Any tricks to make an AC motor run backwards?

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.
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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 21,403
    edited November 30 Vote Up0Vote Down
    Does the motor have three leads and a capacitor connected to two of them? If so, just switch one end of the cap to one of the other leads. (This would be atypical for a drill press, though.)

    If the motor has two leads, there's not much you can do.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • I don’t see any caps. Just the main 3 conductor cable into the motor.
  • if it isn't an induction motor, you can swap the field coil polarity.... I did this for a re-purposed table saw motor.



    Beau Schwabe -- Submicron Forensic Engineer
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    Seriously at this point in the game the ship has sailed and "I have no expectations" <- said someone we know
  • https://www.lowes.com/pd/PORTER-CABLE-8-Amp-12-Speed-Floor-Drill-Press/1000132463

    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?
  • evanhevanh Posts: 4,430
    edited November 30 Vote Up0Vote Down
    if it isn't an induction motor, you can swap the field coil polarity.... I did this for a re-purposed table saw 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.

    The Prisoner's Dilemma, in english - "Selfishness beats altruism within groups. Altruistic groups beat selfish groups." - Quoted part from 2007, D.S Wilson/E.O Wilson.
  • if it isn't an induction motor, you can swap the field coil polarity.... I did this for a re-purposed table saw motor.

    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.

    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • erco wrote: »
    if it isn't an induction motor, you can swap the field coil polarity.... I did this for a re-purposed table saw motor.

    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.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • There are no caps on the motor, only 3 wires to the motor. Green>Ground Hot and Neutral.
  • If it's a three phase motor swapping any two leads will make it run in reverse. Otherwise you should be able to change leads in the connection block of the motor.
  • BeanBean Posts: 7,815
    edited November 30 Vote Up0Vote Down
    Can you use something like this ?
    http://www.grizzly.com/products/Tapping-Attachment-MT-2/T10057

    It automatically reverses the spin of the tap.

    Bean
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    Esterline Research & Design
    thitt@esterlineresearch.com

    We offer consulting on the following areas of expertise:
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  • SeairthSeairth Posts: 2,252
    edited November 30 Vote Up0Vote Down
    Another low-tech solution that's both cheap and doesn't require modification of the press might be to introduce half a twist in the belt (you might need a slightly longer pulley for the "reverse"). As this is for tapping, I'm assuming this is all at very low RPMs, so it shouldn't be too much of an issue if the twisted pulley rubs against itself.

    Edit: pulley... belt... Just twist whatever's twistable. ;)
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 21,403
    edited November 30 Vote Up0Vote Down
    Seairth wrote:
    Another low-tech solution that's both cheap and doesn't require modification of the press might be to introduce half a twist in the pulley (you might need a slightly longer pulley for the "reverse"). As this is for tapping, I'm assuming this is all at very low RPMs, so it shouldn't be too much of an issue if the twisted pulley rubs against itself.
    I was going to post that myself -- half twist in the belt, not the pulley, though. But when I realized it was for tapping, he needs to be able to go forward to tap the hole, then in reverse to withdraw the tap. Having to switch belts to switch directions would be impractical.
    _______________

    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
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • I thought about belt configurations already there is no easy way to flip forward and reverse so twisted belt won’t work short of designing some crazy method to “drop in” that can switch. Most clutch based add one like bean shows are 900 and up so I never bothered but for 180 that’s worth it for a test. As far as reversing leads on the motor I don’t think that’s an option on an AC motor. A thought was to retrofit a dc motor but that’s a lot of work to make it fit.
  • Hey,

    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)
  • Posting a picture of the motor data plate or connection would be helpful. What is the motor HP, Voltage, Amps, RPM, etc.? Most small non cap. motors have a centrifugal switch to kick out the start winding. You could buy a VFD drive for small motors fairly cheap it would give you reversing and speed control. That depends on the motor type. A 1/4 hp VFD will run you about $50-$60 bucks new.
  • Checkout Invertek VFD's for single phase motors
  • Here is the motor from the bottom. No cap visible.
  • Have you investigated eBay for Tapmatic reversible tapping heads? You don't need to spend a thousand bucks for one.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • Hi T Chap

    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
  • The motor does have a capacitor so it should be reversible with a DPDT switch.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • One problem I see, even if you can reverse the motor is "runout." Even though you disconnect power to the motor, it will not brake immediately. This could cause a problem for tapping, a problem the commercial tapping attachments solve with the use of a clutch.

    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
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • Oops, picture too big. Here is the resized one.
    1725 x 2316 - 723K
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Interesting! It DOES have a capacitor, thanks kwinn I just checked it out. And I can see and hear the centrifugal switch working when it turns on and off. That is encouraging, I will take the motor apart tomorrow hopefully and see if it allows access to both windings. The video posted above shows that some motors use only 3 wires and cannot be reversed because it is too difficult to dig in and separate the windings.

    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.
  • That was a good video Yanomani . Looks like a lot of work to pull the motor out and rework it.
  • I only drill 1” delrin(plastic). You don’t need multiple steps. Reversing off the 3/8 tap is a chore and is a good 2 hand workout 3/8-16 is 16 full turns plus extra so it’s more like 25 full turns to remove the part.
  • Got the motor apart easily. 2 red (top) are to the cap. 2 red (lower) are to the centrifugal switch. 2 Black (right) are out of the case to the black and white main wires in. Starting to see what wires to cut and flip
  • It works! Thanks guys for the info on this and especially that video. Learned a lot about motors today.
  • Just tried tapping parts. Works like a charm. Wish I had of figured this out 10 years ago.
  • Beau SchwabeBeau Schwabe Posts: 6,308
    edited December 1 Vote Up0Vote Down
    T Chap wrote: »
    Just tried tapping parts. Works like a charm. Wish I had of figured this out 10 years ago.
    - Awesome, glad you got it working


    erco wrote: »
    If you reverse the motor in a table saw, does it join wood together instead?
    - haha, no. I re-purposed the motor and needed direction control for a remote control car I was building.




    Beau Schwabe -- Submicron Forensic Engineer
    www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

    Seriously at this point in the game the ship has sailed and "I have no expectations" <- said someone we know
  • erco wrote: »

    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.

    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!
    PropBASIC ROCKS!
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