Slowing a table saw down 240 - 110V?

Sambostar

I'm thinking about temporarily converting a 10" table saw blade to a disc sander, angle grinder, glue, velcro, sandpaper sort of thing, but probably need to slow the revs down a touch.  Could I just wire it to my site 240/110V transformer and use that to reduce the voltage and maybe buy a 13A 240V female to 16A 110V plug adaptor?

It would be handy as I don't need a sander all the time, just for bodies and furniture feet and stuff, where as I need a table saw.

Is my 110V site equipment AC still?

ICBM

Yes, the 110V is still AC - it's just stepped down, not rectified.

I think it should work, although I've never tried it. Not sure how much speed reduction you'll get when the motor isn't under much load though.

I'm pretty sure you have the option of 55V as well - the 110V is centre-tapped to earth, in order to keep the potential shock hazard as low as possible. (110V by itself is still considered hazardous.)

I doubt you'll be able to buy the adaptor you need since it has no legitimate use, but it's easy enough to make one.

Sambostar

You can actually buy the adaptors, don't know why, but yeah, it'd be cheaper to make one.

BigMonka

I wouldn't be surprised if it was torque you lost rather than speed actually.

Mkjackary

doofus comment 

ecc83

If it is a brush motor it is likely "series wound" and therefore AC/DC. The speed of a series wound motor is infinite unloaded!

In practice of course there is usually some load, if only a cooling fan*. Reducing the input volts will reduce on load speed as others have said because there will be less current driven through the motor.

If it is a single phase induction motor of the sort you find on a small drill press up to 1/2 a horse, the speed is related to mains frequency off load but again will reduce if voltage and hence current is limited.

*DON'T try this at home kids! But, if you strip out an old vacuum cleaner motor and take off the fan, put it in a bench vice and power it up it will scream and attempt Warp Ten and probably destroy itself!.....Oh! The things we did 50+years ago! Wonder I lived through it all.

Dave.

Mkjackary

If it is ac then speed is proportional to the frequency of the PSU. Which is about 50hz usually, I'd have thought changing current/voltage will only affect the power/torque as said above. If you could *somehow* lower the frequency at which the current alternates then I think that would lower your speed.

 

If you could find somehting that could vary the frequency then you could control the speed. No Idea if something like that is readily avaliable to an average jo however.

Sambostar

Ah. So frequency of the AC is key.  Hmmm...bollocks. Well in honesty, even less torque would be better as the thing wouldn't be so ferocious.

Then there are these:

http://www.ebay.co.uk/bhp/ac-motor-speed-controller

But I don't know what they do? Seem like voltage regulators to me.

blobb

You need to control the motor speed with a Variable Speed Drive (VSD). For an ac motor this can be a variable frequency drive (VFD). Sorry I don't know how you would go about getting one for a 'domestic' motor. I design sewage works and we use VSD motor drives a lot but 'tis what you might call 'industrial' use. The motor sped controller you link to could well be a VFD.

https://en.wikipedia.org/wiki/Adjustable-speed_drive

https://en.wikipedia.org/wiki/Variable-frequency_drive