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chstickl

37 Roadmaster Generator Polarization or other trouble?

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Last week my wife and I took our 80C for a tour through the Swiss Alps. At the beginning, I could still watch on the Ammeter that the generator was charging the battery and reacted to switching the light on or off. Then it stopped charging and we finished the week on battery power - not a solution for eternity. I checked the regulator, but could visually see no issue. Manually pressed on the relays while the engine was running, no reaction. Then I checked the generator and exchanged the worn down brushes with great hopes that I found the issue - what a disappointment. Did the usual tests:

- ground the F field terminal: no change, no charge, neither on idle, nor on high revs

- measure the voltage on A terminal with med to high revs: only 1V - 1.5V, independantly if F is grounded or not, so the cut-out relay does not open

- bridged the cut-out relay engine standing (is this what they call polarizing the generator?): no difference afterwards

I am at the end of my wisdom and fear that there might be a short or open connection somewhere inside the generator.

Would be grateful for any other idea or advice.

Thanks in advance, as always.

Chris

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post-51852-143142574153_thumb.jpg

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Check all the grounds and connections in all parts of the system. With engine off momentarily jump a wire from the BAT to the GEN or ARM terminal on the regulator. This polarizes the generator. Start the engine and run at fast idle, but less than 1800 RPM. Ground the F or Field terminal of the regulator. The ammeter should show charging and the battery voltage should be around 7 volts. If you do not see 7 volts, most likely the generator is not functioning and may need to be rebuilt or repaired. Once the generator is repaired try to obtain a new or rebuilt regulator. Polarize as described above and you should be OK.

Good luck.

Joe, BCA 33493

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Thanks Joe, as this is exactly what I did already, I have to presume that I need to get the generator repaired. As to the regulator: I still have the original regulator with the guard terminal for the starter switch. Non of the sources known to me seems to have replacements or rebuilt ones. Does anybody know a place where to get them?

Chris

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You can probably use a later regulator of the same ampere rating. The wire from the starter circuit to the "solenoid relay" was connected to the ARM or GEN terminal on the regulator. When the engine is not turning the generator armature is not turning either and the ARM or GEN terminal is at ground potential. With the ignition switch on and the accelerator depressed the solenoid coil will pull the points inside the solenoid relay closed to activate the starter. Once the engine starts the GEN or ARM terminal is no longer at ground potential so the solenoid relay cannot engage the starter.

My MOTORS Manual for 1935 to 1942 shows 1938-39 Buick generator has maximum output cold at 31 amperes.

I am certain that a later model regulator for a 30 ampere generator can be wired in to function properly.

Joe, BCA 33493

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Sounds like grounding the field terminal of the regulator proved you have a bad generator. Once repaired, if you end up getting a new regulator, here is the story (you can search on " '38 voltage regulator" for the entire thread:

I can believe that the change from 5 to 4 terminals may have been in the '38 model year - or shortly thereafter. It's such a simple difference, I am surprised there ever was a five terminal. The fifth terminal is labeled "IGN" and provides a reference voltage to the regulator during it's effort to begin regulating or restricting the generator's output. It was believed that the voltage at the IGN location under dash would be a better reference than using BAT, which, although it's the same approximate 6 - 7.5 V, has a different set of voltage drops in it's particular circuit. So, the two choices of reference voltage may differ by 0.1V or so. Later, they decided to use BAT, which is already brought to the voltage regulator and tied to the cutoff relay. A simple internal connection and BAT can also be used for the regulator coil, saving the extra lead and time to connect it. Bottom line - if you want to go from a 5 terminal to a 4 terminal, just leave the IGN lead off, and tape it carefully to be sure it never contacts ground. The connection is taken care of internally.

Now, the forth terminal is a different story. To engage your starter (with the accelerator pedal feature), you flip the ignition to "on", which provides voltage to one side of the switch at the carburetor. When you step on the pedal, this switch closes and provides the voltage to the relay on top of the starter. Here's the tricky part - the ground path for this relay goes to the regulator (terminal labeled GND) and through a set of normally closed contacts at the cutout relay, then on to the armature of the generator, through those windings, and ultimately through the field coil of the generator and to ground. Why? When the engine starts, the generator begins building up voltage, and the cutout relay changes state. The normally closed contacts open, which interrupts the ground path of the starter, keeping you from grinding the starter as the engine begins running. (Of course, at the same time, the normally open contacts close, allowing the generator to charge the battery.)

The other thing that happens in this system is the carb switch has a vacuum port, so vacuum will pull open these contacts when the engine begins to run.

Both of these work in parallel, to ensure you never engage the starter with the engine running.

If you want to go to a three terminal regulator, you have to account for this ground path for the starter. The quick way is to simply remove the GND wire from the old regulator and connect it directly to ground when installing the new regulator. BUT, if you do this, you will be defeating the redundancy originally designed into the system. If your vacuum pull-off fails to open the contacts at the carb switch, you will be energizing the starter whenever you step on the gas, as you drive the car! Very bad. Carbs do tend to gum up over time.

Better - take the ground wire and splice a lead to it. Run the lead through the firewall and to a push button switch, then to ground. In this way, you will use the push button to ground the starter relay, and the carb switch to provide power.

Alternate - Just ground the wire to the base of the new regulator, and take the carb switch leads back through the firewall to your push button. Now you are switching the "high side" of the circuit with the push button, with the low side permanently grounded.

Your choice. I went with the first option, because it would be easier to go back to a four terminal, if I find one. Plus, you can still demonstrate the pedal start feature.

Pretty cool, huh?

Jeff

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Jeff:

From reading your post above, it seems the 4 terminal regulator had an additional set of contacts on the cut-out relay that were normally closed. Then when the generator started to build voltage in the armature above the battery voltage, this set of contacts opened as the regular cutout contacts closed. Do I understand this correctly?

Joe, BCA 33493

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