Distressed Nerd - How to increase Motor RPM

Discussion in 'The Projects Forum' started by Distressed Nerd, Dec 11, 2014.

  1. Distressed Nerd

    Thread Starter New Member

    Dec 11, 2014
    5
    0
    Hello!

    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!
     
  2. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    As far as I can tell, you're boned. HP required goes up by RPM cubed. That fan blade is matched to that motor and it (the motor) will smoke if you can even get it to go faster.

    You will exceed its amp rating in only a few dozen RPM.

    At least I gave you the math to determine the HP required if you DO buy a faster motor.
     
  3. JWHassler

    Member

    Sep 25, 2013
    201
    33
    What #12 said.
    Fans are not usually designed with hidden capabilities, and usually, the lower-speed settings are crippled versions of its top speed.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,173
    1,797
    What makes you think it is possible to raise the RPM with your current setup, which looks like a synchronous AC motor with 3 pole pairs. Three speeds is what you get.
    http://en.wikipedia.org/wiki/Adjustable-speed_drive

    A multi pole brushless DC motor, as used in a disc drive, can be run at much higher RPM. Of course you don't want the blade tips to go supersonic, and noise increases as the 7th power of the tip speed.
     
    #12 likes this.
  5. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    True. Medium and Low are just longer windings attached in series with the High winding. They create more impedance and that reduces current which slows down the motor.
     
  6. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Well, that looks like a disagreement between me and Papabravo. I'm only talking about the motors I am familiar with, and "cheap fan motors" seems to fit this description.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,061
    Running a motor beyond its rated rpm is a bad idea, even if there is a way to do it. I'd look for a different motor.

    Wow, I really got outgunned on this one. I thought I was responding to #1.
     
  8. Papabravo

    Expert

    Feb 24, 2006
    10,173
    1,797
    Lotta knowledgeable folks heah, un,,huh!
     
  9. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    There's one I didn't know!
     
    wayneh likes this.
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,567
    2,379
    Appears to me as a split phase induction motor, if so the rpm is governed by the frequency of the supply and the switched-in pole count.
    2-pole = maximum rpm.
    Max.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,567
    2,379
    See fig 2-52 2-53.
    Max.
     
  12. Distressed Nerd

    Thread Starter New Member

    Dec 11, 2014
    5
    0
    Thank you for the responses this forum is a gem!

    The actual fan is shown here to get an idea of what we are looking at: http://www.laskoproducts.com/max-performance-pivoting-utility-fan-model-u15701/

    From my understanding the current setup would require some complicated wiring, if even possible to increase the RPM's, and the best route would be to go with a DC motor. From my understanding DC motors are easier to adjust RPM's, since we can directly control power with potentiometer or variable resistor?

    What I don't know exactly how many RPM's the current motor is spinning at (but from googling it looks to be in the 800 - 2000 rpm range. Any recommendations as to the DC motor setup I should go with?

    You guy's are electrical wizards, I am taking notes furiously!
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,567
    2,379
    You would require a DC supply for a DC motor, it may be possible to look at a Universal motor, these run off of AC and can be controlled by a simple Triac controller if needed.
    You would have to watch the rpm's however as a Universal motor operates in a runaway condition for a particular voltage, used in power tools and vacuum cleaners etc.
    That fan appears to be a squirrel cage fan?
    Max.
     
  14. Distressed Nerd

    Thread Starter New Member

    Dec 11, 2014
    5
    0
    Thank you Max. Yes the fan it is a squirrel cage fan - the motor currently installed is almost completely silent I would need something similar so I could isolate the noise being generated by the fan blades spinning. What specs would I need to be looking at to determine how loud the motor would be? My power tools and my vacuum cleaner is very loud which both have a lot more torque/hp required, so maybe I would need to look for motors with low hp/torque but high RPM's?

    Any resources for purchasing motor setups you could point me toward would be much appreciated.
     
  15. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Hp is torque times something RPM. That particular question is therefore not proper.
    Go with RPM2/RPM1 = (HP2/HP1) cubed.

    Next: Does that fan run with the tips aimed at the outlet or slanted back away from the outlet?
    If they slant backwards, it is an "unloading" fan blade and you will only make a bigger whizzing noise if you run it faster.
     
  16. Distressed Nerd

    Thread Starter New Member

    Dec 11, 2014
    5
    0

    The motor is 1.1 Amps to get that to Watts (or horsepower) I need to know if it is Three phase or Single Phase (see: http://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.htm) - did we decide?

    The tips are aimed at the outlet aka "forward curved blade" centrifugal fan (see: http://en.wikipedia.org/wiki/Centrifugal_fan), so if I increase RPM's I will get higher pressure and more air flow - Right now the 3 speed settings gives me an increase in pressure & outflow from speed 1 to speed 2 to speed 3. I did not know "backward curved blades" only increase sound, but don't do much to increase air flow. I guess that explains why leaf blowers only have 1 (rarely 2) speed settings

    #12 You are da bomb you're like a Google/Siri/Cortana of the 23nd century.
     
  17. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    See post #8

    I'm not anywhere near the best on this site. I'm just the only one that does fans for my day job.

    ps, it only has 2 power wires so it must be single phase? (I'm not all that good with motors.)
     
  18. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Your drawings are what I usually see, just more windings for slower speeds. The schematics give me no clue that the number of active poles are being changed to get different speeds. Maybe I should have gone to school that day. :(
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,567
    2,379
    The present one is Single phase.
    Depends what your budget is, if you really wanted to spend you could swap the motor with a small 240v 3ph motor and control it with one of the 120v (or 240v) 1ph input VFD's (variable frequency drive), both versions put out 240v 3 phase and can be set for continuously variable or 6 -8 pre-set speeds.
    A standard 2 pole motor can be increased up to around 80 - 100Hz.
    85Hz would give you 5000rpm.
    Max.
     
  20. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Now, that's a motor guy. I just do fans.:p
     
Loading...