# AC Motor RPM



## Brad Green (Jul 29, 2004)

I wanted to pose a question for our Electronics Gurus. I know that you can vary the rpm on DC motors by voltage reduction, but can the same thing be accomplished on AC motors? I would like to reduce the rpm's on my Dayton motor FCG rig and I'm not sure how to go about it. Figured if anyone would know, they'd be here!


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## bradbaum (Jul 26, 2008)

not easily - it is very complicated to speed control ac motors.

DC motors are much easier to control and therefore are used in most small electronics, AC motors are used primarily in large industrial machines that speed control can be done with gears.


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## spinman1949 (Jun 29, 2009)

*Electric drill*

You could purchase an electric drill with variable speed. Use the speed control from it. Check the Amp and Wattage rating on the drill to make sure it will handle the load of the dayton motor.


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## fritz42_male (May 5, 2009)

Kits are available:

http://www.electronickits.com/kit/complete/motor/vek2636.htm

http://www.quasarelectronics.com/smart-kit/1074-ac-motor-speed-controller-230vac.htm

http://www.jaycar.com/productView.asp?ID=KC5478&keywords=speed&form=KEYWORD

These are for brushed motors such as those in electric drills and grinders. If you have a brushless motor then it's more difficult.


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## jaege (Aug 23, 2009)

AC motors are not difficult to speed control, we use VF drives to do it. They are just expensive to speed control. I cant imagine using a VFD to control a little prop motor.


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## bradbaum (Jul 26, 2008)

sorry, but in my book: Expensive = Difficult


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## randyaz (May 26, 2006)

check this out, it might work

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=43060


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## fritz42_male (May 5, 2009)

Brad - what is the motor in or do you know what type it is?

Controlling a brushed AC motor is neither expensive NOR difficult. You can usually find what you wanto at a tool shop for $10-$20


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## Brad Green (Jul 29, 2004)

fritz42_male said:


> Brad - what is the motor in or do you know what type it is?
> 
> Controlling a brushed AC motor is neither expensive NOR difficult. You can usually find what you wanto at a tool shop for $10-$20


The motor I have is the venerable old Dayton 2Z806 6 rpm gearmotor in a FCG rig. I was only looking to slow the ghost's movements down a little without having to replace the motor (Dayton's are pricey!)


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## fritz42_male (May 5, 2009)

It only takes 1/2 amp at 115V - any cheap AC speed controller will do such as the one randyaz posted.


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## hpropman (Jul 27, 2008)

Or you just replace the motor with this motor:

https://www.surpluscenter.com/item.asp?UID=2009090720282593&item=5-1587&catname=electric

4RPM at 12 volts and about 5.5 at 14 volts. Lots of torque it is perfect for the FCG. Easy to solder wires directly to the motor and you can tap a 1/4 bolt into the spline output shaft. The bolt can also be pinned by drilling from the side if needed.


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## Brad Green (Jul 29, 2004)

Thanks for the input, I happen to live within a few miles of a Harbor Freight outlet, so I'll give the router control a try. Again, I appreciate the help!


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## Brad Green (Jul 29, 2004)

I'l probably get laughed outta the room for this, but would a simple dimmer switch controlling an outlet accomplish what I'm looking for, or would the motor's amp/voltage requirements be too great a strain?


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## fritz42_male (May 5, 2009)

Theoretically yes - both use a Triac to control the motor but the way the dimmer 'chops' the AC waveform will be different. A fan speed switch may possibly work but the router control is your best bet.

If you have to try a dimmer switch I'd suggest a leading edge dimmer. Dimmer switches can cause AC motors to stall and will generally only work for about 1/4 the speed range of a motor speed control.


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## Gothyc Designs (Dec 30, 2006)

So would the router controller work to decrease the speed in 12v wiper motor? I have one of those router controllers. it actually sucks for making my router variable, so I don't use it anymore. I might have to play around with that. But would like to hear thoughts on it.

ThX


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## fritz42_male (May 5, 2009)

I've never tried it so not sure - in any case I run my routers at full speed (warp factor 5 Mr Sulu!).

With DC motors, you want an actual voltage change although below certain levels you will lose a lot of power. The best way of controlling the speed of a DC motor is with a combination of voltage AND something called pulse width modulation and I'm playing around with a picaxe chip and FET to do this. However, there are plenty of kits out there. Once again the omnipotent Scary Terry has done all the work for us (thanks Terry). Have a look here and I hope it's of use.

http://www.scary-terry.com/wipmtr/wipmtr2.htm

A simple solution might be to connect a bulb in series with the motor or to use a lower voltage supply. I'm trying a 1.5A 5V supply that I got from DealExtreme but it might not have enough current when the prop is under load.


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## Gothyc Designs (Dec 30, 2006)

thats what I was thinking that the router controller may not allow enough power to use it.
I'll look over Scary Terry's link. I've recently looked there, but was looking for other info for another prop.....lol. I guess I could check with radio shack if they have potiemeters that may be of use.

The prop I'm making is a skeleton stirring a cauldron. and the wiper motor seems still fast at its lowest speed I found on it.

Thx !!


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## fritz42_male (May 5, 2009)

If you have a 4.5V battery pack or 6V lantern battery, try the speed with that (no load though - just run the motor without the stirrer). If that speed is OK for you (& most wiper motors will run at 2 speeds) then a 5V supply such as the dealextreme one or 5V from a hacked PC power supply should do fine. Some PC power supplies with do 3.3V as well - slower again.

I just tested my zombie grabber (4 bar unit) with a 3xAA battery pack so I could play with the various arm and crank positions. Worked as long as there was little friction. Once I get the movement right I'll try it with the dealextreme PSU.

I just found a slightly better 5V supply - http://www.dealextreme.com/details.dx/sku.28773 5V @ 2A from any AC input and only $4.85 free shipping!


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## Doc Doom (Aug 28, 2008)

I may be showing my ignorance but what about wiring in a dimmer switch or using one built into an extension cord?

Guess I really am showing my ignorance, didn't see previous post.


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