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Re: [multimachine] Re: inductive load dimmer

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  • Charles R. Patton
    ... Watch out! A router speed controller will probably be totally unsuitable for use on AC induction motors due to unsymmetrical waveforms and/or undersized
    Message 1 of 18 , Jan 10, 2008
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      hepps_29646 wrote:
      >Has anyone suggested a router speed controller?

      Watch out! A router speed controller will probably be totally unsuitable
      for use on AC induction motors due to unsymmetrical waveforms and/or
      undersized for AC induction motors

      One might class motor in about 4 classes:
      1) brush machines such as routers, quills, vacuum cleaners, sewing
      machine, Dremel tools, etc.

      AC induction motors:
      2) shaded pole such as electric clocks, small aquarium pumps, ceiling
      fans, small table fans, etc.
      3) centrifugal start such as most single machine tool ½ to perhaps 10 hp.
      4) 3-phase such as in industrial tools like lathes, mills, grinders,
      bandsaws, etc

      There are a lot more ways of differentiating, but for this discussion
      allow me some leeway.

      Now small light dimmers and likely a router controller can be highly
      unsymmetrical in the power they supply—i.e., they can have a large DC
      component. Light bulbs and brush machines don’t care. AC or DC they run
      pretty much the same. Generally however a brush machine is chosen for
      its application because they can run at very high RPM’s, although not a
      huge amount of torque.

      The other three classes require symmetrical AC waveforms that can be
      generated by special controllers. There are a few such controllers that
      are labeled for use with transformer driven lights such as used for
      track lighting, but these will be too low in power capability for
      machine tool use. All three AC induction machines (non-brush types)
      depend on a rotating field to start.

      The shaded pole has flux build-up that is not in phase with the main run
      winding and is physically rotated from the main pole (look for the heavy
      copper strap or wire around a part of the stator pole.) This condition
      is always present but only used on small motors due to the loss of this
      small strap acting as a shorted turn carrying (large) currents which
      adds considerable ohmic loss… If you don’t believe me, touch one of
      these shaded poles on a fan motor that has been running for a while, but
      don’t blame me for the burned finger that results. This type of
      construction is unsuitable to large motor due to the increasing loss and
      relatively poor starting torque.

      The standard centrifugal start improves on this phase generating
      technique by use of more (or a lot more) current or the additional use
      of capacitors to give even more phase difference and starting torque,
      but again these windings cannot run in a continuous mode without burning
      up. But as already mentioned by a previous poster, the centrifugal
      start-up switch opens this circuit moments after start-up when speed is
      sufficiently high for the single-phase rotor to generate its own phase
      shift (a simplification to be sure, but this isn’t going to be a full
      course on motors.) The important point is that a single phase machine
      cannot generate torque when the rotor is stopped with the main winding
      only (excluding capacitor-run motors.) The rotor has to be turning to
      generate torque. Hence the specification of “drop out” torque. Exceed
      this and the rotor stalls and torque falls as the rotor speed decreases
      until the centrifugal switch kicks in again.

      A three phase machine has the easiest time of it. Three windings
      physically 120 degrees apart and driven by 3-phase power automatically
      create a rotating field that has high torque. The current is high as the
      rotor is not at speed generating back EMF, but this also corresponds to
      high torque. Very large machines will have controllers that reduce the
      starting current for either safety of the machine or the power grid in
      the factory supplying it. Since there is no throw-out switch as in a
      single-phase machine, and the torque exists even if the rotor is locked,
      then 3-phase machines can run over very large speed ranges if driven by
      variable frequency drive controllers.

      Now back to the main point – an AC induction machine driven by a
      controller with a DC component can lead to total or partial saturation
      of the stator. What this means is that the machine will draw abnormal
      amounts of power producing no useful torque. Remember that a very useful
      technique for stopping AC motors is to remove the AC line and put DC
      current through the stator windings, so DC while its running is the
      equivalent of simultaneously putting your foot on the brake and the
      accelerator in a car. Not good for the brakes, engine, performance or
      mileage.

      So I guess this boils down to my suggestions.
      Only try to speed control 3-phase motors unless you can use a high-speed
      brush motor in your application. Check out Ebay for a whole series of
      them under the search term “variable frequency AC drives” to see some
      representative controllers. The input is pretty much disconnected from
      the output as the input is typically rectified and filtered to power the
      3-phase power output circuitry. So the input choice is more governed by
      the source power constraints where the input requirements move to
      3-phase and higher voltages at higher power levels to lessen the problem
      of large wire gauge feeding the controller.

