DC Motor Wiring Problem

Discussion in 'The Projects Forum' started by abbefaria, Nov 28, 2012.

  1. abbefaria

    Thread Starter New Member

    Nov 20, 2011
    3
    0
    Let me preface this by saying that I know very little practical stuff about hooking up motors. I'm a final year undergraduate EE student, and although I'm pretty good with motor theory, working with actual motors is very different.

    What I have is a Fasco 24V, 4.94A DC sealed ball bearing motor (Model 7104-0424, type 04). I cannot find any documentation, from the manufacturer or otherwise, online. Out the back are two wires, black and red, and then welded to the side is a small metal box with a variable control knob on its face. This box has a green wire coming from it. I know this motor is probably too small to worry about starting circuits. I have a DC power supply that was used previously to run this motor, but I have no knowledge of how it was hooked up and have no way to find out, either, which is unfortunate.

    I have tried the following wiring combinations, in the order listed. I was careful to bring the voltage up from zero to 24V slowly, which I hoped would help avoid any burn-out in starting or blown fuses (don't know if this helps or not...).

    • Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> float
    • Red Wire -> Negative Terminal, Black Wire -> Positive Terminal, Green Wire -> float
    • Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Power Supply Chassis Ground
    • Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Negative Terminal
    • Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Positive Terminal

    Under all of these conditions, the motor does not run and draws no current. I have checked the power supply, and it is working fine. The connection diagram on the motor's faceplate says only "red --- + supply, black --- - return". There is no mention of the knob and green wire, and the internet is surprisingly silent on my problem. If any of you have any insights, I would really, really appreciate it! Thanks very much for any input.
     
  2. williamj

    Active Member

    Sep 3, 2009
    180
    32
    abbefaria,

    I am also unfamiliar with this motor. But I do have a question. Have you checked continuity?

    (black to red, black to green, red to green, black to case. red to case, green to case)

    Good continuity between black and red would indicate (to me) a good coil, good continuity between green and case would indicate a chassis ground, other continuity might indicate the purpose of the green wire or a short or open circuit.

    williamj
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    I would open the box up and look inside to see what its doing, also what resistances are you getting between these three wires?
     
  4. abbefaria

    Thread Starter New Member

    Nov 20, 2011
    3
    0
    Thank you all for your help. I did a continuity check - the fuses were good, and it turns out the green wire is electrically connected to the motor chassis. I put in a call to Fasco, and the wires are supposed to be connected as Red->Positive, Black->Negative, Green->earth or chassis ground. I had already connected them up this way, so the rep suggested that the terminations are at fault. I cut off and re-terminated all of the wires with new connectors, and voila! I guess something must have happened with the old connectors. In any case, it works great! Thanks again for the assistance.
     
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