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  • dc motor ?

    I have a 90 volt dc 1/2 H.P. motor with 4 wires. The wires marked A1 and A2 make it run. What are the 2 wires marked P1 and P2 used for? I can cap them off, but I'm just curious. Thanks.

  • #2
    If the wires are light guage they could be a tachometer winding for speed sensing.
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    • #3
      Those are the internal thermostat connections. Use P1 and P2 to control a power on relay to A1 and A2. If the motor overheats, P1/P2 break connection (switch open) and thus will turn off the power relay.

      You don't have to use these but it's a good idea if the motor is used in a heavy load or constant run environment.

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      • #4
        Seems to me that you would want to use something that requires a manual reset in the circuit to prevent unexpected starts after the motor cools down. It might even be required by the applicable codes or by OSHA.

        Is there a reset button built into the power relay or incorporated into the motor itself?

        Roger

        Any products mentioned in my posts have been endorsed by their manufacturer.

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        • #5
          Winchman No reset button on motor. Don't know what I'm going to do with it yet. Got a skid full of dc stuff at auction.

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          • #6
            Sometimes field connection.. Sometimes heat snap action switch, sometimes a tach..

            Have to know the motor or the labels denoting such..

            Post a picture of what you got? you going to ebay it?

            David

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            • #7
              CCWKEN is right, it's an internal thermostat. I don't Ebay. Just collect. I got three 1 horse dc motors and controllers plus right angle drives. all new stuff for $150.00

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              • #8
                Ray:

                Reading at speed always has a disadvantage.

                I re-read the post and figured out I skipped the descriptive. (P1 P2 labels) Oops. I gave a answer on dc motor leads in general.

                Last time that happened I melted down a control. Sometimes it pays to read slower and digest more. I do accomplish a lot working at light speed, but make some really stupid mistakes at times.

                David

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                • #9
                  A few easy checks for a permanent magnet motor: spin the shaft by hand, then connect two wires together, spin the shaft again. If you have increased resistance to turning, you have the brush leads in your hand. Note this does not work for any motor, ac or dc, that doesn't use permanent magnets. Another way to check this is if there's any field winding at all, it's not a permag motor. Permags simply do not have a field winding, and in the case of a reversed magnetic structure, where the magnet is in the armature, there will be no armature wiring at all. In this case, there will need to be a control circuit dedicated to that motor, or there's no way to run it. So unlikely that you would ever run into such a motor, except in the field of model airplanes, where these motors have an awsome power/weight ratio, and power/size ratio. It's still hard for me to grasp the concept of having a two or three horse motor that you can wrap your fingers around. Anyway, I digress.
                  Then check any remaining wires. If you have more than one pair of wires that, when connected together, increase the hand force needed to spin the shaft, then you have a motor with four brushes. All these treadmill motors I've seen have been two brush.
                  Whatever wires remain, check them with an ohmeter. If the resistance is lower than an ohm or so, that would be a thermal cutout. If the resistance is above ten or so ohms, that would be a tach coil.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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