Three-brush Generator Adjustable?

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Three-brush Generator Adjustable?

Postby Ironlegs » Thu Dec 13, 2012 7:55 am

My 1958 FCub has a 6-volt, three-brush generator. I inspected the generator brushes as part of my fall maintenance. The generator barely keeps the battery up...I have to put it on a charger about one a month (without using the lights). I was hoping to adjust the third brush but could not find any way to do this. Do any of you know (1) if these gens are adjustable and, if so, (2) how are they adjusted?
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Re: Three-brush Generator Adjustable?

Postby Rick Prentice » Thu Dec 13, 2012 9:28 am

Doing a search to "adjust generator" found this old post by Jim. Hope it helps:
I'm not going back through your posts to pick up the details. So I'm just going to assume you have a 4 position switch and a simple cut-out mounted on top of generator 1101355. If so, it should not be producing 15 to 20 amps. Extended operation at that rate will overheat the generator. The generator has 3 brushes. The third brush is adjustable to set the output. There is a screw in the back side of the generator. Loosening this screw (Do not remove it!) will allow you to move the third brush. Take the band off the generator and you can reach in with a screwdriver (while not running) and push the brush holder to a different position. Moving the third brush away from the brush it is closest to will reduce the output. You may have to give it as couple tries before you get the setting where you want it. Don't forget to tighten the screw when you are done.


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Re: Three-brush Generator Adjustable?

Postby Ironlegs » Thu Dec 13, 2012 10:56 am

After researching this topic a bit with Rudi's manuals, I see that my Cub has a "fixed" third generator brush and that the voltage regulator is the means by which battery charging is adjusted. The instrumentation necessary to make this adjustment is beyond the means of most users...the manuals talk about hiking-up the regulator's voltage setting by 0.3 VDC at a time...instrumentation is necessary to verify physical adjustments with voltage response. This explains why so many of these units suffer from insufficient charging...the adjustment is not obvious to make and the procedure is not openly disclosed.
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Re: Three-brush Generator Adjustable?

Postby Landreo » Thu Dec 13, 2012 3:20 pm

The 3rd brush adjustment is mostly for the output current regulation, not so much for the voltage. I presume it charged at one time so it is not a problem with the 3rd brush location. May be a problem from the generator insides all the way to include a bad battery. Did you check the battery voltage not running and voltage running?

Adjusting the voltage regulator is for the voltage output and can be done but you need a decent voltmeter with either an easy way to get at the regulator with the engine running or an adjustable power supply.
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Re: Three-brush Generator Adjustable?

Postby Bus Driver » Thu Dec 13, 2012 4:19 pm

While we are on this subject, it is potentially possible to set the third brush on the adjustable units to achieve an amperage output in excess of the rated amperage of the generator. Doing so risks burnout of the generator due to overheating. The earliest Cub generators had no cooling vents nor a fan on the pulley. Posting the numbers on the generator name plate is certain to bring a response showing the original amperage rating.
As already stated, reading the voltage at the battery with engine stopped AND with the engine running at a moderately high speed are the vital first steps in checking for charging system problems.
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Re: Three-brush Generator Adjustable?

Postby Ironlegs » Fri Dec 14, 2012 9:52 am

My Cub has an enclosed generator...no way for cooling air to enter and leave that's by design. The "no load" battery voltage is 6.53 Vdc. The battery was new April 2012 and the tractor has been run less than one hundred hours since replacement. I realize that correct battery voltage is best measured with an analog voltmeter/multi-meter...I usually borrow one from family when I'm addressing this problem (I have run and maintained a Super A for over twenty years). With the ignition on and engine stopped, battery voltage is around 6 Vdc. I have a bit of a phobia messing with the voltage regulator because I have had adventures with this device in the past. The Cub's gen and voltmeter were taken to a service garage where they were tested in April, at the time of replacing the battery. The technician made a slight adjustment to the regulator to tune it for voltage output...I wish I could remember better how this was done.
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Re: Three-brush Generator Adjustable?

Postby Jim Becker » Fri Dec 14, 2012 10:09 am

Ironlegs wrote: The Cub's gen and voltmeter were taken to a service garage where they were tested in April, at the time of replacing the battery. The technician made a slight adjustment to the regulator to tune it for voltage output...I wish I could remember better how this was done.

If both units were checked by a professional that recently, it is unlikely anything is wrong with them now. Have you had the charging problem ever since then or is it more recent? There is a slight chance the "slight adjustment" left the voltage output a little low, which would cause your problen. However, the most likely problem is a bad connection. Check all the wires and conncetions in the charging circuit INCLUDING THE GROUNDS.
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Re: Three-brush Generator Adjustable?

Postby Eugene » Fri Dec 14, 2012 11:10 am

Ironlegs wrote:The generator barely keeps the battery up...I have to put it on a charger about one a month (without using the lights).
Currently thinking the problem may not be with the generator/regulator. Thinking you have a battery drain when engine is not running.

Engine off, all switches off. Take voltage reading between battery terminals. You can do this with any volt/multimeter and get an accurate reading.

Disconnect the battery ground cable. Take a voltage reading between the ground battery terminal and the ground battery cable. Voltage reading should be zero.

The "no load" battery voltage is 6.53 Vdc.
Question, engine running at about 1/2 throttle, amp meter reading charge when reading taken or was the reading taken at the battery with the engine off?
With the ignition on and engine stopped, battery voltage is around 6 Vdc.
Why ignition on?

Agree with Jim. Clean up all connections.
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Re: Three-brush Generator Adjustable?

Postby mrdibs » Mon Dec 17, 2012 1:14 pm

Are you sure it's charging at all? My generator was toast all summer and I rarely needed to charge the battery (not using headlights). I finally ended up at the rebuild shop and one of my field coils was bad. Had I been able to get those dang screws out, it would have been a $20 fix. But I couldn't so it was much more, though they did a complete rebuild including paint.
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