Groups »
Forums »
Answers »

Featured Groups

  • Bare Conductive
  • Drawing and Art
  • Sustainability
  • 123D
  • Fenix Intl, Ready Set Off The Grid
  • Featured Authors
  • 3D Printing

COMMUNITY : FORUMS : SQUARE PEGS

New Forum Topic

Speed Control for AC Electric Motors

Can anybody tell me how to build a controller to adjust the speed of an 110VAC electric motor, ( ex: blower motor, fan motor ) I was cautioned about using a light dimmer. bill

sort by: active | newest | oldest
dcronje says: Mar 25, 2013. 2:25 PM
Hi, I was wondering if anyone would be able to help me. I have a question. I have two motors, each being 3 phase. The bigger motor runs the main machine in the plant and the second motor runs a screw conveyor feeding the first Motor. I need a way to regulate the input to the bigger motor by slowing the speed of the smaller motor or speeding it up if the load on the bigger motor is high or low respectively. Would this be possible by somehow setting a level on amperage of the bigger motor to keep the amps at the highest possible operating efficiency. My big motor is 75kw and the smaller is 2.2kw
424 bant says: Aug 31, 2012. 6:30 AM
Do you know about ECM motors, these will allow you to have a true variable spped motor for your furnace, this will also give you the same performace as a DC motor as far as electric usage is concerned.
nucleargungus says: Dec 3, 2010. 4:33 PM
is this motor a universal motor or capacitor start/run?
2
jtobako says: Mar 6, 2007. 5:00 PM
some light dimmers will work with some motors : ) sorry, that's what i've found experimentaly when trying to control the speed of a blower. why? i think (but i'm not sure) that the cheeper light dimmers use a voltage chopper to limit the amount of each AC pulse-fine for incandecent bulbs but not effective with a motor. i believe that a resistace based control will work with a universal motor (one with brushes).
17
LasVegas in reply to jtobakoMar 6, 2007. 7:55 PM
Yes. It may work. But not safely. It will eventually burn out the motor. A Dual-phase motor can be speed controlled by adjusting the phase between coils by changing the size of a capacitor or a more complicated circuit to adjust the phase with a potentiometer. You can find circuits like these on quality ceiling fans.
BGreenHVAC in reply to LasVegasNov 11, 2010. 1:38 AM
I may be misunderstanding what you are saying, but Dual-phase makes no sense. Single-Phase and 3-phrase are electrical terms that express the sine wave in an oscilloscope. The windings on a 3-phase generator are off-set 120° to produce 3 separate currents in the same set of wires.

The Sine wave illustrates the positive and negative voltage as it is being produced. A "dual-phase" would have a positive and negative electromotive force Simultaneously and cancel itself out. Therefore no current would be produced.

I have only heard the term "Dual-Phase" as a joke. It is what we tell people to confuse them. We ask a new guy to find a 2 phase or dual phase component. No matter how much they look, there is only single and three phase.

Are you talking about a 2 speed motor perhaps?
13
steveastrouk in reply to BGreenHVACNov 21, 2010. 11:41 AM
Your US electrical supply could be described as "two phase", as there is 180 degree phase difference from hot to hot and since sure as hell, if you connect from hot to hot in your breaker panels MUCH more than "no current" would flow.
17
LasVegas in reply to BGreenHVACNov 11, 2010. 11:32 PM
A Single-phase AC motor, without some method of starting, will just sit there when power is applied. Manually starting the rotation in either direction would allow the motor to run in that direction. There are a few techniques used to start an AC motor including the use of a capacitor to produce a second line 90 degrees out of phase with the original phase. This is applied to a second winding to give practical torque at startup. Often this second phase is turned off soon after the motor is started and sometimes the motor runs continuously with two phases. Frequently, motors are speed controlled using a similar technique.

