A friend of mine is going to give me an old Dayton 8F047 which I would like to recycle, but it is now obsolete and I cannot find anything other than a schematic which is reproduced below.


simulate this circuit – Schematic created using CircuitLab

It looks like a separately excited DC motor aka "universal motor", which also works with AC, and I'd just need to wire the auxiliary and main windings in series to make it work I think. I assume the start switch (which is really illustrated like that...) is a physical external button (please shout if it is an internal component essential to how it works), but I can't make sense of the so-called "protector" (which is illustrated as a circle) which is in the way of the main winding, so I'm confused now. I don't want to try things randomly and burn it...

I found this and that on the internet, but I don't know how grounding either end of the auxiliary without supplying it with any power can change its direction, and I don't know what's inside the UL Limit.

What is this type of motor and how am I supposed to control it?

  • \$\begingroup\$ I'm no motor expert but it looks to me like the 120V return is for voltage sensing. I believe the direction is imposed by the polarity of the Aux winding. IIRC the direction of the rotor is due to how both magnetic fluxes interfere with each other at a given time, regardless of whether this is AC or DC in this case. Reverse one flux and the rotor spins in the other direction. Someone might want to confirm this. \$\endgroup\$ – user59864 Mar 14 '16 at 8:58

If it does not have a commutator it is not an AC/DC motor. It will be a single phase induction motor. Universal motors have a commutator and the field is wired in series with the armature. Universal motors resemble the series DC motor in their construction. They are sometimes called AC/DC motors.

If your motor has a commutator that has its brushes shorted and the mains going into the field then it's a repulsion motor, which are popular in the USA for their superior starting torque compared to other single phase induction motors. From what you have drawn I think you have an induction motor.

  • 2
    \$\begingroup\$ If it's an induction motor, you need an external "start capacitor" which will define the rotation direction, and the "start switch" will be an internal centrifugal switch to disconnect the start winding at speed. Searching for "capacitor start" motors should yield wiring instructions. \$\endgroup\$ – Brian Drummond Mar 14 '16 at 12:45
  • \$\begingroup\$ Thanks a lot both of you. It looks like the wirings I've seen are compatible with this type of motor - but what end of the main winding should I use? "Hot" or "return"? Does it have something to do with direction of rotation? \$\endgroup\$ – user42875 Mar 14 '16 at 14:42
  • \$\begingroup\$ Isn't that a simple current limiting resistor instead? \$\endgroup\$ – user42875 Mar 14 '16 at 16:20

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