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DC Motor. Which Type?

Discussion in 'Electronic Design' started by Ira Rubinson, Jun 21, 2007.

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  1. Ira Rubinson

    Ira Rubinson Guest

    I have a 90VDC motor with no tag. The motor is attached to a gear box. The
    motor has 5 wires. 3 of these wires are 18AWG and one of the 18AWG is green
    ground. I can operate the motor by applying 90VDC to the other 2 18AWG wires
    and can reverse the rotation by changing polarity on these 2 18AWG wires.
    There are 2 22AWG wires that are not being used. The motor is used in a low
    horse power application for long time periods. Is there a way that I can
    determine whether this motor is:

    1. Permanent magnet

    2. Series wound

    3. Shunt wound.



    Are shunt connections typically smaller wires than those used to connect to
    the armature?



    Thanks -Ira
     
  2. MooseFET

    MooseFET Guest

    If it goes the other way with you excange the leads it is a PM motor.
    The exceptions are that it go "clunk" before it starts turning or it
    draws a huge current and goes very fast even on 12V.


    Yes, but it is unlikely to be the use of those wires.
     
  3. I suspect the 22 gauge wires are either connections to an
    over temperature switch intended to be used in an interlock
    circuit, or a tach generator output for speed feedback.
    Runs with only two connections, has speed roughly inverse to
    load torque.
    can have only two external connections, but speed varies
    much more than inversely proportional to torque. In other
    words has very high no load speed. If the nameplate has a
    speed rating, it is probably not universal (series) wound.
    Also, runs almost equally well on AC or DC. This also means
    that it turns only one way, regardless of polarity, so you
    have ruled this out.
    Normally has 4 wires exiting the motor, so the shunt supply
    can be adjusted separately from the variable armature
    voltage (when used as variable speed motor). Also has a
    speed roughly inverse to torque load. If internally
    parallel connected, and intended for only full voltage
    operation, it will turn the same way, regardless of which
    way you connect the DC. So your test already rules this out.

    You have a PM motor.
    For large motors, yes. But there is usually a minimum size
    wire used for voltage rating, even if it is not needed for
    ampacity.
     
  4. default

    default Guest

    Permanent magnet DC motors are frequently 90 VDC so it probably is a
    PM motor. (and you only have two leads to make it go . . . it
    wouldn't turn at all if the field needed excitation or would turn
    slowly)

    They see a lot of applications in exercise treadmills - but are also
    widely used in industry due to the very inexpensive controllers they
    require and single phase power.

    PM motors reverse direction when the power is reversed.

    Measure the resistance between the 22 AWG wires - likely to be a
    temperature sensing thermistor or over temp switch. Probably not a
    winding.
     
  5. Jamie

    Jamie Guest

    if you had a shunt motor, it wouldn't be turning. And thus, this leaves
    you with a universal type how ever, you did say that when
    reversing the wires the motor changed direction? so in this case, it
    would have to be a PM motor.
     
  6. Guest

    I deal with motors like that all the time. One application
    which all electronic geeks and college students can
    appreciate is the use of that type motor for the conveyor
    belt inside a pizza oven. The two smallest leads for the
    conveyor motors come from a magnetic pickup coil that
    picks up a pulse from a wheel shaped ceramic magnet
    on the end of the motor shaft. The pulsating output of the
    pickup coil is fed to the motor drive for the purpose of
    speed control ie cook time. The next time you visit your
    favorite mass production pizza place, ask someone if you
    may look at the drive unit for the oven belt. This same type
    motor is also used in automatic doors for grocery stores
    and hospitals.

    [8~{} Uncle Monster
     
  7. Rich Grise

    Rich Grise Guest

    So, in a few words, they might be tach leads, right? :)

    Now that I've nosed into the thread, I once saw a 90VDC 5 hp =:-O
    permanent-magnet motor. It was about the size of 1 1/2 loaves of
    bread on end.

    Just by inspection, a PM motor won't have visible laminations on
    the outside - wound-field motors usually do.

    I wonder what happened to the motor's nameplate?

    Thanks,
    Rich

    Cheers!
    Rich
     
  8. Just a note, since the above could be read as series wound are only
    built with 2 connections. Series motor come in at least 2,3,4,5 or 6
    connection variations. 2 or 4 are by far the most popular though.

    I do agree this is mostly likely a PM motor though.

    Robert
     
  9. Jamie

    Jamie Guest

    I think maybe the op may have been thinking of a universal motor?

    We have Series would shunt motors that we deal with, and those
    do change direction when reversing. the series winding helps some
    times but does not always need to be used!
     
  10. Could be, but hydralic pump motors often use the same type of wiring.
    They just aren't normally run on AC.
    That sounds more like a compound motor. With both series and shunt
    wound fields. The series field acting to strengthen (or weaken) the
    field created by the shunt wiring. There are many true series wound
    motors with more than 2 terminals. And, of course, those do change
    directions unlike the 2 terminal motors.

    Robert
     
  11. Last week I was trying to find some information on
    Starter-Generators, aka Dynastart or Dynastarters.

    These are often used on aircraft as 28V engine
    starters, and then battery chargers. They have a
    series field and a shunt field.

    On the face of it they look like a compound
    motor/generator. But things are not as they seem.

    It is a series-wound motor for starting, but a
    series-wound motor does not generate any voltage
    when spun in the direction of motoring. So, in
    order to generate an output voltage, the shunt
    winding then has to be energised to produce the
    correct polarity magnetic field .

    The thing that is confusing (to me) is that any
    output current also goes through the series winding,
    in a direction that reduces the field generated by
    the shunt winding. The Ampere-Turns in the shunt
    winding must be very large to overcome the series
    field.

    There is also the possible problem that the adverse
    compounding requires quite a lot from the voltage
    regulator circuit.

    Does anyone have experience of Starter-Generators?
     
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