3rd brush adjustment procedure

M

mcgarrett

Well-known member
Wanting to confirm that in order to adjust the 3rd brush in a Model A generator (not a Powerhouse) I will need to remove the generator. Please advise if this is not correct.
Thanks in advance for the input.
 
Remove the rear band by loosening its screw and sliding it off the back of the generator. Connect a voltmeter across the battery's terminals. Run the engine at a fast idle. Using a wood dowel or plastic rod, rotate the 3rd brush up or down to get a reading of 7.5 Volts. If your drive at night, adjust the generator with the high beam headlights on.

It takes at least 2.5Volts to charge each battery cell, so for a 6Vbattery, 3 cells x 2.5 = 7.5 Volts.
A lesser way of making an adjustment is to move the 3rd brush until the ammeter in the instrument panel reads 8 Amps, or 10 Amps with the headlights on.
 
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An easy rule to remember:
To move the charging rate UP, push the third brush DOWN;
To move the charging rate DOWN, push the 3rd brush UP.

Marshall
 
move it in the direction of rotation to increase the charge rate , or in the opposite direction of rotation to decrease the. rate.
Lawrie
 
While you're adjusting it just watch the ammeter. Make an adjustment, raise the engine speed and look at the ammeter. Should be 3-5 amps for normal day driving.
 
The charging rate of the generator needs to be adjusted according to how the car is driven and the season (time of the year, winter or summer). The Ford technicians were instructed to measure the battery's electrolyte specific gravity and adjust the charging rate accordingly.

The generator can be modified to use a voltage regulator that can be mounted on the firewall or hidden somewhere. That will automatically adjust the charging rate for different driving conditions. I believe voltage regulators are available that mount inside the generator.
 
I appreciate all the replies. So there is NO screw to loosen or tighten? That would certainly make adjustment easier. Looking into the generator with the band removed, I can see the 3rd brush and it looks like there is a screw holding a clip that secures it down so that it can't drift out of adjustment, but maybe I'm wrong. I've never adjusted a Model A generator, so I'll give it a try tomorrow and see if it will move by prying as has been suggested.
 
There is a spring (Item #42 in this diagram from Bratton's) with a screw that holds your setting, but it is made to be pushed without more than a dowel to the desired setting.

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The screw head you see is the screw what secures the brush to the brush carrier . Do not try to unscrew that !!! . The 3rd brush is designed to be moved by hand I never use a dowel or screwdriver .Stick you finger in and you can push the 3rd brush carrier up or down to the required charging rate . Sometimes it is stiff to move as it might have been a long time since last adjustment but it will move trust me . Only do this with the engine stopped or this could mess up your nail varnish !!!

John in very hot summer morning Suffolk County England .
 
In the illustration, there is a V shaped spring steel piece that is fastened to the rear support and it applies tension to the third brush adjustment ring. It should have enough tension to keep the ring anywhere it may be adjusted to. The main brushes are situated where the power brush is on the left side and the ground brush is on the right. The third brush is situated above the power brush. When the third brush is moved closer to the power brush, the amperage output increases and the opposite happens when moved away from the power brush.

The ammeter indicates the output so Ford instructions were to use it to adjust between daytime operation and night time. The Fun Projects cut out voltage regulators are no longer available but I think the brush cover band type regulators may still be sourcable from the original designer of this type. The regulators were the only way to limit both need for adjustment and prevent constant overcharging of the battery.
 
I set my third brush to about 8 amps charge . On long runs during daylight I will put on the parking lights and the charge drops to approx zero ,kind of a guestimate thing . Most moderns run with lights on anyway so you do not look odd . Been doing it for years seems to work OK .

John in same place same weather .
 
john charlton,
thank you for your comments. Also, to add some context to your remarks about the heat where you are there in Suffolk County, it's been 106 to 108 degrees Fahrenheit here in Texas for the last week or so! Cheers! :)
 
Well, I have successfully located and adjusted the 3rd brush to where it is charging at about 10 amps while driving at 30 mph. I presume that is where it should be for normal daytime driving?
Thanks to everyone for their input!
 
FWIW - I have my 3rd brush at is lowest setting. This gives me 4-5 amps on the gauge, which keeps the battery charged just fine.
 
I also have mine set at 3-5 amps. I don't drive at night, but do take long trips. I find this setting to perfect. I don't have to add water to the battery. I don't like to over charge, plus it can cook the water out of your battery.
 
I use my 31 Budd CCPU very frequently on very short trips . These are easy walking distance but dodgy left ankle ( OK on a bike and short term clutch pushing) has stopped anything over a couple of hundred yards . The about 8 amp charge keeps my battery up the way I use the truck . Horses for courses as they say .

John in same place same weather .
 
I have a related problem. Moving the third brush in my generator makes little or no difference to the output current. Although the generator is putting out 7.5 volts or more, the amps hover around 1.5 - 3. This is sufficient to balance the ignition load but turning on the lights results in an 8 - 10 amp discharge. Could there be an abnormally high internal resistance in the generator?

All measurements of volts and amps were made using a high quality Avometer which unfortunately no longer measures resistance. Using a cheap and unreliable digital multimeter the resistance between the generator output terminal and the case is approx. 0.4 ohms. This seems too high and I should look inside for the problem.

Am I right?
 
Isimpson - your field coils may be partially grounded due to deteriorated insulation. Moving the 3rd brush should make a sugnificant difference.

Here is a short demonstration video I made about adjusting the 3rd brush.

https://youtu.be/PL94VX3GIq8
 
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