31 Caddy

3rd Brush Generator Help Requested

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Hi all. Need help with a Delco 927D Generator installed on my 1931 Cadillac 355A convertible coupe. This is a positive ground system and uses no voltage regulator (other than the cars' battery, lol)  Amperage is adjusted by loosening a small screw on the end plate and rotating the third brush in the direction of rotation, positioning it closer to one of the adjacent brushes. A cutout relay mounted on top of the generator, opens to prevent the battery from discharging through the generator at low RPM. A thermostatic switch within the generator, reduces output above approx 165 deg.

 The engine in this restoration project car was completely rebuilt about 25 yrs ago, including the generator and the car went into good storage. I have had the engine apart and verified this, and now the car is in the process of reassembly. I installed a complete reproduction wire harness and conduits. The battery is a NAPA 6 volt - not an Optima. The dash is reinstalled, and the body back on the chassis and painted. I have driven it around the neighborhood, sans fenders and hood ( looks like a highboy, lol ) and all is well except for that pesky generator won't show a charge. The ammeter shows a big discharge when cranking, and recovers to a very slight discharge with the engine running, but will never go positive. Here are some things I have tried, in no particular order:

1) Read battery voltage only (5.9 - 6.4 on battery side of cutout relay with engine running at about 1300 RPM. Reads 0 VDC on generator side of cut out relay.)

2) Held contacts closed on cutout relay. Reads battery voltage only on both sides of relay. Bypassing the relay did not result in any generator output. This should have served to polarize the generator as well if required, I believe. Installed an NOS cutout relay - no help.

3) Rotated third brush to full increase position - no help.

4) Battery is grounded to a starter housing bolt. Also have a good ground cable between the engine and the frame.

5) Removed generator and disassembled. End plate clean as new. Commutator very clean, and not grooved. Brushes look brand new and are free in the holders, which also appear as new. Bearings new. Everything clean and tidy. One brush is grounded  by a wire to the end plate and that brush reads continuity through that wire to ground. The second brush is connected by a wire to the gen terminal on the external cutout relay. That wire reads continuity. The adjustable 3rd brush is connected by a wire through the field coils and thence to the thermostatic switch and through it to ground. This appears correct to me from schematics, but how would I differentiate a continuous set of coils as opposed to a short to the case? The thermostatic switch is grounded anyway. In fact with all three brushes contacting the commutator, I can read continuity all the way from the external cutout relay wire through the second brush, through the commutator, through the third brush, through the field coils, and all the way to the thermostatic switch/case. Is this correct??? Again, what would be the difference between a wire shorted to the case along this path, and a reading showing a good, unbroken set of coils, etc???

6) Finding nothing obvious, I prayed over it and reinstalled it. While I DO  believe in the power of prayer, the Lord is not my errand boy, and the generator is still not charging.

I don't have a growler and don't know how to test the armature. As indicated above, I am not sure of the field coils. I have several old non rebuilt generators of the same model, that I made some continuity tests on, with the same results, though all three could be bad. (One of them looked like it was run for 200K miles before being submerged for several years anyway, lol.) The more obvious problem is that I am a novice, and really don't know what the heck I'm doing, which is why I penned this tome, begging for your assistance.

Forgive the length of this. I really like to fix things myself when possible, which is I why I didn't take it to a generator shop to start with. Usually, most problems are solved by something obvious and simple anyway. Barring some great idea on your part, I suppose I have no choice but to surrender, yank it back off and take it somewhere where they can test the armature and field coils. Thanks for reading, and thanks in advance for sharing your knowledge.

Edited by 31 Caddy (see edit history)

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The 3rd brush generator system uses three brushes, 1) Positive output, 2) Ground, and 3) Adjustment brush. The Output and the Ground should be opposite each other and the 3rd brush is between the two. The 3rd brush is connected to the one of the shunt field coils and the other end of the field coils is connected to the ground brush.  Movement of the 3rd brush affects the magnetic force between the poles via its contact through the copper armature segments it touches. The 3rd brush controls the output as an angular relationship between it and the ground brush.

Some checks for you to perform:

1. Are any of the field coils shorted against the case (grounding out) or each other? A field coil that is shorting against itself will not produce the magnetism needed.

2. Is there continuity from the 3rd brush and the field coil closest to it?

3. Are the field coils connected to each other? The total resistance should be a multiple of a single field coil measurement. If a single field coil measures 50 ohms, then total would be 100 ohms for a two pole generator and 200 ohms for a four pole and so on.