      Regards,
      Charles R. Patton
    • Lance
      Just a note of experiential confirmation. I have tried the router speed control and other simple (cheap) speed controls on an 120V 2 HP AC pump motor trying to
      Message 2 of 18 , Jan 10, 2008
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        Just a note of experiential confirmation.
        I have tried the router speed control and
        other simple (cheap) speed controls on an 120V 2 HP AC pump motor trying to make it
        variable speed. The smoke comes out in about 3 sec.

        The solution was to find a throw-away treadmill and scavenge the variable
        speed 2 HP motor from it.  March should be a good month to check
        Craig'slist for treadmills. People's New Year's resolution to exercise
        should last maybe 3 months.

        lance
        *****
        On Jan 10, 2008, at 7:41 PM, Darwin Wandler wrote:

        I will repeat this "NO" will work on an ordinary single phase motor.
        Ceiling fan motors are made with no start windings or capacitors and wound
        specificly for low power 1/4 HP or less variable input AC waveform.

        Router motors have higher HP and are essentially a special wound AC motor,
        simulating a DC motor with its characteristics. Home Shop Machinist 
        had an
        article a few months ago on AC motors and VFD drives which explained how
        to made an AC motor with variable drive control as used in drills, 
        routers, jigsaws
        etc.

        If you connect your 3HP single phase AC induction motor to a dimmer control
        start your stopwatch because only seconds will pass before smoke puffs out
        and it stops instantly. You should hear the sizzle of insulation just in 
        time to click the
        stop watch off.

        Darwin


      • robdawrench
        Scott, A dimmer type switch cannot handle the current full stop and is not designed to, what is required is a reostat type switch which will handle the
        Message 3 of 18 , Jan 10, 2008
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          Scott,

          A dimmer type switch cannot handle the current full stop and is not
          designed to, what is required is a reostat type switch which will handle
          the currents involved due to the way it is constructed, (a varistat
          transformer could aslo be used intead) or what about a electric drill
          type motor or a flymo motor (electric hover mower) as these are a
          universal type motor in a lot of cases and will run on ac current so
          will take ac or dc type voltage and are easily controlled on ac or dc
          current, so as speed can be as well.




          --- In multimachine@yahoogroups.com, Darwin Wandler <wandler@...> wrote:
          >
          > Rule of thumb start current instantaneous surge is 10 to 20 times
          rated
          > full load
          > run current. The reason breakers don't blow is they use a resistive
          > current detection
          > method which takes a few seconds to heat before tripping. Surge
          current
          > lasts for
          > less than 1 second in most cases. Fuses are instant blow so they can
          not
          > take
          > start current. You need motor fuses which are encased in
          silicon/ceramic
          > sand
          > to take the heat away on surge current yet blow on short circuit.
          >
          > Darwin
          > cvlac wrote:
          > >
          > > Hi Scot
          > > My motor is just a single phase 3hp one!
          > > Do you think that something can be made with this dimmer?
          > > Any way I need too a current delimiter for the start up of the motor
          > > because I have a 15 A fuse and seems that the motor absorbs more
          than
          > > that at start up .Any suggestion ?
          > > Costas
          > >
          > >
          >
        • jacques savard
          ... that what we call serila motor in electronic science variable speed rotor in serie whit the stator ... that is squerel cage motor can be veriable speed
          Message 4 of 18 , Jan 10, 2008
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            > hepps_29646 wrote:
            > >Has anyone suggested a router speed controller?
            >
            > Watch out! A router speed controller will probably be totally unsuitable
            > for use on AC induction motors due to unsymmetrical waveforms and/or
            > undersized for AC induction motors
            >
            > One might class motor in about 4 classes:
            > 1) brush machines such as routers, quills, vacuum cleaners, sewing
            > machine, Dremel tools, etc.

            that what we call serila motor in electronic science variable speed rotor
            in serie whit the stator

            >
            > AC induction motors:
            > 2) shaded pole such as electric clocks, small aquarium pumps, ceiling
            > fans, small table fans, etc.

