You can check the field winding with an ohm-meter. If it's wired for 200V and 0.4A that is 500 ohms, 100V at 0.8A would be 125 ohms. It might read 10-20% lower than that because its cold. But a reading under 50 ohms or open would be cause for concern.
Also want to check insulation between both field and armature to the frame. A hipot tester is best, but an ohm-meter will find any shorts.
No guarantees, but I suspect that if you hook both armature and field to a car battery it will spin. Slowly and with not much torque, but it if it spins that is a good sign.
And of course, you can check the bearings by giving it a spin by hand. Brush drag will be a factor of course. You might want to see if there is easy access to the brushes. Brush condition and wear will tell you something, and if you can temporarily lift them off the commutator it will make it easier to evaluate the bearings.
Brush rigging is a
BIG concern with DC motors. The condition of the brushes themselves as well as the tightness of the brush rigging and condition of the armature. If the brushes are of acceptable length and the commutator is smooth, the rotating portion should be in good shape. And
bearings, of course. The commutator should be a bright dark brown, almost light chocolate color. Bright copper color means the comm has been machined since it was last run. Not a good sign there.
If it "lopes" or runs hot, there may be a problem with the armature. Testing that involves disassembly of the motor and use of a "growler". Best done by a motor shop where they are fimiliar with DC motors. A growler is a metal stand with a "V" block on top and the sensor element is a hacksaw blade. Even an automotive electric shop can make the test.
The field is simply an electro-magnet (usually 2 or 4 poles) around the "pole shoes". A "hi-pot" tester is not really necessary, a megger can be used. They are different instruments. An ohm-meter will show a solid ground but a megger will show a high voltage leak. With a 200 volt field, the ohm-meter will give an indication that the motor is usable, the megger will give a GO/NO GO usable test.
Any connection less than 500K ohms from an electrical lead to the frame is a NO GO condition, same as any motor. Brushes can be held lifted by pulling the brush just above the spring and letting the spring hold the brush in place. Easy way for checking bearings. . .
Using a car battery will yield a very low power supply. If it even runs at all. It won't hurt the field, even 120 volts AC continuously won't hurt it if it checks OK with an ohm-meter. Might hurt you though. . . With the brushes locked up, even the "A" leads can be powered with 120V to look for leaks. Some types of motors can be run as "universal" motors but I
don't think that one can. You
could hook it up a bridge rectifier to 120 AC, but that's getting into electrical pretty deep so watch your step. As a side note, "field weakening" is a process where a DC motor can be run
above base speed but speed regulation is seriously degraded. Staying with a "proper" controller per the nameplate is safer.
!! Residual magnatism of the pole shoes will cause the motor to run sometimes without the field powered up. Make sure the field is well protected, it could well "run away". That's dangerous for a DC motor.
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