4. Is the one end of the field coil (the last in the series) connected to the ground brush?

5. Is there some residual magnetism in the poles? You may have to flash the field coils to get them magnetized by momentarily connecting them to a battery.

6. Check the thermostatic protection portion in the 3rd brush circuit.

7. The attached should be similar to your DELCO unit.

PM me for more checks, etc.

 

3rdbrushgenerator.jpg

Edited by Friartuck
Added reference page. (see edit history)

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You mentioned a new wiring harness. It's possible the wire from the generator is connected to the wrong lead on the ammeter. I've seen this before. Often times when the wiring harness is made, one of the ring terminals to the ammeter has two wires crimped into it. If the wiring harness manufacturer made a mistake and crimped the generator wire to the wrong lead, i.e. the battery lead, then the ammeter would only ever show discharge, even though the generator is charging properly.

 

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You say "the ammeter shows a big discharge when cranking."  That is not right. The meter should only show the coil current draw.

'

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On my 28 341B the thermostat was missing. I installed a electronic regulator that is hidden inside the generator housing so it looks standard. With that there is no need for the thermostat or the third brush. James Peterson in Bend Oregon makes the electronic voltage regulator for 6 volt generators for the Ford people but could 

posibly build one for your Delco unit. Very reasonably priced IMHO. Friartuck has made some excellent points that need to be checked out as the basics need to be correct. 

 

Jim Bourque

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45 minutes ago, Jim Bourque said:

On my 28 341B the thermostat was missing. I installed a electronic regulator that is hidden inside the generator housing so it looks standard. With that there is no need for the thermostat or the third brush. James Peterson in Bend Oregon makes the electronic voltage regulator for 6 volt generators for the Ford people but could 

posibly build one for your Delco unit. Very reasonably priced IMHO. Friartuck has made some excellent points that need to be checked out as the basics need to be correct. 

 

Jim Bourque

I believe that James got started by making one for a Delco-Remy equipped Buick, and his version for a Delco-Remy fit perfectly in my Plymouth (Chrysler used Delco-Remy through 1934). I'm pretty sure he would have a version to fit other late 20s through early 30s Delco-Remy equipped cars and I highly recommend getting one.

 

To the original question, if there is 0 volts showing on the generator side of the cutout then it sounds like the generator is not producing at all. If rebuilt and never used, the soft iron cores of the field windings may have to be magnetized. This is sometimes called "flashing the generator" or erroneously "flashing the regulator".

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2 hours ago, Owen_Dyneto said:
2 hours ago, Alfa said:

I would love to know what a Growler is !!!!!????

A growler is a device to check the electrical integrity of an armature.  A very standard piece of equipment in the trade.

 

A fairly good description is only an Internet search away.

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In essence a Growler tester produces the magnetic fields that are found in a generator or starter armature. It simulates how the armature would perform under normal conditions. Initially a rebuilder does this test first when diagnosing a unit for repair.  It can test for either short or open circuits inside. It produces a lot of energy to perform this test where a multimeter can't help.  Its more common for the field coils to be the problem, hence why most folks like 31 Caddy gambled to trying to rebuild this on his own. Armatures don't always go bad and when they do, its usually quite expensive (labor intensive) to repair an armature. If an armature is so rare, you may not have a choice.

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With the cutout not pulling in on it’s own when the RPM is increased from idle tells that there is no voltage coming out of the generator. I currently use a Peterson regulator in my 31’ Chevy but I’m trying to locate the gentleman that makes the regulators inside of cutout bodies so no alterations are needed to the generator. I do not want to remove the third brush and thermal switch out of my 32’ Olds generator.

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Growler is an electromagnetic device used for testing generators and starters, and it can also be used to recharge the magnets in a magneto. If you have a magneto with permanent magnet, or an alternator with permanent magnets as on some British motorcycles they gradually lose their strength but can be remagnetized with a growler.

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Sorry Rusty but no......a growler produces an alternating field which will neutralize a magnet.

A magnet can be magnetized using a DC current only.

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A growler will also hold 64 oz of your favorite brewed beverage from the local microbrewery, or at least that what I’ve been told 😀

Edited by TerryB (see edit history)

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My 29 Graham-Paige 827 with a Delco generator has a fuse screwed into the back, looks like a black valve stem cover.  If the fuse is blown you get nothing.

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If you unplug the growler while an object is in the magnetic field, it will impart a magnetic charge, but, you will not know what polarity it is until you check it. 50/50 chance to be correct polarity.😉

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