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Distressed Nerd - How to increase Motor RPM?

Discussion in 'Sensors and Actuators' started by Distressed Nerd, Dec 12, 2014.

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  1. Distressed Nerd

    Distressed Nerd

    Dec 11, 2014

    As an engineer who graduated #2 out of 10 in my class from a top tier university, yet I am completely, 100%, stumped on this electronics project and feeling like I a complete doo doo head and I am in dire need of help from my nerd comrades.

    What I am trying to do is increase the RPM’s of this fan motor. Right now it has a 4 setting selector switch (off, speed 1, speed 2, and speed 3), but I need more power or RPM’s then the highest speed setting (speed 3) will give me. A picture and all the details is attached, anyone who can solve this problem I will worship you! Just let me know the parts and wiring and I will turn your words into a finished project.

    If the rpm’s can not be increased using the motor I have now – then please let me know an easy motor setup I could install to give me more RPM’s then the current setup.

    Thanks a ton guys!

    Attached Files:

  2. Bluejets


    Oct 5, 2014
    Your photos , although showing details, are far too small to decipher.
    However, it appears to be a single phase AC cap start/run induction motor.

    Speed of these is fixed by frequency and by number of poles (windings) ....
    Only way to change speed otherwise is a variable frequency drive , but this was not designed for the purpose and will undoubtedly oveheat.
    Cost would not make it a viable option also.
    Only suggestion would be to get an interior cooling fan motor from a car wreckers.(DC...then vary the voltage)
    hevans1944 likes this.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I agree with @Bluejets solution: just buy a DC fan motor salvaged from an automobile wrecking yard and power it with an adjustable DC power supply. Nothing fancy required: just a step-down transformer, a Variac in the primary, a bridge rectifier in the secondary, and maybe a few thousand microfarads of capacitance for filtering. Might not even need the capacitors, as the inertia of the motor armature and inductance of the field-coil will provide some filtering. A series-wound DC motor will give you the maximum speed. You might have to rig up a pulley to your fan from the motor if speed isn't enough for direct fan drive from the motor shaft. Watch the RPMs so as not to exceed the capacity of the bearings!
    Russell368 and KrisBlueNZ like this.
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Variacs are big and expensive. I'd suggest an off-line switching power supply with adjustable output voltage. I agree with everything else though!
    hevans1944 likes this.
  5. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Yeah, I'll admit I am a fan-boy for variable autotransformers. I have collected a few over the years, both manual as well as stepper motor driven. Thinking about it, this proclivity for such things probably goes way back to my first Lionel train set, which used a variable autotransformer to control AC track voltage.

    Variacs® come in all sorts of sizes, but I don't understand why they are so expensive now that the patents have long since expired. I've always acquired them for personal use from discarded, usually obsolete, equipment. From time to time I will order one for lab use at work... little table-top units with a line cord, a 10 A fuse, a toggle on/off switch and a convenience outlet all built in... and I always wince at the cost. The scientists here use these (against my advice) to control the speed of little synchronous gear-motors mounted inside vacuum coating chambers to rotate coating samples in front of a sputter gun. I won't even go into why this sort of works. Obviously the synchronous motors are not turning synchronously with the line frequency when you starve their excitation by turning down the voltage. Can't argue with a PhD about it when it obviously works (sort of) for them. So, I just sigh and remind them to use an isolation transformer to avoid ionizing directly from the power line the residual gas in the vacuum chamber.

    Anyway, @KrisBlueNZ of course the OP should buy an inexpensive, variable-output, switch-mode DC power supply.

    But if they just happen to have a Variac® laying about with nothing to do...
    KrisBlueNZ likes this.
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Yeah I like variacs too. I guess the high price is just because they're a niche product nowadays.
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