Any tricks to make an AC motor run backwards?
T Chap
Posts: 4,223
I have a drill press that I use for tapping parts. It is an typical AC motor with a belt and pulleys to set speeds. Does anyone know any methods to make an AC motor run both directions? I don't do enough to warrant buying the expensive (1000$) tap system.
Comments
If the motor has two leads, there's not much you can do.
-Phil
I don't see any info that states if it is an induction, looks like a regular DC motor. I would need to have the polarity switchable. Is the field coil something that must be removed and flipped or can I add wires and a switch to flip it external of the motor?
That would have been what's called a "universal" motor. So named because they work on DC supply too. They are ordinary electro-magnet DC wound motors but have the stator and rotor windings wired in series with each other. Their downside is lack of speed regulation.
T Chap,
A cheap single-phase drill press is more likely to use a capacitor-run induction motor to get the speed stability.
Looking at the picture, the motor proportions is typical of an induction motor. So there should be a capacitor somewhere. It maybe near the power switch. The capacitor connects to a second winding in the induction motor.
In both cases though, to reverse direction, just one of the two windings needs reversed. Either winding reversed works as good as the other, but it can't be both together. To do this you have to find the separate connections of those two windings. Some designs terminate the windings at a terminal block, this makes it much easier to do.
If you reverse the motor in a table saw, does it join wood together instead?
Lost in Space clearly demonstrated to me at an early age that anything can be undone by reversing the polarity.
Sorry for derailing thread. kwinn's "abnormal forum behavior" in action.
No problem erco. I think we are all used to your abnormal behavior.
http://www.grizzly.com/products/Tapping-Attachment-MT-2/T10057
It automatically reverses the spin of the tap.
Bean
Edit: pulley... belt... Just twist whatever's twistable.
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Regarding the three leads to the motor, since one of them is ground, DO NOT SWAP LEADS to try to make the motor go in reverse. IT'S NOT A THREE-PHASE MOTOR, and you could risk electrocution by doing so.
-Phil
Is it not simply a matter of reversing the START winding of the single phase induction motor?
Single phase induction motors will run equally well in either direction once they have started. If you were to connect only the RUN winding to AC, it just doesn't have a bias to get the thing going. If you then give it a good spin by hand, it will then pick up speed in that direction.
So it seems to me, a double pole double throw reversing switch on the START winding is all that is needed. The START winding is de-energized by a centrifugal switch once the motor gets up some speed.
Be sure NOT to throw the revering switch while the motor is still spinning (in either direction) as that will surely blow out your START winding. That winding is sized to operate only momentarily, and not frequently.
Cheers,
Peter (pjv)
-Phil
The following article shows the many ways your motor could be originally constructed and the options you could have to reverse its rotation.
woodgears.ca/motors/reversing.html
From your last photo, I can clearly see what seems to be a centrifugal switch. The starter winding is in series with it.
We can't see a capacitor, but there are other ways to get the motor running in the proper direction, including a series resistor or even a starter winding having an intrinsic increased series resistance by itself.
First, you should focus in getting access to both terminals of the starter winding, inside the motor, then you could proceed with the motor rotation reversal.
Carefully remove the back plate and follow the article directions to verify your motor could be easily reversed, or not.
Hope it helps.
Henrique
And how to you implement the "two steps forward, one step back to break the chip" required by many tapping protocols? This would seem to require finer control than a purely electrical solution can provide.
-Phil
Phil, I can stop the tap easily by killing the power switch so there is minimal ramp down time to stop, partly because it is very geared down.
- haha, no. I re-purposed the motor and needed direction control for a remote control car I was building.
It's not true, unfortunately; I tried playing a country/western record backwards, my daddy DIDN'T get out of jail, my dog DIDN'T spring back to life and my whisky bottle DIDN'T fill up!