I have here a small electric motor that used to power the fan in an old slide-strip projector. I’d like to use the motor for something else, but I need it to be going a lot slower. What governs the speed at which an electric motor turns - voltage or amps?
Hi s1m0n
Is it an A.C. or D.C. motor?
If A.C. then you will need to use a gearing system.
If it is D.C. then lowering the current going into the motor should do it.
David
If the motor runs on DC then voltage governs the speed.
You can use a rheostat (variable resistor) to reduce the voltage, or with a speed controller using a MOSFET semiconductor.
In my PC I reduced the cooling fan speed by putting it onto 5V instead of 12V (and checking that the PCU chip did not overheat).
If it is an AC motor then the speed is controlled by the frequency of the AC.
Speed controllers on variable speed power tools use this.
But the motor need to be an induction motor, not synchronous motor.
It need to have brushes. Synchronous motors don’t have brushes.
You can buy speed controllers, like here:
http://www.quasarelectronics.com/cr0008.htm
Dimmer switches are not good enough for motors.
Hmmm. I also have a motor & variable-speed foot pedal off an old Singer sewing machine, similar to these:
Whereas the motor I mentioned first is nearly identical to this:
If I’m following, the bottom one is an a/c motor that runs on 10 amp /110 volt current, while the upper is an induction motor with brushes somewhere inside that housing. The serial no plate says v.110-120.A.O.8.A.C. & D.C., which I translate to mean that it’s also 110V but doesn’t care whether I feed it AC or DC. Is that correct? What might A.0.8 signify?
Simon, the top one should be able to run on both AC and DC.
The bottom pic looks like a synchronous motor, no brushes. In which case you won’t be able to vary the speed.
I was wrong, the bottom one is a shaded pole motor:
see http://en.wikipedia.org/wiki/Shaded-pole_motor
which is a type of simple induction motor, and can be controlled with TRIAC-based variable speed controls.
Thank you; this has saved me a lot of guesswork and frustration.
The line frequency would govern the speed. There are controller that vary the line frequency in Hertz (Hz) that would control that type of motor.
An AC/DC Motor can be controlled using a Variac. They used to be quite expensive but they are more common today and can be found on Ebay at a reasonable price.
Also, you can buy motor and drive combo sets pretty cheap from Suplus Center in Lincoln NE.
https://www.surpluscenter.com/home.asp
Actually, what I’m trying to do is slow it down a lot, not speed it up. I need to change it from cooling fan speed to mirrorball rotating speed.
I don’t think you can achieve that much speed change with an electronic device. Think how difficult it is to get slow speeds with the speed trigger on a variable speed power drill. You need to use mechanical gears to get to rotation speeds of under a second per turn. You may also be able to use a motor with much less power, so depending on the exact purpose I would look for a smaller geared motor, perhaps a small DC servo motor used in model boats and planes.