Re: Blew up the generator....

Posted by John Regan on Sep. 21, 1998 at 10:35:53

In Reply to: Blew up the generator....
posted by J.R. Aiello on Sep. 20, 1998 at 21:54:03

: Ok, assuming that I HAVE blown up my generator and overcharged my battery (previous message), what can I do about it? Can I fix it, do I replace it, or send it away for repair?

: On the same topic, I heard that putting the 20 amps into the battery is because of the 3rd brush. What is it? Where is it, and how do I change it? I've removed the generator, but haven't taken it apart yet. Every time I order the Model A Mechanics book, or some others, they are always back ordered.

: I do have 35 years of Restorer/Model A News. Does anyone have an index of them that would show which issue I could look in?

: Thanks for your patience. I'm real new to this, as you can tell.

: J.R.

You may not have hurt the generator unless you drove it for a fair amount of time.Take the dust cover band off the back end and look inside for any signs of solder being thrown out.If you see this then you probably ought to have it looked at by someone who knows Model A generators.ALAS the typical modern motor shops usually claim to know all about them but rarely do.I have had lots of problems with local shops and no longer attempt to take generators to anyone but a competant antique hobbyist type rebuilder.My favorite rebuilder just retired from doing it so I am in the same boat as you.

The typical Model A generator has 3 brushs inside.2 of the brushes are mounted exactly 180 degrees apart and are fixed.These are generally referred to as the main brush assembly.The other brush is mounted on a separate plate that rotates in the same plane as the fixed brush assembly.For all 3 brush generators you get more output when you rotate the 3rd brush assembly in the same direction as the generator normally turns - clockwise as viewed from the front of the car.If the 3rd brush plate is loose then the generator can advance itself which is a real problem.I have seen folks remove the 3rd brush and connect the field across the output for max output.Those generators don't last very long.You should be able to locate the locking stud or screw that holds the plate from rotating.It generally has a slotted hole depending on the generator you have.You should be able to set the generator to almost no output or to full 18 amps with this setting either fully CCW or fully CW respectively.You should never set the generator for more than 15 amps continuous running.

Be advised that there is also a thing called a "power house" generator that was on some A's.These are capable of much higher output (over 25 amps).These have 5 brushes and are a different animal but they do still have an adjustable 3rd brush.If you think you have one of those then you probably did not hurt it at 20 amps since those can go far beyond that setting.Even though they can - you shouldn't think about setting up that high for all the reasons already mentioned.

The fields are wired in series with one free end going to the 3rd brush and the other free end going to ground either internally or externally.Often when grounded externally the armature connection is a heavy wire and both the field connection (smaller wire) and armature connection pass thru the same grommet to the outside world.Otherwise the free end is grounded internally and the armature connection is brought out thru a stud thru the side of the generator.On some the armature wire is simply brought out by itself and one can assume the field is grounded internally.

I hope this gets you familiar with the generator you have.It is not enough info to attempt a rebuild but it should give you a map of the area and the location of the mine fields.

FINAL CAUTION - NEVER RUN A 3 BRUSH GENERATOR WITH NO LOAD CONNECTED TO THE ARMATURE OR YOU WILL DAMAGE IT.If you want to spin it up to check bearings and such then connect the heavy armature wire directly to the case of the generator.I know this sounds wrong but it is absolutely correct.This grounding of the armature also in effect grounds the field which is tapped down on the armature via the 3rd brush.You can also spin it up safely if either end of the field winding is left open.




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