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Help on wiring up separately excited Dc motor with 4 wires not 2 ?

Discussion in 'Electronic Basics' started by Rob, Jun 2, 2005.

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  1. Rob

    Rob Guest

    Hi
    hope some one can help me with this problem i have ....i just won on
    ebay a 24 v dc Nelco motor with wound field and armature type
    separately excited ?..when i tried to connect it to my 24 v battery
    there are 4 connections? where do i put my positive and negative
    terminals?..

    thanks

    Robert l
     
  2. Chris

    Chris Guest

    Hi, Rob. You haven't given us a lot to work with here. So I guess
    you'll have to do some detective work yourself...

    Based on the assumption that you've got a motor with 24VDC armature and
    24VDC field, you should get your ohmmeter out (with the motor not
    connected, of course). By checking for continuity between all the
    wires, you should find two pairs where there's a fairly low resistance
    between.

    (The following advice only applies if that is true.)

    Of those two pairs, it's a safe bet the one with the higher resistance
    is the field. The lower resistance pair should be the armature. Also,
    if there's no gearing, you should be able to manually turn the motor
    shaft. You will find that the armature resistance will "blip" as the
    brushes commute, whereas the field resistance will basically stay the
    same.

    Many times, the armature on DC motors made on this side of the pond
    will be red (+) and black (-). Euro/Brit motors are more likely to
    have brown (+) and blue (-) as the armature, but don't bet the farm or
    the motor on it.

    Remember, the field usually gets the fixed voltage, and the armature
    gets the variable voltage to control motor speed.

    Trust, but verify. Start things up with a current-limited power supply
    and try "bumping" it, providing voltage to armature and field for half
    a second. That should give you a clue if things are wired correctly.

    And by the way, sorry for the sketchy answer. More information usually
    results in a better response on s.e.b.

    Good luck
    Chris
     
  3. Bob Eldred

    Bob Eldred Guest

    Just adding to the above post, you should determine if the motor is series
    or shunt wound. If it is shunt wound, the field will connect to the 24 volt
    source in parallel with the armature. If it is series wound the field
    connects in series with the armature. A shunt field will have a high
    resistance winding, a hundred or more ohms and will draw a moderate current
    on 24 volts. A series field will have a low resistance of a few ohms or so.
    The armature will always be a low resistance of several ohms and will change
    somewhat when the motor is manually turned as was mentioned. So, if there is
    a high reistance winding, connect it in parallel with the other, low
    reistance winding. If there are two low resitance windings, connect them in
    series. It will not matter which wire of each pair hooks to which wire of
    the other pair as this only determines the direction of rotation. To reverse
    the rotation, reverse one pair, either the field or the armature but not
    both. The polarity of the battery will not matter.
    Bob
     
  4. Rob

    Rob Guest

    Thanks for the help Chris and Bob i have asked for help from the
    seller of the motor but he doesnt know :(

    http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=7514227421&rd=1&sspagename=STRK:MEWA:IT&rd=1

    the above link describes the motor..

    I will use your advice tommorrow...Even after i figure out how to wire
    it up .. will i need to use 2 seperate 24 v supplies for each
    winding?.. I know nothing about motors..I have took the top cover off
    the motor and inside there are 4 capacitors(each one conected in
    pairs)..all wires are black and are of the same thickness..I tried
    this morning to wire 24 v to the top 2 connectuons and another 24 v on
    the lower two connections..i got a few big blue sparks so
    stopped...motor did not turn...

    I also did this experiment... i connected a electric drill chuck to
    the motor spindle and set the drill going... then using a multimeter
    tried to measure the voltage... thinking that i could pinpoint the
    correct terminals...but the voltage was very irractic..so i stopped
    that as well ...
     
  5. Don Kelly

    Don Kelly Guest

    One supply should do. However the key thing is -is it series or shunt wound?
    The "capacitors" are a puzzlement -unless they are for RF suppression. Are
    they actually capacitors?
    A shunt wound motor will have, as you have been told, a high resistance in
    the field winding. In that case wire the field in parallel with the
    armature. If rotation is wrong, reverse either field or armature leads.
    If the field is seiries, it will have a resistance which is low, of the
    order of the armature resistance. Which is which is not a problem as you
    connect them in series. If rotation is wrong, reverse as above. Note that
    the no load speed can be very high so you should have a load on the shaft at
    all times.
    What is the name plate data and have you checked with the manufacturer's
    site regarding this particular model?
     
  6. Bob Eldred

    Bob Eldred Guest

    This is pretty healthy motor, 400 Watts so expect it to draw about 17 Amps
    from the power supply or battery when under full load. Stall current will be
    higher than this, maybe as much as 100 Amps depending on the mechanical
    load. It will draw the stall current as it starts from a dead stop.
    Therefore, you'll need a beefy power supply. Based on what you said above,
    you may not have enough current to get it moving.

    Before you hook any power to it, measure the windings with an ohmmeter to
    determine if it is series or shunt and to determine which wires are paired.
    Since the name plate speed is listed as 1600 RPM, I suspect that this is a
    shunt wound motor. Series motors do not have a well defined speed and the
    RPM is usually much higher.

    The resistances will be lower that my estimates in the above post because
    its a bigger motor than I thought. A shunt field may be only 10 or 20 Ohms
    and the armature will appear as nearly zero ohms, maybe a few tenths of an
    ohm. A series field would be less than an ohm also.

    You may use one or two power supplies, it doesn't matter. The field supply
    can be smaller, several amps and does not need to supply high start
    currents. The armature supply will need to supply a fair amount of current
    to get the motor turning. With no mechanical load it might be 10 amps or
    more. You can use variable voltage supplies to vary the motor speed but be
    careful in changing the field voltage. This works backwards from the way you
    might think A lower field current speeds the motor up and a disconnected
    field may cause the motor to run away and over speed. Be sure you can switch
    everything off quickly should anything go wrong. Good luck.
    Bob
     
  7. colin

    colin Guest

    try wiring the windings up in series, it should at least turn this way even
    if its meant for parallel operation, if the wires are the same size then i
    would be pretty syure its meant for series anyway, might be best to use 12
    volt car battery (with care as the gases they produce under heavy fualt
    conditions can explode etc), but first are you positive its a dc motor, oh
    wait i asume it says this on the plate.

    Colin =^.^=
     
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