Can anyone help with how to wire a small 12V DC wiper motor? (not PM!)....

Discussion in 'General Electronics Chat' started by tcolit, Aug 5, 2010.

  1. tcolit

    Thread Starter New Member

    Aug 4, 2010
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    Hi
    I am restoring a 1960s Mercedes and recently had a burned out windshield wiper motor rewound that has two speeds to the wiper motor. Unfortunately, they pulled things apart in such a way that they could no longer figure out how the internal motor wires (brushes, stator coils, neutral switch) were connected.

    I have been trying to figure out, using my own logic and trial and error, how to get the motor to operate at two different speeds in the same direction.

    In trying to understand the motor, I now have one of the brushes grounded to the motor housing, the other goes to one of the terminals that receives 12V DC outside the motor housing. Amazingly the motor already runs, with just that 12V power and the negative battery terminal connected to the housing and with only one of the stator coil wires that come from each end of the two stator coils connected to the positive side of the brushes (the stator is made up of two coils on either side of the motor). When I connect the second stator coil to the grounded brush, the motor runs in the reverse direction. I guess I could understand that the motor could possibly run with just one of the stator coils creating a magnetic field, but I'd like to know whether the two stator coils should be hooked up in series, parallel or how? And how do I achieve the two speeds? (I am certain that the motor is supposed to switch to a lower speed by applying 12V to a second one of the 12V terminals (through he external wiper relay), at the same time as the 12V for the high speed....

    Does anyone have any ideas how this could/ should be wired? I can provide more detail or clarification if someone thinks they have the answer or know what I could do. I am pretty desperate for help at this point and have many different wire connections that have yielded different rotation directions (and possibly power), but not a real difference in speed...:confused:


    Thanks a lot, Tom
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    How many wires come from the car side of the connector? Some times, the speed control is part of the car and not the motor. If it is only one wire, not including a possible ground wire, the speed control is in the car. If there are two wires, again not including a possible ground wire, the motor itself is a two speed. A drawing of what wires are available from both the car and motor would be most helpful in solving your problem.
     
  3. tcolit

    Thread Starter New Member

    Aug 4, 2010
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    Hi Bill

    To clarify. The speed control does come from the car, in a way. To achieve the low speed a second 12V is applied to a separate terminal on the motor. In total there is one ground terminal (the housing and three 12V terminal outside the motor. One always has 12V because it is needed to always return the motor to the same position, even when the wiper switch is turned off (this gets interupted by a switch inside the motor when it has reached that "rest" position. The second 12V is the high speed. The third 12V input achieves the low speed. The "high speed" 12V signal stays on while the additionsl "low speed 12V signal is applied. I have to figure out how to wire the motor internally, so that this rpm drop occurs. In other words: In what part of the circuit, whenI apply the second 12V, would it cause the magnetic field to change so that the speed drops?....

    Best Regards, Tom
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    Do you have access to both ends of each field winding?
     
  5. tcolit

    Thread Starter New Member

    Aug 4, 2010
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    Yes, I do Bill. I have four wires coming from the two field windings and I can connect them any way I want (series or parallel)...
    I will try to make a sketch a little later to better show what I have...
     
  6. tcolit

    Thread Starter New Member

    Aug 4, 2010
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    Ok Bill. I made this diagram of the motor and the connection terminals to the car wiring. Please keep in mind that the internal wiring of the field and brushes is what I have come up with as the closest so far, but the whole thing may have been wired differently at any given connection. I'd welcome any input or questions.

    Thanks, Tom
     
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  7. BillB3857

    Senior Member

    Feb 28, 2009
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    This is only a guess but the weaker the field (within reason) the faster the motor will run. If one field and the armature get power, HI Speed. To get lower speed, the second field is energized, giving double the field strength, thus slower speed with the same armature voltage. The key will be to get the "phasing" right so that the 2nd field adds to the filed strength instead of canceling it. Tie one end of one field to ground and the other end of that field to the same lead that feeds the armature. If it runs backward, reverse the those two field wires. After you get it running the right direction like that, then tie one end of the other field to ground and while the motor is running, connect the free end of the 2nd field to 12 volts. If all is well, it will slow down. If it speeds up or stops, reverse the leads of the 2nd field. Again, this is only a guess but I think it has a fair chance of working for you.
     
  8. tcolit

    Thread Starter New Member

    Aug 4, 2010
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    Hi Bill

    I thought I'd give an update on the situation. In the end, I was able to locate two other working motors. My assumption that the motor goes to high speed by adding 12V to a second circuit was wrong. The high speed is achieved with 12 V only on this second circuit. From measuring the field coils I found something quite surprising: One side of the two field windings had a resistance of about 25 Ohms, while the other was only about 1.5Ohms. This doesn't make much sense to me as both coils look exactly identical to me, but of course they were wrapped with tape and sealed with lacquer and resin, so I couldn't look inside to see if they had the same wires sizes, etc. All I know is that the coil re-winging company that originally did my motor made both field coils identical. I could not get that one wired at all so that it would achieve two speeds. Always the same speed, no matter whether I wired one or both field coils together. The working motors I had for comparison both achieved high and low speed, depending on whether the high or low resistance field coil was energized. In short, I still can't make any sense of it all. I will have to find a used motor to finally get my original one working again... Unless you have any additional comments, thank you for you help Bill.

    Regards, Tom
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Glad to hear you finally got it figured out. It is a shame that the rewind shop didn't do their job correctly. It does happen, though. The difference in the good motor windings confirms my line of thinking about having different field strengths to control the speed. Hope you can find a good motor for your restoration.
     
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