upsell me to a DC motor with speed ranges - but I did not want to fork out the $300

[billcreller]

I've used one of those industrial type machines. lots of power for heavy material. Don't remember if it was variable speed.