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'38 voltage regulators


jeff

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Just wondering what everyone's experiences are with their pre-war voltage regulators. My '38 is supposed to have a five terminal, but has always run with a four terminal. Until this weekend that is, now I have a three terminal installed. Over the years, I have picked up a number of regulators at swap meets, so I have five, four and now a three terminal on the shelf, unfortunately, only the three terminal is working correctly. I have worked through the differences between them, and now understand the impact to the wiring harness for each.

Fives seem impossible to find, fours are difficult and threes are common. Have most folks made this transition, or are you still running with five terminal regulators?

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The good news is that you will have no problem finding a replacement, if needed.

Do you still have the gas pedal start feature, or are you now equipped with a push button start? If you still have the gas pedal start function, I think you are living with one less level of redundancy in the starter circuit than originally intended. The original arrangement had a vacuum pull-off function to open the carb switch when the engine started, plus the cut-out relay in the regulator opened a set of contacts to disconnect the starter relay from ground. So, you really had two switches, both making sure you could not engage the starter with the engine running.

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  • 3 weeks later...

Jeff,

My five terminal regulator just died two weeks back and has been replaced with a four terminal one I got off the internet [NOS still in its box!]. We were a little worried about condition after all these years but it was given the ok by the autoelectrician and the car is charging nicely. The regulator even still had its 'conversion guide' on how to move from 5 to 4 terminals. Yes it was hard to find but not nearly as hard to find as the 5 terminal one [which I am yet to find].

I had understood that the move to 4 terminal was an upgrade by delco done whilst the 38 model was still in production or shortly thereafter? That would certainly explain scarcity of the 5.

Mark - I lost the pedal start ages ago I suspect - its not been there as long as I have had the car - just a push button. How difficult is it to reinstall if I wanted to do that?

Regards

DT

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David,

It takes less than an hour. Slice a section of radiator hose to match the width of the pedal. Punch or burn holes in it to match the ones in the throttle rod and foot pedal. The throttle rod length can be adjusted on the top end, so mount the other end very close to the pedal. Attach the rubber to the rod first, and get under the car to attach the rubber to the pedal.

Provided your vacuum switch is still functional, you can eliminate your starter button. You should also be able to start the car with the throttle knob on the far left side of the dash.

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DT,

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?

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Guest Tishabet

Wow, Jeff, very good writeup.

I am currently running a 5 terminal with a push button starter. If I am hearing you right, I could use a generic three terminal starter by simply taping off the IGN lead entirely, connecting the GRD to any good ground and simply connect the remaining three wires to their labeled terminals on the three terminal model?

Since I am not using the throttle starter, the end result would be the same functionality I have today, yes? Just trying to make sure I understand.

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Yes, you should be fine. Opens up a whole new world of regulator availability, doesn't it?

Just confirm one thing before you start...

It sounds like somebody replaced the carb switch with a pushbutton switch on the dash. With the ignition on, but the pushbutton NOT pushed, take a voltmeter and confirm that you do not have voltage at either starter relay terminal (the small terminals, not the big ones). This will verify that your pushbutton switch is on the high side and not the low side (ground side) of the relay. If it was directly substituted for the carb switch, it will be on the high side. It will work either way, but I think the high side is preferred to keep a ground fault from causing the starter to run. (if you are switching on the low side, the regulator contacts are giving you a second chance to open the path to ground - so you may want to keep them)

Once you are sure of this high side switching, go ahead and permanently ground the GND terminal of your regulator.

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Guest Tishabet

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jeff</div><div class="ubbcode-body">Opens up a whole new world of regulator availability, doesn't it?</div></div>

Indeed! Thanks for the insights Jeff!

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  • 2 months later...

The change over is not difficult; if you have a 5 terminal regulator and wish to change it over to a three terminal regulator and keep your throttle start circuit intact with all the same level of protection do the following: tape the wire that went to the ignition terminal, connect the wire that went to the ground terminal to the generator terminal, connect the remaining three wires to the same respective terminals as they were before. The start solenoid relay will now ground through the armature of the generator, when the generator output reaces 6 volts there will be no difference of potential on either side of the relay coil, hence no current flow. This is the same circuit as used in 1939.

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