The Stovebolt Site Forums The Shop Area The Electrical Bay '37 PU charging system

My '37 "ran when I parked it" about 10 years ago. I am now getting into a restoration. To start it I used to pull the interior light switch into the central location, get it running and then pull the switch out further to charge the battery, and even further to get head lights. I was told to watch the ammeter and not overcharge the battery. Now that I am doing research and reading this site, I have learned that the generator has a cut-out mounted on it. What does this do?
I am going to have the generator rebuilt, should I have this cut-out rebuilt too?
If I have this cut-out, why do I have what looks like a regulator mounted on the fire wall? It has what looks like only 2 switches vs. the three that I normally see.
Is this a standard set-up or has it been bastardized? What do I do to get back to original as I want to keep this 6 volt system.
I thank you each in advance for the help. I have learned a great deal from you all!

CAB

You're describing a 3-brush generator with a cutout relay and resistors mounted to the headlight switch to increase generator output while using the headlights. The cutout relay keeps the battery from discharging itself through the generator when the engine stops. I've got some Delco-Remy technical bulletins covering that system that I can scan and copy if you're interested in keeping it original. For simplicity of operation and reliability, I'd suggest swapping to a later model 2-brush generator with a 3-unit regulator, but staying with the 6 Volt electrical system. The only reason to stay with the original system is if you're doing a totally original restoration. The old 3-brush generators did a really lousy job of keeping the battery charged. It's easy to adapt the system to a slightly more modern setup.
Jerry

I second what Jerry is suggesting. It was really a poor system. My 38 Master already had the more modern 6 v generator setup on it but I will be installing a 12 volt generator. I am doing this because I can get very bright headlight bulbs (Ron Francais bulbs) that are the same size and shape of the originals. At the same time I will be installing electric wipers.

Jerry:

I am not trying for totally original, only keeping the 6 volt. What's involved in changing to a 2 brush generator and regulator. Electricity is not my "thing" but I like the idea of simple and reliable operation. What do I do with the old generator? Where do I get a correct one that will fit? How do I wire a new regulator and guages?
Thanks for the advice and input.

CAB

A post in the "parts wanted" section of this site will probably get you in touch with someone who has converted his electrical system to a 12 volt/alternator setup. Some of us collect obsolete parts, so it's not impossible to find serviceable takeoff units for the conversion. Making the older system available to someone who is doing an original restoration will probably bring in a little pocket change for you, also. I believe the 2-brush system with the 3-unit regulator was used from the early 1940's through early 1955, so the parts aren't particularly scarce. Virtually all General Motors vehicles, cars and trucks, used similar parts, so you're not necessarily limited to Chevrolet truck items.

There's probably room on the firewall or one of the inner fenders to mount the regulator. Connecting the system involves running a couple of wires from the regulator to the generator, and one from the regulator to the ammeter. I can provide a wiring diagram for the system if you need it.
Jerry

You can mount the new regulator where the old one was mounted.

Christopher,

Many of the three brush generators can be run just fine by replacing the cutout with a voltage regulator. Additionally, on many three brush generators, the output of the generator can be adjusted by moving the third brush. The third brush is mounted on a slide for this purpose. The point of this was to set the generator output for the type of driving you did. For a lot of stop and go, the generator would be set to high output to keep the battery charged. If you did a lot of daytime long distance driving, the current output would be set low so as to not over charge the battery.

The cutout does not control the amount of current the generator produces, whereby a voltage regulator will. So to use the generator with a voltage regulator, the third brush can be moved to produce max current and the regulator will control the output.

Main thing is if you want to move the brush all the way over you will want to know what the max safe amperage the generator can produce so you can match it up with the right voltage regulator. Or just keep the brush where it is and use a standard 6v regulator.

I'm a fan of keeping all the original equipment you can. So even if you replace the genny and cutout, don't toss it. The next owner may really appreciate having it.

Kurt

Most 3-brush generators don't have enough current capacity to benefit from trying to use a 3-unit regulator. There's a reason GM didn't just decide to design a new regulator, instead of developing a complete new system. Moving the third brush in the direction of rotation increases the output, so if you decide to do it halfway and overload the old generator, max out the brush movement as far as it will go and set the current regulator to a fairly low reading, 20 amps or so. It makes no sense to do that when there are balanced systems available with the right generator included.
Jerry

Jerry,

Actually it was in 1937 when Chevy made available the voltage regulator in lieu of the cutout relay, and what they did was to basically use the same 3 brush generator, but fixed the third brush in the max current position. The generator would produce 20 amps or more.

Here is a link to the 1937 Chevrolet Service News:
Voltage regulator generator

Just for fun, here is the service news bulletin about how to control charging rate with the resistor in the light switch:

How to increase generator output
So anyway, depending upon which generator he has, it might work just fine. I think I would try it, but see if the generator gets too hot, in which case I would back off on the brush.

Sure is interesting stuff. LOL I enjoy these "sparks" discussions.

