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Hooking up a motor, wiring

Discussion in 'Electronic Basics' started by MikeC, Jan 18, 2008.

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  1. MikeC

    MikeC Guest

    Hi all,
    I know very little to nothing about motors. I am looking to get a
    motor to help improve my grain mill (I'm a homebrewer).

    What I know I need is this:
    1750 rpm

    I'll be running shome sheaves to tone that down to about 185 rpm. The
    specs I've read used a 1/3 HP motor. If i understand it right, slowing
    the rpms will increase torque. I'm not sure how much lee way I have
    with the HP, I need enough torque to crush the barley without making
    it flour.

    In the plans to plug this thing into a wall receptical, I'd assume I
    want 120V. I would think you can wire a 230V to plug into a 110V (or
    is it 120V) wall outlet. I've seen all kinds of voltage from 90 to
    above 240. What range should I look in for plugging into the wall?
    What about Hz, I know what the measurement of Hz is, but have no idea
    how it relates to motors? What the heck is a 2-phase or 3-phase motor?
    Should that mean anything to me? What about AC vs DC? I'd assume I
    want an AC motor, but could I wire a DC to plug into the wall?

  2. Guest

    if it 3 phase your home power will not work, thats big power and you
    do not want to mess with that it's a killer, you cannot plug a 230v
    into a 120 not enough power you will burn up your moter, you need to
    know excact power neede dfor the moter, did the mortor come with a
    plug? if it did dose it look like a regular plug? your best thing is
    to get a electrition, to wire it up for you so you dont burn somthing
    up like your motor or evan your house
  3. Tim Wescott

    Tim Wescott Guest

    Oy. You have a learning curve ahead of you. Please don't come crying to
    me if you accidentally grind up your hand.

    Gearing down the motor with belts or whatnot will, indeed increase torque
    as the speed goes down. You don't lose all that much power when you gear
    down, and power = speed * torque, so less speed = more torque.

    To plug it into the wall, you need a single phase AC motor. If you are
    currently turning the crank by hand you're probably doing about 1/20 to
    1/5 (if you're Conan) horsepower. If you run the mill at the same speed
    as you're hand cranking it you could probably get away with an even
    smaller motor, should you be able to find one.

    Tim Wescott
    Control systems and communications consulting

    Need to learn how to apply control theory in your embedded system?
    "Applied Control Theory for Embedded Systems" by Tim Wescott
  4. Dan Coby

    Dan Coby Guest

    That is a typical speed for a 4 pole AC induction motor running off of 60 hz.
    A 2 pole AC induction motor typically runs about twice that speed.
    Based upon this info, most of the remaining discussion will be focused
    on AC induction motors.

    "shome sheaves" ??? That is a new term to me.

    In general, with gears, reducing speed will increase the torque.

    Sorry, I have no idea about the requirements for crushing barley.

    That depends upon where you are located. In the US, a wall outlet supplies
    120 V at 60 Hz. In Europe, 240 V at 50 Hz is common (or so I have read).

    You probably want to select a motor with whose voltage and frequency match
    what you have available at your location. Some motors can be wired to
    operate using either 240 or 120 volts. Warning: You should not try to use
    a 120 V motor on 240 V. Likewise there can be problems running a 60 Hz
    motor on 50Hz.

    The speed of an AC induction motor depends upon the input frequency and
    the number of poles inside the motor. From your desired speed of 1750 rpm,
    this implies that you will want a 4 pole motor powered by 60 Hz. A 4 pole
    motor will run at about 1450 rpm if you run it off of 50 Hz. A 2 pole motor
    running on 60 Hz will typically run about 3500 rpm.

    There are variable speed motor controllers that you can buy that will supply
    a variable frequency to drive a motor at different speeds.
    In your power range (1/3 HP), a single phase motor is probably what you
    want. A 3 phase motor is typically used for higher power applications.
    A 3 phase motor requires 3 phase power. That can be a problem in the
    US since most homes are not provided with 3 phase power.