            that is squerel cage motor can be veriable speed by voltage change
            > 3) centrifugal start such as most single machine tool ½ to perhaps 10 hp.

            taht ia cold be lot of modell soem a shunt type other have start coil....
            > 4) 3-phase such as in industrial tools like lathes, mills, grinders,
            > bandsaws, etc

            thia one a syscro motor syncro whit 60 hz
            jack 47'N 71'W
            >
            > There are a lot more ways of differentiating, but for this discussion
            > allow me some leeway.
            >
            > Now small light dimmers and likely a router controller can be highly
            > unsymmetrical in the power they supply—i.e., they can have a large DC
            > component. Light bulbs and brush machines don’t care. AC or DC they run
            > pretty much the same. Generally however a brush machine is chosen for
            > its application because they can run at very high RPM’s, although not a
            > huge amount of torque.
            >
            > The other three classes require symmetrical AC waveforms that can be
            > generated by special controllers. There are a few such controllers that
            > are labeled for use with transformer driven lights such as used for
            > track lighting, but these will be too low in power capability for
            > machine tool use. All three AC induction machines (non-brush types)
            > depend on a rotating field to start.
            >
            > The shaded pole has flux build-up that is not in phase with the main run
            > winding and is physically rotated from the main pole (look for the heavy
            > copper strap or wire around a part of the stator pole.) This condition
            > is always present but only used on small motors due to the loss of this
            > small strap acting as a shorted turn carrying (large) currents which
            > adds considerable ohmic loss… If you don’t believe me, touch one of
            > these shaded poles on a fan motor that has been running for a while, but
            > don’t blame me for the burned finger that results. This type of
            > construction is unsuitable to large motor due to the increasing loss and
            > relatively poor starting torque.
            >
            > The standard centrifugal start improves on this phase generating
            > technique by use of more (or a lot more) current or the additional use
            > of capacitors to give even more phase difference and starting torque,
            > but again these windings cannot run in a continuous mode without burning
            > up. But as already mentioned by a previous poster, the centrifugal
            > start-up switch opens this circuit moments after start-up when speed is
            > sufficiently high for the single-phase rotor to generate its own phase
            > shift (a simplification to be sure, but this isn’t going to be a full
            > course on motors.) The important point is that a single phase machine
            > cannot generate torque when the rotor is stopped with the main winding
            > only (excluding capacitor-run motors.) The rotor has to be turning to
            > generate torque. Hence the specification of “drop out” torque. Exceed
            > this and the rotor stalls and torque falls as the rotor speed decreases
            > until the centrifugal switch kicks in again.
            >
            > A three phase machine has the easiest time of it. Three windings
            > physically 120 degrees apart and driven by 3-phase power automatically
            > create a rotating field that has high torque. The current is high as the
            > rotor is not at speed generating back EMF, but this also corresponds to
            > high torque. Very large machines will have controllers that reduce the
            > starting current for either safety of the machine or the power grid in
            > the factory supplying it. Since there is no throw-out switch as in a
            > single-phase machine, and the torque exists even if the rotor is locked,
            > then 3-phase machines can run over very large speed ranges if driven by
            > variable frequency drive controllers.
            >
            > Now back to the main point – an AC induction machine driven by a
            > controller with a DC component can lead to total or partial saturation
            > of the stator. What this means is that the machine will draw abnormal
            > amounts of power producing no useful torque. Remember that a very useful
            > technique for stopping AC motors is to remove the AC line and put DC
            > current through the stator windings, so DC while its running is the
            > equivalent of simultaneously putting your foot on the brake and the
            > accelerator in a car. Not good for the brakes, engine, performance or
            > mileage.
            >
            > So I guess this boils down to my suggestions.
            > Only try to speed control 3-phase motors unless you can use a high-speed
            > brush motor in your application. Check out Ebay for a whole series of
            > them under the search term “variable frequency AC drives” to see some
            > representative controllers. The input is pretty much disconnected from
            > the output as the input is typically rectified and filtered to power the
            > 3-phase power output circuitry. So the input choice is more governed by
            > the source power constraints where the input requirements move to
            > 3-phase and higher voltages at higher power levels to lessen the problem
            > of large wire gauge feeding the controller.
            >
            > Regards,
            > Charles R. Patton
            >
            >
            >
            >
            >
            >
            > Yahoo! Groups Links
            >
            >
            >
          • hepps_29646
            Charles, Thank you for what seems to me to be an excellent explanation of the types of electrical motors. As you can see I know very little about them. Harold
            Message 5 of 18 , Jan 10, 2008
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              Charles,
              Thank you for what seems to me to be an excellent explanation of the
              types of electrical motors. As you can see I know very little about them.
              Harold
              >
              > hepps_29646 wrote:
              > >Has anyone suggested a router speed controller?
              >
              > Watch out! A router speed controller will probably be totally
              unsuitable
              > for use on AC induction motors due to unsymmetrical waveforms and/or
              > undersized for AC induction motors
            • William Dysinger
              Good dissertation Charles! Even trying to give the short explanation takes a fair amount of words! I d like to see what one of those outdrive AC airplane
              Message 6 of 18 , Jan 10, 2008
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                    Good dissertation Charles! Even trying to give the short explanation takes a fair amount of words!
                I'd like to see what one of those "outdrive" AC airplane motors sized up would do but I know the back EMF would be terrible!
                william(tinkerbill)

