How do I slow down an electric motor?

[TheOldRedneck]

Call one of your local electric motor shops and give them the info that is on the motor data plate. Some motors will not work with speed controls. Also if you are looking at a fractional horse power motor buying the right motor will be cheaper in the long run. As you drop motor speed on some a/c motors you also drop horse power. D/C and brush type motors work better as a group when you vary voltage. A/C motors that use variable freq drives are wound for them. It is possible to slow a regular motor but cheaper to change pulleys, doubt you will get right combination, or just get the right motor.
As a side note some of the China made wood and metal lathes and tools use some weird wound motors that have bolt patterns for the mounts that are not like our regular motors. Their rating system on horse power also does not always match ours. Have had to build adaptor plates and play with different motors to get some to work. Down here you find these motors cheap at flea markets, and junk places sometimes. They are not a good deal unless you can make money on them for scrap. Stay with something like Craftsman put on it when they built it.

[rodfair]

DONT DO IT! Change the sheaves/pulleys, but you said it was direct drive. A motor designed to run at a certain speed is just that. The fan at the end of the motor will not cool it adequately.
Buy a new motor from Grainger or someplace like that...Probably cheaper to buy a new sander.

[Sarge]

You need a pulley twice the size of the current one to slow it down roughly in half.

Sarge

[GunsandNoses]

A drive pulley twice the size of the driven pulley would cut your RPM in half or 1725, close enough to 1700.

[gbusmech]

Yup, Change the sheaves/pulleys to slow it down or risk burning up the motor. You may be able to reverse/switch the position of the sheaves from drive to driven too....

[IDLE]

Yes I would not alter the motor voltage with these devices this is a motor rated for one speed not variable speeds as this could and mostlikely will cause worse problems. Your 2 best options are
1. Imcrease drive pully size x2
2. Buy or trade for a new/used motor to match desired RPM

[TrucksNCoffee]

Thank you all for the information and advice. The posts about pulleys jogged my memory, so I went to the garage, rummaged in the Dark Places, and found a Champion mount with an all-in-one, five different sizes small to large cast pulley installed on the shaft. Perfect! I'll buy a length of 2X10 and a v-belt and perform some do-it-yourself assembly. I appreciate all of you.

[bre346]

There is such a thing that is a variable transformer. Plugged into that can give you a wide range of control. But a half-horse motor is gonna call for a big controller. Dbeardslee has good info.

[Aberdog1]

Theres gotta be a joke in here somewhere.... Maybe only plug it in half way. I'm not and electrician..

[CDinNM]

Glad you found the step-down pulley, they are the best choice, you can buy them at most all lumber companies and hardware stores. You only other alternative would be to use a VARIAC, they are designed specifically for motors. You can search your actual motor on the net and get it's specs, in the specs will be information about drop down power use, tells you what the lowest speed is. Most motors have ratings on them for their max speeds, but all motors also have specs for lowest speed as well. Some motors have TAPS in the windings, you can move your TAP connection to a different TAP to also achieve different speeds. Getting specs on a motor is always a good idea, and usually you get more info that you are seeking, like the tap info.

When I buy equipment, I always look up everything I can find on things like motors, print it out, keep a file of this extra info with manuals, etc. And if you don't have a manual for something, you can find them on the net too. When I buy a gun, I look up the manual on the net and save it as a pdf, that way if I ever loose my manual or dont want to bother with getting it out, I can just click on the pdf.




CD