Variable speed control

Discussion in 'The Projects Forum' started by billfromvt, Feb 7, 2015.

  1. billfromvt

    Thread Starter New Member

    Feb 7, 2015
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    Hi everyone,

    I have looked everywhere on the forum for an answer but may well have missed it, sorry if it has already been asked.

    I have a 240 volt water pump motor which has a max load of 370 watts. I have removed the water part and am just left with the motor. I've made a male thread on one end of the shaft to take a female coupling and this will hold the work I need the motor to do.

    I need the motor to run at variable speeds from 0 to 3000 rpm, I've thought of a light dimmer switch but I don't think it would be good enough, my other option would be the speed controller from an electric drill. I am open to other suggestions and ideas.

    Thanks in advance

    B
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you will not get 0 - 3000 range of speed control. likely to be a low end of 500-800 rpm's with any control scheme you use. AC induction motors are not on friendly terms with any voltage or freq changes. DC perm mag motors are a better choice for speed control in such a wide range
    0 rpm low end operation will be your biggest problem. torque will be very weak in most motors at those low speeds. I think AC repulsion motors can develope large torque at very low speeds.
     
    Last edited: Feb 7, 2015
  3. billfromvt

    Thread Starter New Member

    Feb 7, 2015
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    Thanks for the reply, I thought I was being a little optimistic in 0 - 3000 a good starting guide would be around 250, I just don't want it to spinn so fast at the initial start up that it breaks the product I am trying to spool
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Then an AC light dimmer circuit may work for you.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That could depend on the motor technology, the OP hasn't indicated what type yet.
    Max.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    True. I assumed the 240V water pump motor was induction.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If it is cap start/run, it may not like Triac control. They tend to drop out of run when rpm is lowered and under load.
    Especially when 0-3000 is needed.
    Max.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    The op just wants it to slow the initial start-up so a Triac controller my work for that.
     
  9. Duane P Wetick

    Active Member

    Apr 23, 2009
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    A variable frequency control (VFC) is usually used to control AC induction motors and is sized for the motor HP rating. In your case, that is 1/2 HP. Water pumps are usually most efficient when run at their full rated speed. Throttling the inlet stream or restricting the outlet stream are means of varying the flow while the pump is running at its most efficient speed; (nameplate RPM). Alternatively, you may want to connect the inlet and outlet ports with a bypass valve, thus regulating the flow while the pump is at its full rated speed. Its probably worth your while trying these methods.

    Cheers, DPW, Everything has limitations...and I hate limitations
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The OP specifically mentioned he has removed the motor from the pump, evidentally for other uses.;)
    Max.
     
  11. billfromvt

    Thread Starter New Member

    Feb 7, 2015
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    Good morning all and thank you for the great replies. It is an induction motor designed as a water pump but the water part has been removed just leaving the motor and the shaft exposed. I have tried a dimmer switch, that was my first thought but that just popped as soon as I put power to it. I am still thinking the electric drill speed control is probably the way to go. This is just a prototype, so I can try anything (Within reason) at this stage.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The drill controller is going to be a triac controller also, these are intended for Universal motors, which you maybe should be looking at instead of a induction motor, your results with one is as I predicted.
    1ph induction motors do not control well, they rely on running at close to synchronous frequency.
    In any event, you may be better off looking for a different type motor.;)
    Max.
     
  13. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    945
    I have experimented with the brushed universal motors found in cheap, upright vacuum cleaners.

    12-48 volts DC. That's DC now. DC

    I ran them with Lead acid batteries through an old auto-transformer I had wired as a Rheostat. They wanted to draw more than three amps at 24 volts and pulled about 2 amps on 12 volts.
    They have a surprising amount of torque, and develop it at zero RPM. If you can afford to source a decent sized(wattage), Rheostat, you could get 0-3000 rpm by running a universal brushed AC motor on DC battery power.
     
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