Making an AC drill motor run faster

Discussion in 'General Electronics Chat' started by cmartinez, Aug 23, 2017.

  1. cmartinez

    Thread Starter AAC Fanatic!

    Jan 17, 2007
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    I purchased a couple of 100VAC, 600RPM heavy duty drills a while ago, and I'd like to see if it's possible to make them run faster. The motors are of the universal brushed-type, with the stator and the rotor connected in series.

    Short of changing their gear ratio, is there an electrical trick out there that I could use to make them run faster? Preferably at twice their rated speed. Something tells me there's no practical way of doing that, but I'm asking just to make sure.

    @MaxHeadRoom
     
  2. tranzz4md

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    Apr 10, 2015
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    Oh, there are plenty. Not all of them would cost more than a new drill motor. Some of them might not even cost much more than a used drill motor from a pawn shop or thrift store.

    You could use one to turn the other, but it wouldn't quite get you 1200 rpm, because you'd run out of cord before it got anywhere near full speed.

    Also, any trix increasing the speed will not increase power, so your drill motor will probably need help to achieve that newfound rate of rotation under any significant load, like, oh, touching something with that drill bit in the drill chuck. Help like pulling a looooong ripcord really fast, or you running around in circles,,,, really fast.

    Post the video if you get a chance.
     
  3. cmartinez

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    I'm afraid I don't quite understand what you said there... and btw, the drills are being used for a very light application, and I doubt that even 20% of their full power capability is being used during normal operation.
     
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  4. Ylli

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    You may be able to get a bit more speed by shunting the field with a resistor. But running the rotor at much more than its rated RPM may end up throwing the windings off.
     
  5. tranzz4md

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    Really I was joking, it's a weakness of mine.

    But (a bit more) seriously, the short, boring answer is:no.

    Those drill motors are voltage dependant, but the typical do-it-yourself attempted trick of attempting to run something like that by "hooking it up to 220" only results in smoking, burning parts, as does any use of frequency control devices.

    Seriously, sell them to help finance the purchase of the correct tool.
     
  6. cmartinez

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    Yeah... I was afraid that was going to be the answer. And no, I wasn't considering running them at a higher voltage. I'm quite aware of what would happen.
     
  7. cmartinez

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    Here's a simplified schematic of both the stator and rotor windings. Where do you propose to connect said resistor?

    Capture.PNG
     
  8. MaxHeadRoom

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    Is the 600 rpm after gear reduction? I would assume so.
    If it is and the base rpm of the motor is already high, they only tolerate about 20krpm.
    Increasing the voltage, increases the rpm the current stays low and is dependent on load, but the rpm may exceed the bearing rating and centrifugal forces on the armature.
    Anything over around 22krpm is about the limit.
    Max.
     
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  9. cmartinez

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    I'll see if I can measure the armature's rpm and get back to you. Thanks!
     
  10. BR-549

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    I would try a sine wave inverter.......or what they use to call a variable frequency drive. Analog, not PWM. The ones I worked with.....you could very the voltage and the frequency. Single phase and 3 phase. You could also set current limits to protect the motor while experimenting. You certainly have the skill to build one. But if you know someone in a industrial maintenance area....you might scrounge a small one.

    My knowledge is old.....maybe everything is PWM now.
     
  11. dendad

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    Although I would not really recommend it, try a suitable bridge rectifier and decent sized electrolytic capacitor to run it on DC. As they are "universal" motors, DC will be ok. That will raise the effective supply volts a bit but most probably decrease the life too.
    Stand well back ;)
     
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  12. cmartinez

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    Not a bad idea, except I couldn't be 100% sure what direction the motor would turn when I started it...
    On the other hand, maybe I could connect it to 220vac and pwm it... (or phase-angle control with a triac) see how fast I can make it turn before it starts to heat up...
     
  13. dendad

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    The direction the motor will turn depends on the field/armature connections phasing, not the power supply. AC or DC does not matter with these motors. Otherwise, when on AC, it would just tremble and not turn.
     
    Last edited: Aug 24, 2017
  14. MaxHeadRoom

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    On these motors the rpm increases due to field (total) current Lessening not Increasing, the real danger is increasing the rpm past the point that it was manufactured to withstand, centrifugal limits etc.
    You are probably not going to get twice the present rpm though.
    Max.
     
  15. shortbus

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    May be wrong about modern drills, but older ones used the same motor for all different output speeds. The difference was in the gear train after the motor.
     
  16. cmartinez

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    If that's true, then this motor should be running at about 4,000
     
  17. shortbus

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    Like I said this is based on older drills. With the modern vary speed ones I think you'll find the gearing is set up so the highest speed is with full power applied, and then the lower speed are made by electronically slowing the motor down. What drill motor are you working with? There are some sites showing the internal parts that may have different internal gears available. But in trying to repair stuff like this over the years, usually a new tool can be bought cheaper than internal parts.
     
  18. cmartinez

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    It's a Milwaukee 4253-1, I posted the link in the very first message of this thread
     
  19. Ylli

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    Shunt the field, whichever one that is. You want to reduce the strength of the field.
     
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  20. MaxHeadRoom

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    There are a pair of field windings usually, opposite sides of the armature.
    Max.
     
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