Reference: http://en.wikipedia.org/wiki/Two-phase_electric_power
BGreenHVAC in reply to LasVegasNov 13, 2010. 12:19 PM
Thanks for the input. There is a difference in terminology. What Wikipedia's article refers to as 2 phase is what my industry refers to as "leg of power" After investing hours of reading, I have come to the conclusion the terminology was changed to prevent confusion between the concepts.
I took the information literally. The actual information is the same, however the terminology is very different.

I appreciate your information. Thanks.
2
jtobako in reply to LasVegasMar 7, 2007. 7:35 AM
well, 8 years later the fan was replaced with a different system. not because it stoped working, but because where it was being used changed (new forge).
1
panic mode says: Jun 26, 2007. 7:59 PM
as lemonie posted this is why people make VFDs (variable frequency drive) - or some people call it VSD (variable speed drive). they are actually driving 3-phase motors but there is bunch of models that can be powered from single phase (drive produces phases independantly from line). then you can easily set any speed you like. you can overspeed motors as well but eventually torque drops. usable range is good +/-200% of nominal motor speed. note that most motors are not designed to run slow (cooling!) so it's not bad idea to avoid speeds below some 20% or so under load (or add separate small motor that will run fan always at 100% which is not exactly practical, specailly for smaller motors). one alternative is to use DC drive and motor (still powered from 120VAC, drives contain rectifier and control electronics), these drives are much cheaper than VFDs and DC motors have pretty solid torque over wide speed range.
BGreenHVAC in reply to panic modeNov 11, 2010. 1:43 AM
When using a converter to operate a 3-phase motor with a single-phase source, do you lose Amps?
1
panic mode in reply to BGreenHVACNov 11, 2010. 11:58 AM
"When using a converter to operate a 3-phase motor with a single-phase source, do you lose Amps?"

if you have two motors (one is single phase and other is three phase), both running at same voltage with same efficiency and under same load, three phase motor will draw less current per phase so wiring can be smaller gauge.

but i think the question is about energy or efficiency and every time you convert energy, using some system, some of the energy is lost (because efficiency not 100%). VFD drives are no exception.

if you are using 3-phase motor with VFD powered from single phase source to do job of single phase motor, this setup will draw more current from outlet than the single phase motor would.

broham (author) in reply to panic modeJun 26, 2007. 8:35 PM
Thanks, but I didn't understand much of what you said. I just went out and purchased some controllers a while back. Thanks again..
sketchball says: Sep 26, 2009. 11:35 AM
HELP??? I hace a 7 AMP (shaded pole ?) motor from an old vacuum cleaner. Is there an easy and cheap way to control the speed? preferably through a switch or control. Thanks
49
lemonie says: Mar 8, 2007. 5:19 PM
AC motors tend to be tied into the frequenncy of the supply. If you could invesigate a washing-machine's spin-cycle you you might get some useful clues. L
17
LasVegas in reply to lemonieMar 8, 2007. 10:48 PM
Some motors are directly tied to the frequency. Usually the brushless AC motors. I have a SuperSpiel machine (similar to a slot machine) from Germany that I converted for US power and lamps. The conversion went great using a 120:60v transformer hooked up in reverse to supply 240v to the device. The only difference is that the motor and therefore all game functions run 20% faster.
49
lemonie in reply to LasVegasMar 9, 2007. 3:10 PM
Some of the more modern electric trains over here, use an 'electronic' gear-shift. AC motors are more efficient (in this application anyway), and they use frequency shifts, which do actually sound like changing gear.
This link may be os interest to the instructable :
http://en.wikipedia.org/wiki/Variable-frequency_drive
2
jtobako in reply to lemonieMar 8, 2007. 6:15 PM
washing machine motors are built with two speeds (i think mine was 1700 and 1000 rpm roughly), and the transmission gearing takes care of the rest. three speed fans are simmilar, built with three speeds depending on which coils receve power.
105
trebuchet03 says: Mar 5, 2007. 9:08 PM
Variac ;) That might be a good place to start researching :)
Pro

Get More Out of Instructables

Already have an Account?

close

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!