dc motor does not reverse

Discussion in 'General Electronics Chat' started by rshwin, Aug 7, 2008.

  1. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    I am using an old (marine) starter motor in a project in which I need it to go forward and in reverse. However when I reverse the polarity it does not reverse. I am using a battery charger for the power source currently, does that make a difference. What could I do to make it go in reverse???
     
  2. gotumal

    Active Member

    Mar 24, 2008
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    What is the current rating of that charger. Does it match with motor? Are you using a H bridge or eaperimenting directly with the battery charger?
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It is series wound and not easily reversible most likely. They can be reversed, but it requires getting access to the field coils.

    John
     
  4. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    Yes everything eems to be wired in series. Should I wire the brushes and feild coils in paralell?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    No, because then the motor would not work properly.

    If you wish to reverse the direction of the motor, you will either have to swap the polarity of the brushes OR the field windings - not both at the same time.

    The fact that the starter motors of positive grounded autos had field windings made them a snap to convert to negative ground. The fact that they had generators rather than alternators helped quite a bit too.

    There wasn't much hope for the radios though.
     
  6. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    See "motor stuff" pictures at this link. Motor2 is the original wiring for the motor. I have tried the following wirings of Motor3 through Motor6 and none work. What am I doing wrong? How can I wire this motor to go in forward and then reverse? Any help Please!!!!!
    http://rshwin.spaces.live.com/
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Are you using the original pinion drive gear that came with the motor? Those are usually set up so that they free-wheel in the reverse direction to prevent damage when the engine starts.
     
  8. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    No I ground it down to a smooth .5" shaft for a pully. This darn thing only seems to run in its originall wiring config. Every other wiring of it causes the coils to energize and not move. It'd be a good electro magnetic brake though. Any ideas.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    For starters, I have never reversed a series wound motor. So this comment is based on what I have read and understand. No guarantees.

    1) I assume the connections to the brushes are essentially fixed. That is, you cannot easily disconnect the grounded brush(s) from the motor case.

    2) To reverse the motor, you need to reverse either the field relative to the brushes or the brushes relative to the field, but not both. So, reverse the field only. It must go through the brushes (as shown in your picture #2 of the original) and not go directly to the other power pole (e.g., ground) as shown in your picture #3.

    Attached is a drawing of what I mean.
    View attachment 4156


    I hope it is clear. John
     
  10. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    Ah ha eureka! ...Kinda
    I have got it to run in both forward and reverse but at a tremendous amperage drain and with high heat. So Jpanhalt is that because I have grounded the lead from the field coils, and ran the brushes on a seperate circuit (see the link - "Motor Stuff" at the link "Motor8")?
    I thought maybe the high amp draw was through the brushes - so I put in new ones. Then I thought it was just bad connections so I re-soldered. Then I tested the commutator plates and being not to familiar with motors I found what to myself seems to be questionable- that being that when testing continuity between commutator plate contacts I get zero ohms between all commutator contacts. Is that how it should be? I assumed that since the brushes are at 180 degrees, that only the commutator contacts 180 apart should have continuity, or am I wrong?

    Also, If it is because I am connecting the feild coils series to ground and running the brushes in paralell, that I am getting an extreme amp drain, heat and power loss is there any other way to limit the amp draw, say through a resistor between feild coils and ground?

    So that's 3 questions:
    1. feild coils to ground, and brush circuit in paralell - high amps/heat
    2. Commutator continuity (zero ohms) between all contacts.
    3. Installing a current limiter between feild coils and ground, if that is the problem.

    Please do help greatly thankful.
    http://rshwin.spaces.live.com/
     
    Last edited: Aug 18, 2008
  11. rshwin

    Thread Starter New Member

    Aug 7, 2008
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    Jpanhalt
    Never mind all Jpanhalt's diagram fixed all the problems. My motor quandry/conundrum
    is at an end. Thanks to all who have taken the time to answer my -what must seem quite basic questions.

    Thanks!!!:):)
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Great that you got it working :)

    Keep in mind that starter motors were not designed for continuous duty. I suggest that 30 seconds of operation followed by a 120 second cool-down period will keep temperatures within reason.
     
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