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60 Hertz Tolerance ??? ( Descriptive )

Discussion in 'Electronic Basics' started by Randy Gross, Nov 23, 2003.

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  1. Randy Gross

    Randy Gross Guest

    Following is a less candid approach to this question:

    I'm using a 1/10HP, 2800RPM, 12vdc, continuous duty motor to run a
    generator. I designed the rotor with a dual purpose: to mount the eight
    poles and, being a 9" diameter x 7/16" thick disk, act as a flywheel with
    the idea of relieving some of the burden placed on the motor. Properly
    balanced and cruising at 900RPM, I expect good performance.

    My problem lies in capturing the needed motor speed. I've considered using
    a belt drive with a 3 to 1 speed reduction but, that leaves 100RPM rampant.
    That will change the frequency to 66.7 hertz. I'm not sure that I can
    accurately reduce the speed mechanically, this is a new area for me.

    I want to keep this genny as close to fail-safe as I can, as few components
    as possible while achieving the desired output.

    an Inquiring Mind
    Randy Gross
     
  2. Ian Stirling

    Ian Stirling Guest

    What's wrong with simply using a sightly larger/smaller pulley?
    Say 3.33:1<
     
  3. Randy Gross

    Randy Gross Guest

    <Pd7wb.12099$9.net>...
    : > Following is a less candid approach to this question:

    <Snip>

    I'm not sure that I can
    : > accurately reduce the speed mechanically, this is a new area for me.
    : >
    :
    : What's wrong with simply using a sightly larger/smaller pulley?
    : Say 3.33:1<
    :
    Simply is what I am looking for. I looked for a source here in town but, no
    luck. I typed in pulley at google and it gave me sweaters (go figure). If
    you could simply point me to a source, I would be thankful.

    Randy
     
  4. Where's "in town" for you? Is there a Grainger outlet handy? (If not, they
    do mail order, I believe.) They'll certainly have what you need, though
    some of their stuff is pricey.
     
  5. I read in sci.electronics.design that Randy Gross <>
    Maybe you typed 'pully' in error. It's a twee abbreviation for
    'pullover', which is a sort of sweater.
     
  6. Zak

    Zak Guest

    Over here I think the keyword is 'belts'. Now, belts and pulleys have
    the same problem. Maybe V-belts?


    Thomas
     
  7. Randy Gross

    Randy Gross Guest

    "In Town" for me is Indianapolis, IN and the economy here is a mystery
    indeed. It seems all (almost) of the machine shops (auto industry related)
    are shutting down or are about to. They are not just downsizing to
    skeleton, they are in the grave, locked and assets auctioned. The question
    here is: Why is everyone jumping ship?

    <[email protected]>...
    : : > Simply is what I am looking for. I looked for a source here in town
    but,
    : no
    : > luck. I typed in pulley at google and it gave me sweaters (go figure).
    If
    : > you could simply point me to a source, I would be thankful.
    :
    : Where's "in town" for you? Is there a Grainger outlet handy? (If not,
    they
    : do mail order, I believe.) They'll certainly have what you need, though
    : some of their stuff is pricey.
    :
    :
    :
     
  8. Michael

    Michael Guest

    Why dont you just use an inverter?
     
  9. Big John

    Big John Guest

    Hi Randy,

    The exact speed of the DC motor will not normally be 2800 RPM. In a DC
    motor, the motor speed is close to being directly proportional to the
    voltage. So, even under the best of conditions your motor's speed will be
    no more accurate then your 12 volt DC source. The motor's speed will also
    vary with load. Even if you get a pulley that will give 60 Hz at 2800 RPM
    your speed will vary significantly with your source and load. Also note
    that motor ratings are nominal and in the case of a DC motor, you may not be
    at exactly 2800 RPM at exactly 12 Volts and a 1/10 Hp load.

    Having a flywheel is a good idea as it will help smooth out sudden changes
    in load, but you will still need some type of speed regulation system to
    stay close to 60 Hz.

    My advice would be to use the 3:1 pulley. Then sense speed on the
    alternator shaft using a tach generator, optical encoder, or whatever and
    have the speed regulator drop the motor speed as needed to hold 900 RPM for
    your alternator. The easiest way would be by having the speed regulator
    adjust the source voltage (I'm guessing that your DC motor is a PM type).

    I know that you said in your post that you want to keep it simple, but
    you'll need some type of speed regulator if you want an accurate alternator
    frequency. If you want an idea of where to start do a google search on "DC
    motor control" and "PID control".

    If you want more help both the group and I would need a bit more info on
    what you are trying to do, the frequency accuracy you need, what you are
    using for a 12 volt source (battery, lab supply, etc.), what type of DC
    motor you are using, and what type of load your alternator is going to see.

    Hope this helps,
    Big John

    --->>> Remove the nospam to reply to my email address <<<---
     
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