What's the purpose of a shunt field in a 530 starter?

Randy G · Feb 5, 2016

I'm rebuilding a 530 starter and it has a shunt field. What is the purpose of it and how do you test the field housing for shorts? I know its got to be a different process than testing a 520 starter w/o a shunt field in the housing. Starter works fine, I just want to learn something new.

buickanddeere · Feb 5, 2016

??? It's not just a series field winding ?

Randy G · Feb 5, 2016

Nope, it has a shunt field as well.

Mike M · Feb 5, 2016

I do not know why they would put one in there ? Most tractors do not use them. I have seen some in autos though. Seen some tractors with only 2 coils where there was place for 4 so we replace with 4 full field coils. I thought you just check it for continuity thru the coils and then make sure it is not any going to ground which is the case.
I did have a 530 and come to think it turned over sort of slow so maybe it had one in it. I don't know why they would of done that ? Ask a local rebuild shop to see if they show a listing of replacement coils with 4 full field coils.

Randy G · Feb 5, 2016

Mike,

Here is my understanding but not sure. I think the shunt is wired to keep the armature from spinning at full speed to keep from destroying it self but yet provide a constant amount of volts/amps to power though the cranking process. I would still like to know how to test the field housing for shorts though.

Tramway Guy · Feb 5, 2016

From what-when-how.com:
"The compound wound motor (Fig. 15.12 C) is a combination of shunt and series wound motors. The characteristics can vary depending on how the field windings are connected. This variation is due to whether the shunt winding is connected either across the armature or across the armature and series winding. Large starter motors are often compound wound and are operated in two stages. In the first stage, the shunt winding is connected in series with the armature, so that a low meshing torque is attained due to the resistance of the shunt winding. During starting when the pinion of the starter is fully in mesh with the ring gear a set of contacts causes the main supply to be passed through the series winding and armature, giving full torque.
The shunt winding is now connected in parallel with the armature so that it acts to limit the maximum speed of the motor. This is the second stage operation."

Lee B · Feb 5, 2016

Two effects possible with a shunt field, one would be to limit RPM of the starter, sounds counter intuitive as quite a few things electromagnetic do but the addition of this magnetic field would induce counter rotation forces within the turning armature. The faster it turns over the harder the brakes are applied. Second combinational effect is to increase very low RPM stater torque, in effect getting the big engine to begin rolling over easier. Any possibility that it was not wound professionally and this might be a mistake? Some rouge starter rebuilding shop with a better idea? Interesting find no matter the case, I did not know they would do this. It would also be interesting to hear this one working beside a standard issue starter to see if one can hear the difference - in other words did the better idea actually pan out with noticeable/desirable results? Might be a case of some like it and others don't.

Randy G · Feb 5, 2016

I would still like to know how to test the field housing for shorts though.

Mike M · Feb 6, 2016

Take the whole thing apart but leave the field coils in the case. They should be insulated from the metal case. Test with a continuity meter from the windings to the case you should not have any. If you suspect it might have a short that only happens at voltage then take a battery and jumper cables. Hook one side to the field windings then touch the other cable to the case and see if sparks fly.
If you suspect the coils are shorted to each other ? then careful visual inspection usually spots the burnt spot. Might even be a measurement to test amp draw of the coils if you can find the specs.

What's the purpose of a shunt field in a 530 starter?

Randy G

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