Doubling line frequency 50hz to 100hz

Discussion in 'The Projects Forum' started by shangrila, Nov 14, 2008.

  1. shangrila

    Thread Starter New Member

    Nov 14, 2008
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    Hi,
    I need to get 100hz @ 220volts out of 50hz (220 volts) normal household supply.
    Actually, for my mixer machine I have to double the rpm (2800) of 1hp induction motor to 5500 rpm. And, one of my friend told me that doubling the line frequency from 50hz to 100hz can do the job. I am heard of VFDs but these are expensive and overly sophisticated for the purpose.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Well, the best and most efficient way is to buy a commercial inverter to make your job. I dont suggest you to build one because it wont be very efficient and it will cost more than a commercial one.
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    A full wave bridge will give you double the frequency, but there's a lot of other harmonic stuff that may or may not be troublesome. It's certainly a cheap test!

    eric
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    A belt and pulley speed increaser will be less trouble than the VFD drive. Think about it after the full wave rectifier trial.
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    You cant use a bridge rectifier to drive an AC motor. The frequency doubles but the voltage is not AC anymore. If you do it you will destroy the motor.

    Beenthere is right about the pulley, maybe is the easiest solution but note that the output torque will half too.
     
  6. shangrila

    Thread Starter New Member

    Nov 14, 2008
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    Commercial inverters works with 50hz, so how i can change it to 100 hz. What i know is to rectify 220~ with bridge circuit, insert a capacitor filter but the rest of it is what i am seeking.
    Pully/gear is my last option as it will increase the weight and lead to machenical instability
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Are you sure your induction motor will work at 100 Hz? Or, will it overheat and/or give poor power? The VFD drives I have seen and used give a small amount of overspeed, but not two times for conventional motors. For 2X, I am with the others in recommending belting or gearing.
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    The rest you are seeking is the circuit of an inverter. With an inverter you can vary the frequency but i dont know how much you can increase it. Also, your motor may not be able to work at 100Hz and brake down, as jpanhalt said, and may parts inside the motor get destroyed to to centrifugal forces because the motor is not designed for this high speed. Its better to use pulleys to adjust the speed.
     
  9. onlyvinod56

    Active Member

    Oct 14, 2008
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    I think u may use a step up cyclo converter. Better use GTOs for the switches
     
  10. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    If you couple the output of the rectifier through a capacitor, it will be AC...sort of. :)

    Eric
     
  11. ad8bc

    New Member

    Oct 30, 2008
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    Believe it or not I have found ABB VFDs for cheap at hamfests and occasionally on eBay. There are a few on eBay right now but not knowing your motor HP specs I couldn't pick one out for you.

    it's good to know that VFDs generally don't output a sine wave, it's PWM at a particular (and sometimes adjustable) carrier frequency. VFDs are called inverters because they convert the line-side voltage to DC and then re-invert the DC into whatever frequency is needed.
     
  12. shangrila

    Thread Starter New Member

    Nov 14, 2008
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    0
    thanks,

    I think 555timer (for GTOs) with 50% duty cycle would be fine, as GTOs need continous gate current to remain open ... am i right? or something else could be used for timing.
     
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