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3rd Brush Generator


hchris

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Having a 1930s car with 3 brush generator installed I recently completed a week long tour and noticed that the amp meter showed a consistent 15 - 20 amp charge all day long. I moved the third brush from one extreme of adjustment to the other but could not reduce the output below these figures, I finally resorted to driving an hour or two at a time with headlights on which caused the amp meter to drop back to the centre of gauge.

Whilst I expect to see a high charge rate initially after using the starter motor I would expect for this rate to drop off as the battery recharged, I might add the battery is almost new and in good condition.

Am I being overly concerned with this situation ?

My maintenance manual says to set up the generator I should position the third brush to give an output of 22amps / 8.2 volts at 1800rpm, my concern is that these are the maximum output figures under full load, I expect that on a lenghty daytime drive I should see little or no charge on the amp meter once the battery is recharged after start, or have I got it all wrong ??

Any old sparkies out there with this background ??

Thanks

Chris

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It appears you have a "CUT OUT" rather than a "VOLTAGE REGULATOR" electrical system. The voltage regulator was not used till the middle to late 30's and later. Your expected results describe the feature of the voltage regulator.

The cut out system operates as you described. The cut out will not permit charging until the voltage in greater than 7 or 8 volts. At this time the connection will close and continue to charge even when the battery is fully charged. The cut out is designed to avoid draining the battery when the generator is creating less than 6 volts. Physically, the cut out usually sits on the generator and is about 2 1/2 inches long, 1 inch wide, and 2 inches high. It will have one wire from the generator and a second wire to the battery.

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In my opinion the system of third brush regulation is a very poor match for a touring car: Long sitting and in season weekend local trips with occasional long tours just don't fit into the originally anticipated usage pattern.

So I hid an electronic regulator under the brush cover (a fully reversible modification). See:

http://www.ply33.com/Repair/voltreg

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Huptoy is correct and there is nothing wrong with your generator. Admittedly it takes some getting used to. I've heard of people who will drive an hr or so and then turn their lights on for an hour but I've never found the need to do this. The battery will not overcharge or evaporate the water quickly. At least it hasn't in mine.

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Huptoy and rbl2 are correct. The only reason that I went to a 6 volt alternator is that I drive a lot at night and the old three brush generator didn't have enough out put to carry 50 cp bulbs for hours on end.

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I concluded after my .... actually during my first night time drive with my 26 that it would be my last night time drive. Those lights might have been bright enough in 1926 but that was a very long time ago and they just don't do the job.

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OK thanks for the replies, I was unsure of the regulating capabilities of third brush systems; seems like the battery resistance is the only control factor.

Hmmmmm just wondering if resilvering the headlights will improve my braking ?

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The fastest I've ever had my 26 was 57 mph. That was in the day time and it toook a half a mile or so to get it that fast. I don't recall how much candle power the headlights have but I do know it isn't enough.

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It's interesting how much difference increasing the displacement to 200 ci, the compression to 5:1 and increasing the carb diameter by 3/16 of and inch made. The 26, 27 and 28 that I had really ran out of puff about 45 mph. My late 28 and 29 would easily make 55mph and my 30 (daily driver) will actually pass 70 mph (by the stopwatch). The 31 that I had was still faster on the acceleration (probably because it was 2 1/2 inches lower and had a better carb.

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My lights are no better than any one else with a 31 car. I have had the headlights silvered but they are still not great. I don't drive after dark very often. When I am out of town, I use red and white bicycle flashers and attach them to the front and rear bumpers. I set them to flashing and they do get the attention I desire. Vehicles give me respect as they can see the flashing lights from a long way off. Without the flashers, cars come very close before passing but with the flashers they change lanes about 200 feet back.

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My lights have been resilvered also but like yours, I'm not impressed.

I've thought of attaching reflectors but never thought of flashers. My car doesn't have bumpers, they were an option. I'll have to attach them to the springs I guess.

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Not to hijack this thread, but I had a company in Oregon restore the reflectors on a Graham I once owned and they were nearly as bright as sealed beams. The company name was UVIRA and you can probably find them in Google. They electroplate aluminum to the steal reflectors and then polish them to a high luster. Silver starts to tarnish as soon as it is applied. Not cheap, but well worth the price. I guess if I still owned a car with electric lights, I would do it again.

Frank

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Check your field windings to be sure they are not grounded due to insulation breakdown. I had a 37 Plymouth that had a bad field coil and the charge rate could not be adjusted. It overcharged and the faster you drove, the higher the amps went. Replaced the windings and cured the problem. Richard in North Carolina.

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Nobody clearly explained the property of a 3rd brush generator. Once the engine is running at more than idle, the generator delivers substantially the same current (number of amps) irrespective of engine speed. The manufacturer's intention was that that current was sufficient to supply all that could be turned on (mainly lights, of course) and the excess current went into charging the battery. Thus if most of the driving is by day with no lights, the battery gets overcharged and boils dry. Hence there is normally a switch that turns on the generator, sometimes with two different current choices, with a position that disables it, so when you estimate that the battery is fully charged, you turn off the generator. At least, that is how it is on my 1925 Rover. Of course, this begs the question of how to estimate full charge!

Ken G, 1925 Rover 16/50, San Francisco

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Thanks Ken, I pretty much gave up on further comments after the thread was corrupted by all the other unrelated brakes and lighting junk.

I have come to the conclusion that the generator output, once set by the third brush, will remain high under no load conditions and one has to live with it by keeping an eye on the battery electrolyte levels; especially when long daytime runs are involved.

Chris H

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Chris, I came to the same conclusion as you with my car. So far I haven't had any problems. I'm told that some people, when on a long run, will turn their headlights on to keep from overcharging but I doubt that is necessary. After all, back in the day I doubt people worried about overcharging their batteries and I have not seen any mention of it in the original books.

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My 1917 Series 9 Franklin has a 3 brush Dyneto starter-generator without a cutout. The system charges the battery at speeds greater than 10mph. The current output follows a curve maxing at 21mph. The starting switch has a "Neutral" position which is used for "country driving and long trips." Operating instructions say switch from "Start" to "Neutral" after 30 minutes of allowing the battery to recharge from starting in order to avoid cooking the battery. Since the starter-generator operates as a motor below 10mph, the switch is left in "Start" position for "city driving, except in congested traffic, when switch should be at 'Neutral' to avoid undue discharge of battery." There are no instructions for what to do at night with the lights on.

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Just a general comment about amp meters -- there are several different ways to connect the amp meter, and the reading you get will mean different things depending on how it is connected in your car.

If the meter is connected in the battery lead, that is, between the battery and the rest of the electrical system, then you are reading what is going into or coming out of the battery + amps for charging and - amps for discharging.

Normal operation on this system would have the meter near zero most of the time after the battery has been recharged after starting, regardless of which electrical devices are being operated.

The other way to connect the meter is in the generator or alternator output lead. In this case the meter is reading generator output and it will not usually have a negative side to the scale. Normal operation here is to read higher amps just after starting as the battery is being recharged, lower amps in the day time with no lights and higher amps as lights or more electrical equipment is turned on.

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From my understanding most vehicles of this era have a centre zero ammeter, as you first described, and that is the type fitted to my vehicle; it shows the current flow to and from the battery.

The problem with the other (load style) ammeter is that you cannot tell if the generator has failed; hence you will be running on battery output until it also fails.

Chris H

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  • 3 weeks later...

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)

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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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  • 7 years later...

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.

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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.

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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).

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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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