hchris

3rd Brush Generator

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ken G</div><div class="ubbcode-body">To reinforce my remarks of somewhat earlier in this string, the owner's manual for my 1925 Rover says:

1. Under normal conditions, provided that the lamps and starter are used a fair amount, the battery should be kept on charge all the time during the winter and about half the day-time running in the summer.

2. Always keep the left-hand switch pointing to 'D' when the head lamps are in use. (That is the charging position; D for dynamo).

3. If the car is used for long tours in the day-time it is quite unnecessary to keep the charging switch 'on' all the time, as this will cause overcharging of the battery and consequent reduction of the acid level.

Ken G, 1925 Rover 16/50 (San Francisco) </div></div>

I guess England believed in more operator controls than American companies.

My 1930s American car has no operator controls to change the charging rate. And I think that was typical of many/most American cars. You opened the hood and adjusted the location of the third brush on the generator to set the charging to be about right on average. That meant seasonal changes (more lights and a higher starter requirement in winter than in summer, etc.) and for the type of driving the owner typically did. Basically this system was used because it was cheap and almost adequate, not because was technically good. If they were going to add controls to adjust the charging it was just about as easy to put a voltage regulator on the thing. Which they started doing just as soon as the accessory loads (radios, etc.) and increased lighting loads made the third brush systems woefully inadequate.

If your driving pattern is a number of small trips (neighborhood check out drives, etc.) with occasional long tours then you will be forever twiddling with the third brush adjustment. Or you will set it on the high side for the short trips and then run your lights on the tours.

But you can hide a electronic regulator under the cover where the judges can't see it and forget about actually using the third brush. Works for both long and short trips. Summer and winter. Day and night.

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Some things to consider.

The 3 brush generator with cutout uses the battery as the voltage regulator. The problem is any resistance or loss of connection to the battery will cause the generator voltage to raise. A loss of connection would cause the voltage to spike upwards of 60 volts burning out any light bulbs.

Modern technology has caught up and a touring car should put in a voltage regulator. It seems many are available that just fit in the generator and keep the voltage and charge rates appropriate.

Alternators are not needed, unless you are installing some big accessories like A/C. In the early cars the alternator could not put out high rates because the belt just can not be made tight enough. This is especially true on the Model A. Keep in mind how we used to adjust the belt on an alternator. It was considered too loose if you could turn the pulley with your finger.

For bulbs get the Australian made halogen bulbs. They are direct replacements for original bulbs and use marginally more current. They will give you a bright light, even with bad reflectors, that will allow you to drive 55 MPH at night. http://www.welcome.to/cvb

The ammeters in the cars can be way off. Just because it shows 10 to 15 amps does not mean that is real. You may want to confirm this with a known correct ammeter.

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I'm experiencing the same high-output problem with a third-brush generator and a fully-retracted third brush. Would adding a resistor in the line at the regulator's field terminal lower the overall output of a continuous 20-25 amps, which seems quite high? Just wondering.........

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The only other way to reduce the output is to rotate the entire brush holder assembly if possible.

There may be 2, 3 or 4 small screws which secure the assembly to the cover........hopefully on the outside.

Unfortunately I don't recall if you turn the brush holder against or with the rotation to reduce the output........  :unsure:

As I recall the closer the 3rd brush is to the next brush the higher the output so I would try getting it farther away whichever direction that might be.

Edited by cahartley (see edit history)

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I can never remember which way to move the 3rd brush either.  But I think it has to do with the rotation CW or CCW .

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 According to the manual for my car "move the third brush in direction of armature rotation to increase output, and in the opposite direction to decrease the charging rate."

 

 Have you taken a good look at the thermostat inside the generator? The thermostat is designed to decrease output when the generator gets to a specific temperature. On my car 1932 Auburn that temperature is 162 degrees Fahrenheit.

 

 Sorry if I'm repeating information already mentioned earlier.

 

                                              Carl.

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I'm experiencing the same high-output problem with a third-brush generator and a fully-retracted third brush. Would adding a resistor in the line at the regulator's field terminal lower the overall output of a continuous 20-25 amps, which seems quite high? Just wondering.........

A Zener diode will bleed off excess current. English motorcycles used a Zener diode for voltage regulation for many years. You need one with a value of around 7.5 volts for a 6 volt system.

Edited by Rusty_OToole (see edit history)

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37-44 Your 8-100 has a Delco system. 34-36 Auburns have an Auto-Lite system. If there is a thermostat in those I have never seen one.  I just hauled home a 898 coupe. I'll be into the generator shortley.

 

Rusty, the Zener diode is interesting.  I install a diode in the cutout, for the obvious,  could I hide one of those in there too.

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Zener diodes get hot as they turn excess electricity into heat. On the Brit bikes the only voltage regulator was the Zener diode and it was mounted on a fined aluminum heat sink up under  the steering head where it got plenty of air. If I put one on an old car it would go under the hood or under the car where a breeze would hit it while under way, and would mount it on a piece of aluminum sheet.

 

Later.... did a little checking online and found out the Zener diode is considered obsolete. There are better electronic voltage regulators available. I think they make them for cars with 3 brush generators so that would be the best solution.

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. . . Later.... did a little checking online and found out the Zener diode is considered obsolete. There are better electronic voltage regulators available. I think they make them for cars with 3 brush generators so that would be the best solution.

The third brush on my generator is disconnected and there is an electronic voltage regulator hidden under the brush band. Generator looks totally stock (and can be returned to stock if desired) but keeps the system voltage where it ought to be. Been in there for over 15 years. http://www.ply33.com/Repair/voltreg

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Hi Curt,

 

 You are correct the 1931-1933 Auburns have a Delco generator. I apologize if the subject was for Autolite generators, but assumed the adjustment might be similar. I've attached a picture of the thermostat in two pieces for the 1931-1933 Auburns.

 

                Carl

post-78300-0-57399900-1458167506_thumb.j

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In reading Spitfire8's post, he says "fully retracted 3rd brush". There is something very wrong here. The 3rd brush is meant to be in line with another brush (think its the ground brush) for making contact with segments on the commutator. As you adjust the 3rd brush there is more contact with the segments for higher current and as it is moved, its slightly out of line (phase) and you get less current. If Spitfire8's 3rd brush is fully retracted, there is something wrong. The unit should be pulled and inspected. I would predict the unit should produce between 12-18 amps when adjusting of the 3rd brush from one extreme to the other. Agree 20-25 is too high, you'll cook the battery. Output should be about zero on the ammeter with headlights on (or about 15 with them off).

Edited by Friartuck (see edit history)

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I've been touring regularly in an early 30s car with a 3rd brush generator.  For exclusive daytime driving I adjust the 3rd brush to just overcome the draw of the ignition circuit and a few extra amps so the ammeter shows about a +5 amps or so.  For nighttime driving I adjust it to give the same +5 on the ammeter with the headlights on.  Battery rarely needs water and they generally last 8 years or so.  If I had the 3rd brush adjusted for nighttime driving and find myself driving in the daylight without having set the charge rate down, then I just drive with the headlamps on until I have the opportunity to retard the charging rate - same technique knowledgeable drivers of the era commonly used.

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Very interesting comments all together, missing one, a third brush with an optima gel battery is not a good option, it will overload continuously, as I found out, could be the reason why there was no reaction changing the position of the brush.

The optima gel will also lead to a high voltage on the coil and other related parts. Be sure to check the voltage and amps on your third brush car . I've decided to go back to the lead battery on both my cars, because of this issue.

I could go to a regulated system, but hardly ever drive at night, so the third brush gen works well for me. 

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