Compound DC motor?

Discussion in 'General Electronics Chat' started by inwo, May 2, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Sold my parasail equipment today.:(

    Haven't used it in years. Time to let go before I hurt someone.:)

    Anyway, as I'm packing it up, I noticed the small armature terminal that I didn't use when I first built this.

    So long ago that I don't remember my thinking.

    Can someone explain if I'm correct guessing it's function?

    As I recall, it didn't seem to do much, no matter how it was connected.

    Motor is rated 225 amps @ 24 vdc.

    I only used it with 12 vdc. (as I recall)

    Is the small terminal marked "A" (middle of first picture) a third brush? I've never heard of that.

    If it wasn't marked "A", I'd suspect a parallel field winding. Used to prevent over speed.

    If the new owner asks, I'd like to have an answer.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Couldn't see anything marked so.
    It wouldn't be a brake at all would it?
    Max.
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Grounding brush?
     
  4. inwo

    Thread Starter Well-Known Member

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    There is an "A" next to the small unconnected terminal.

    Motor works fine without it connected.
    It came with an inadequate brake on opposite end.

    Can't remember how it was actuated. It released ok.
    Never understood why the brake wouldn't hold anywhere near rated motor torque. So I made a new one.

    The terminal is on the power input end. (By the brushes I believe)

    Military surplus, davit winch motor. Was never able to get more information on it. At the time I was more interested in the mechanical design of the project.

    Now I guess I'll never know.:( Not worth tearing it down just for curiosity sake.
     
  5. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Could be! Whats that?

    I could low ohm it tomorrow.
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Google winch motor. Apparently it is a standard format for reversing. Contains a solenoid and the A terminal has to be sorted to the more negative terminal... Yadda, yadda, yadda.

    You'll see when you google it up.
     
  7. inwo

    Thread Starter Well-Known Member

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    Can you get me a link?
    Nothing on the first 5 google pages.
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    Here is one of the many pics from the Google link. It seems to explain pretty well how the direction change comes about (pun intended)
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That would be a standard reversing of a series or compound wound motor, but inwo says it works without out it and it is a small terminal marked A.
    What about for an ammeter and is uses the field as a shunt?
    Max.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    A control Box is needed with solenoid. It will work in one direction without the control box.

    http://ecx.images-amazon.com/images/I/81p+EOp0alS.pdf

    Also google up WARN brand winches. There are a bunch of forums pointing to a test procedure, F1, F2 terminals and the A-terminal.

    Apparently it is a series wound motor and possible that it works in one direction and not the other for certain failure modes.
     
  11. MaxHeadRoom

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    Jul 18, 2013
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    I don't see any reference in any of the links to exactly what the function of the A terminals is?, in the PDF it just goes to supply negative with no other reference?
    Max.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I found a winch control box circuit earlier. I didn't take the time to understand it, i should have copied the link. Sorry. It think it was just a reference to keep the motor chassis at ground (neg battery terminal reference) on trucks, boats or other 12 or 24 volt circuits powering winches.

    If you don't find it, I will look again when I have time.
     
  13. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    All I saw was the standard series motors with both F terminals available for reversing.

    My motor is a series motor with only one terminal available. The other grounded.

    The extra terminal draws about 4 amps when connected high.

    Motor runs about the same with it connected high or low.

    As I'm only running motor unloaded on 1/2 voltage, any regulating effect may not be noticed.

    I question why it's not just connected internally.

    Max,
    Could be your first thought. Something to do with braking or brake release.

    As motor is not reversible, it would need a controlled method of lowering the load.

    I don't recall any brake connections. Seems it released with the motor running current.

    In that case it would need another release method for reverse.:confused:
     
  14. THE_RB

    AAC Fanatic!

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    A is normally for "Armature". BillB3857's schematic is for a reversable motor where the two field wires are reversed, and the main armature current is the A winding.

    In Inwo's motor the small "A" terminal might be for armature grounding, a grounding brush. Maybe to stop potential problems in winch motors that could be caused by the spooling of plastic rope etc building up static on the armature?

    If it is a grounding brush it just connects to the armature steel shaft, and will not produce any voltage at that terminal when the motor is spinning (except some noise).
     
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