                On Thu, 2008-01-10 at 15:43 -0800, Charles R. Patton wrote:
                hepps_29646 wrote:
                 >Has anyone suggested a router speed controller?
                
                Watch out! A router speed controller will probably be totally unsuitable 
                for use on AC induction motors due to unsymmetrical waveforms and/or 
                undersized for AC induction motors
                
                One might class motor in about 4 classes:
                1) brush machines such as routers, quills, vacuum cleaners, sewing 
                machine, Dremel tools, etc.
                
                AC induction motors:
                2) shaded pole such as electric clocks, small aquarium pumps, ceiling 
                fans, small table fans, etc.
                3) centrifugal start such as most single machine tool ½ to perhaps 10 hp.
                4) 3-phase such as in industrial tools like lathes, mills, grinders, 
                bandsaws, etc
                
                There are a lot more ways of differentiating, but for this discussion 
                allow me some leeway.
                
                Now small light dimmers and likely a router controller can be highly 
                unsymmetrical in the power they supply—i.e., they can have a large DC 
                component. Light bulbs and brush machines don’t care. AC or DC they run 
                pretty much the same. Generally however a brush machine is chosen for 
                its application because they can run at very high RPM’s, although not a 
                huge amount of torque.
                
                The other three classes require symmetrical AC waveforms that can be 
                generated by special controllers. There are a few such controllers that 
                are labeled for use with transformer driven lights such as used for 
                track lighting, but these will be too low in power capability for 
                machine tool use. All three AC induction machines (non-brush types) 
                depend on a rotating field to start.
                
                The shaded pole has flux build-up that is not in phase with the main run 
                winding and is physically rotated from the main pole (look for the heavy 
                copper strap or wire around a part of the stator pole.) This condition 
                is always present but only used on small motors due to the loss of this 
                small strap acting as a shorted turn carrying (large) currents which 
                adds considerable ohmic loss… If you don’t believe me, touch one of 
                these shaded poles on a fan motor that has been running for a while, but 
                don’t blame me for the burned finger that results. This type of 
                construction is unsuitable to large motor due to the increasing loss and 
                relatively poor starting torque.
                
                The standard centrifugal start improves on this phase generating 
                technique by use of more (or a lot more) current or the additional use 
                of capacitors to give even more phase difference and starting torque, 
                but again these windings cannot run in a continuous mode without burning 
                up. But as already mentioned by a previous poster, the centrifugal 
                start-up switch opens this circuit moments after start-up when speed is 
                sufficiently high for the single-phase rotor to generate its own phase 
                shift (a simplification to be sure, but this isn’t going to be a full 
                course on motors.) The important point is that a single phase machine 
                cannot generate torque when the rotor is stopped with the main winding 
                only (excluding capacitor-run motors.) The rotor has to be turning to 
                generate torque. Hence the specification of “drop out” torque. Exceed 
                this and the rotor stalls and torque falls as the rotor speed decreases 
                until the centrifugal switch kicks in again.
                