Kurt

Thank you all for the insight. Since this old girl has beenrunning fine for 75 years, and will now only be used for weekend runs, I think I'll try to keep the old generator/charging system. When I get up and running, what will gauge if the generator is getting too hot? I am sure it gets warm from the engine so is "hot to the touch" a gauge?
Thanks again to all. This site certainly has helped me.

CAB

Christopher,

If you are going the voltage regulater route, You might try finding out the rated capacity of the generator, and then have the rebuild shop set the third brush so the generator will not exceed that output. Do you have the number from the genny plate? There is a lot of data out there about generators, and having that number would be the key.

Otherwise have the rebuild shop do there thing and get another cutout.

Kurt

Kurt:

The plate on the generator reads:
Anderson Ind.
Delco Remy
948R 778660
Model Serial

Does that add to the picture?

Another thing I don't understand is that if the gererator has a cutout mounted on it, why is there what looks like a regulator on the engine side of firewall? The "regulator" has two switches and two what look like fuses. Is this a backup to the cut out?

Thanks again.

CAB

It sounds like you've got parts of two different systems installed. Can you take some pictures and send them to my email? The generator with the cutout relay mounted on top of it should not have an external regulator, and the 2-unit regulator that was the next step in the process had its own cutout relay, plus a voltage regulator- - - -no separate current control. The system I'm referring to as an upgrade has a 2-brush generator and a 3-unit regulator. The regulator has a cutout relay, a current regulator, and a voltage regulator. It's designed to work with a generator capable of producing about 30-35 amps, considerably more than the 3-brush unit. PM me if you can't find my email address on my profile page- - - -I don't remember if it's still there or not.
Jerry

CAB,

I believe that the 948R is the original generator for your truck. I have an old Army maintenance manual from about 1944 that indicates that the 948 R would put out around 20 amps at 8.4 volts at 2800 rpm when hot. This would be with the field terminal grounded.

The third brush setting is what limits the max current output because it controls the max field strength of the generator. Since 20 amps is the rated max output, it is important that the generator's 3rd brush be set so that this output cannot be exceeded. A good generator shop can do this for you.

Anyway, you should then be able to use a more modern voltage regulator to control the charge rate of the generator because the vibrator that controls the field strength will reduce the current output as the battery voltage comes up, but will not be able to cause the current rating of the generator to be exceeded because the third brush setting limits the max current output.

So if a 20 amp generator meets your power requirements, you should be fine. A bit of rewiring will be needed as you will no longer want the light switch resistors in the circuit. There is no guarantee that this will work as well or as efficiently as a two brush generator and matched voltage regulator, but it should work.

I can email you this army tech manual if you like. It is very cool and has an excellent explanation of how all this works.

I don't imagine that you have two cutouts connected to your generator, so I'm thinking that either one is disconnected, or one of them is something else. If you study it carefully with VOM in hand, you should be able to noodle it out. A picture would be helpful as Jerry suggested. If you don't have a photo hosting account somewhere, I could host the picture for you on my server so you can post it to the board.

Kurt

Kurt and Jerry:
Thanks for the input. I have not digested it all, yet. I'll try to get pictures this PM and then figure out how to post them. I'll also try to follow the wiring to and from the regulator.
Thanks again. I'll be back to you ASAP.

CAB

Kurt and Jerry:

Here are pictures of what is on the truck:

http://s1254.photobucket.com/albums/hh614/CAB502/?action=view&current=77729cf6.jpg
http://s1254.photobucket.com/albums/hh614/CAB502/?action=view&current=600e7840.jpg

What do you think I have?

Thanks,

CAB

Christopher,

First of all, it looks like the cutout on the generator is not hooked up.

Secondly, it looks to me like you might actually have the early voltage regulator already installed. I am not familiar with what they look like, but according to

This:

Diagram the original voltage regulator unit released in '37 as an upgrade did have four terminals and two contacts, with the voltage regulator portion having two coils operating one of the contacts.The other contact is the cutout. Note that the regulator is controlling a three brush generator.

Would be interesting to see a picture from the side of the unit. Have you traced the wires to see how it is hooked up? Is it hooked up the same way as shown in the service news info?

What do you think, Jerry?

Kurt

The 2-unit item on the firewall with the fuses is a headlight relay- - - -one set of contacts for high beam, the other for low beam. It has nothing to do with the charging system. That was a very popular aftermarket add-on for 6V headlights because it took a lot of voltage drop out of the circuit and resulted in brighter lights.

The wiring on the cutout relay looks a little flaky as well. I'll have to do some research in my tech bulletins to see if there's a circuit diagram for a cutout relay equipped 3-brush system- - - -but I believe I have one that also includes the circuit for the output boost through the headlight switch.

The only way I'd spend a lot of time and effort on that system would be if I was doing a 100% original restoration. The 2-brush generator with the 3-unit regulator is a far better system, and not that expensive to convert.
Jerry