    There are several different types (and subtypes) of motors. They each
    have their advantages and disadvantages. The right type depends upon
    thing like the need for: constant speed?, variable speed? constant torque?
    variable torque?, power?, size?, reliability?, cost, etc.

    More information about motors can be found on the web. For example:
  5. me

    me Guest

    A good place to start is an old washing machine. They typically have a
    1/2 HP motor that runs about 1725 rpm you can also drill out the welds
    and get the motor mount with it...
  6. Tom Biasi

    Tom Biasi Guest

    Go to Rec.Crafts.Brewing.
    You will get plenty of help with your grain mill.

  7. MikeC

    MikeC Guest

    Sheaves are pulleys, one 1.5" and one 10". I am after constant speed.
    My mill should run at 185 - 200 rpm and not any higher. I do not want
    any big fluctuations in the rpm's.
  8. Jamie

    Jamie Guest

    to determine the HP (horse power) needed, you need a strain gauge to
    meter the load..
    A fish scale or something like that can give you a ball park figure
    if you don't have a real kit to work with.
    It's been a while since I have done this, I usually refer to a hand
    book for this but this seems to pop to mind..

    HP = 6.28 x RPMs x Foot-Lbs-at-one-RPM /33,000

    basically the foot lbs is the tension you get when moving
    the load for a full rotation at the rate of 1 minute.

    I guess you can start there to determine the HP.
    You would most likely need a single phase motor.
  9. Wim Lewis

    Wim Lewis Guest

    It sounds like you want a run-of-the-mill induction motor. They
    have a "natural" speed (their synchronous speed) and they slow down
    a little under load, but not a whole lot, unless they stall of
    course. They're also one of the most common kinds of 1-HP-or-less
    AC electric motor and they're cheap and reliable.

    Your mention of a 1750-RPM motor reinforces this: that's almost
    certainly a motor with a natural synchronous speed of 1800 RPM (60 Hz power,
    times 60 seconds-per-minute, divided by 2 because of the construction
    of the motor) which slows to around 1750 RPM under load.

    (The other really common kind of motor in that size is the universal
    motor, which can run off AC or DC (hence the name); they slow down more
    under load but they have plenty of torque even when stalled (unlike an
    induction motor). Universal motors are the kind found in hand drills
    and circular saws and such. But a universal motor doesn't have a natural
    speed; it just runs as fast as it can.)

    Induction motors are always AC, since they use the alternating-ness :)
    of the current to set up a rotating magnetic field, which is
    what drags the rotor around. Some devices can take either AC or DC,
    but in general, don't feed AC to something expecting DC (or vice
    versa): you'll burn something out.

    You don't need a 3-phase motor. Those are generally for larger
    industrial stuff. And you probably don't have 3-phase AC power available
    anyway. In the US, your typical wall plug provides 115 V (more or less)
    single-phase AC power, 60 Hz (exactly), and can provide at most 15-20 amps.

    Don't worry about getting the horsepower exactly right. A more powerful
    induction motor will still turn at its natural speed, it'll just have
    more force available to mangle your fingers if they get caught in the
    belt. An undersized induction motor will stall more easily.

    There are a few sub-types of induction motor, having to do with how
    they start up: split-phase, capacitor-start, and shaded-pole. I think
    you don't want a shaded-pole motor. Either of the other two sorts should
    work fine, but a split-phase motor is probably slightly cheaper and
    maybe simpler (capacitor-start motors have more starting torque,
    but I don't think you'd need that for a mill).

    Finally, I recommend you put a circuit breaker in between the motor
    and the plug (unless the motor has one built in), since electric
    motors can draw a ton of current when they stall, and can quickly
    overheat and burn out. You can look on the motor's nameplate to
    figure out what amperage the circuit breaker should have. I'd
    probably wire it up like this:

    wall plug >---- box with switch and circuit breaker >---- motor and mill

    (While writing this I found ths web page which will help you
    interpret the stuff printed on a motor's nameplate: )

    Another place to ask would be woodworking and metalworking craft groups.
    People are always putting new/different motors into their shop tools
    and I think the FAQs for those groups will include a lot of the same
    kind of questions and concerns you have.
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