                A three phase machine has the easiest time of it. Three windings 
                physically 120 degrees apart and driven by 3-phase power automatically 
                create a rotating field that has high torque. The current is high as the 
                rotor is not at speed generating back EMF, but this also corresponds to 
                high torque. Very large machines will have controllers that reduce the 
                starting current for either safety of the machine or the power grid in 
                the factory supplying it. Since there is no throw-out switch as in a 
                single-phase machine, and the torque exists even if the rotor is locked, 
                then 3-phase machines can run over very large speed ranges if driven by 
                variable frequency drive controllers.
                
                Now back to the main point – an AC induction machine driven by a 
                controller with a DC component can lead to total or partial saturation 
                of the stator. What this means is that the machine will draw abnormal 
                amounts of power producing no useful torque. Remember that a very useful 
                technique for stopping AC motors is to remove the AC line and put DC 
                current through the stator windings, so DC while its running is the 
                equivalent of simultaneously putting your foot on the brake and the 
                accelerator in a car. Not good for the brakes, engine, performance or 
                mileage.
                
                So I guess this boils down to my suggestions.
                Only try to speed control 3-phase motors unless you can use a high-speed 
                brush motor in your application. Check out Ebay for a whole series of 
                them under the search term “variable frequency AC drives” to see some 
                representative controllers. The input is pretty much disconnected from 
                the output as the input is typically rectified and filtered to power the 
                3-phase power output circuitry. So the input choice is more governed by 
                the source power constraints where the input requirements move to 
                3-phase and higher voltages at higher power levels to lessen the problem 
                of large wire gauge feeding the controller.
                
                Regards,
                Charles R. Patton
                

              • cvlac
                Hi I recently have purchased an angular grinder from a good firm that had this problem too .Then I spoke to the shop and they changed the grinder with an
                Message 7 of 18 , Jan 11, 2008
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                  Hi
                  I recently have purchased an angular grinder from a good firm that had
                  this problem too .Then I spoke to the shop and they changed the
                  grinder with an other one that had a current limiting system at
                  startup, that has no this problem .The new grinder has the same power,
                  but coasted 15 euros more.
                  Costas


                  --- In multimachine@yahoogroups.com, "robdawrench" <woolyondanet@...>
                  wrote:
                  >
                  >
                  > Scott,
                  >
                  > A dimmer type switch cannot handle the current full stop and is not
                  > designed to, what is required is a reostat type switch which will handle
                  > the currents involved due to the way it is constructed, (a varistat
                  > transformer could aslo be used intead) or what about a electric drill
                  > type motor or a flymo motor (electric hover mower) as these are a
                  > universal type motor in a lot of cases and will run on ac current so
                  > will take ac or dc type voltage and are easily controlled on ac or dc
                  > current, so as speed can be as well.
                  >
                  >
                  >
                  >
                  > --- In multimachine@yahoogroups.com, Darwin Wandler <wandler@> wrote:
                  > >
                  > > Rule of thumb start current instantaneous surge is 10 to 20 times
                  > rated
                  > > full load
                  > > run current. The reason breakers don't blow is they use a resistive
                  > > current detection
                  > > method which takes a few seconds to heat before tripping. Surge
                  > current
                  > > lasts for
                  > > less than 1 second in most cases. Fuses are instant blow so they can
                  > not
                  > > take
                  > > start current. You need motor fuses which are encased in
                  > silicon/ceramic
                  > > sand
                  > > to take the heat away on surge current yet blow on short circuit.
                  > >
                  > > Darwin
                  > > cvlac wrote:
                  > > >
                  > > > Hi Scot
                  > > > My motor is just a single phase 3hp one!
                  > > > Do you think that something can be made with this dimmer?
                  > > > Any way I need too a current delimiter for the start up of the motor
                  > > > because I have a 15 A fuse and seems that the motor absorbs more
                  > than
                  > > > that at start up .Any suggestion ?
                  > > > Costas
                  > > >
                  > > >
                  > >
                  >
                • Ash
                  ... discussion ... Charles, thank you for an excellent post, that probably took a while to write but it was certainly appreciated. Ash
                  Message 8 of 18 , Jan 11, 2008
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                    --- In multimachine@yahoogroups.com, "Charles R. Patton"
                    <charles.r.patton@...> wrote:
                    > There are a lot more ways of differentiating, but for this
                    discussion
                    > allow me some leeway.

                    Charles, thank you for an excellent post, that probably took a while
                    to write but it was certainly appreciated.

                    Ash
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