FIELD COIL AND BRUSH ASSEMBLIES

TALE OF TWO MOTORS: The next photo is a shot of the two field coils of a Prestolite starter motor (minus the brush assembly) versus a four field coils Prestolite windlass motor. The two coil assembly came out of the casing I used as replacement for my corroded windlass motor casing. I installed a new four field and brush assembly ino it. Three main types of DC motors are SERIES, PARALLEL (also known as SHUNT), and a COMBINATION of the two (which is what WM 7003 is). SERIES DC motors have fields coils that are wound of heavy copper ribbon that has minimal resistance (like the two field above) which insures high current the instant it is turned on - which leads to the series characteristic of high starting torque. In a series motor there is only one path for the current to flow, so all the current that goes through the field coils also goes through the armmature. In PARALLEL DC motors the current separates onto two circuits, one gooing thru the field coils and the other going through the armature. This arrangement allows more control over the speed of the motor, so constant speed is a characteristic of a parallel wired DC motor. The field coils of a parallel motor are made of relatively thin wire that has more resistance than the series motor copper ribbon coils. COMBINATION DC motors combine SERIES and PARALLEL motor characterristics to get the required operating characteristics for the task at hand.
With the series and parallel motor characteristics in mind, hopefully you can take a look at the two differrent field coil assemblies shown, and see that the Prestolite two coil starter field coils are from a series motor, while the windlass four field coil assembly is a combination of three field coils wired in series combined with a field coil wired in parallel. Note the three "ribbon" coils in the back (wired in series) versus the wire coil in front wired in parallel.
Though you can buy brushes, pole shoes, etc. (as I did), the best thing to do is buy the field coil and brush assembly as a unit (about $50). If the pole screws are esentially rust welded into the case and pole shoe you may have to drill them out (as I did) - be careful not to damage the casing threads if you are going to reuse the case. You will probably have to have new pole shoes and screws. So while I learned a lot by this rebuild process, if I had already known all of it I would definitely have bought the assembled motor (next time) - and considering the time and money spent I would have definitely saved money purchasing the assembled motor!!!!

next photo "POLE SHOE ORIENTATION"