The Stovebolt Site Forums The Shop Area The Electrical Bay '37 6 volt generator hook ups

The post with the nut not on the cut out switch.Am I right that is the wire on the diagram that runs to the light switch that is marked field resistance?Is the stud on the switch with the thin wire coil the other connection point?Also can you explain the term field resistance.Book mention it but no expaination.Thank You in advance !

ptc1937chevy,

I will preface this by saying I know nothing about this three brush generator. I did look at several pictures and it sounds like you have it figured out.

I have enclosed a link to a page of wiring diagrams. If you click on the '37 car or truck schematic (both the same), it shows the wire connections.

I went to a antique tractor site and there was a short explanation of the "field resistance" setup.

Generator current output is regulated by how much ground the field sees. When the headlights are switched on, more current is required. Switching the headlights on takes the resistor out of the field circuit and tell the generator to get with the program.

To fine tune the charge rate of the 6 volt battery, this resistor can be changed. A smaller resistor give a higher charge rate while a larger one results in a lower rate.

This is how I think it works...I could be completely out in left field. The nice thing about the Stovebolt is that folks aren't afraid to tell you that you're OTL, and enlighten you to the real scoop...sort of like going to high school all over again.


PS. Headed to Sacto from Eureka in the AM.


http://chevy.tocmp.com/chevywiring/index.htm

Stuart

The light switch has a resistor that reduces the field current which reduces the charging current your third brush generator puts out. When the light switch is pulled out, the resistor is shorted out and the field is grounded, causing the generator to go to full charge.

I installed an 8 volt batt in my 37 Chevy and the generator is now putting out 11+ volts. When we put the generator on the bench it only put out 7.2 and when I reinstalled the 6 volt batt in the car it only charged 7.2. Does any one know what my problem is or how to correct it?

Goldengoose007,

Welcome to the Stovebolt. Although I'm a green pea when it comes to these third brush units, I have read the only way to change the output voltage of the generator was to move the location of the third brush on the commutator.

Are you sure your volatge readings were good. Without physically adjusting something, one would think the system was reacting to the voltage of the connected battery....I don't know if this is possible. Maybe someone else has seen this!


Stuart

Dave,

From what you wrote, I can't tell if you have problem. I do think that 8 volt batteries are for tractors and are absolutely unneccessary in early vehicles as long as they are maintained. Eleven Volts sounds about right for charging an eight Volt, but it will significantly shorten the life of your light bulbs. What was the setup when you bench tested the generator? Was it tested with a six Volt battery?

The three brush system doesn't use a voltage regulator..but merely a voltage cutout relay. If a 8 volt battery were installed, wouldn't the field windings have higher voltage available to them, which in turn would allow the generator to produce a higher voltage.

The system is so primative that maybe it can be regulated by the voltage of the battery. Does this theory hold any water?

Stuart

An 8 volt battery is not necessary if your system has clean connections and at least a 2-00 positive and ground cables. Once you get that done, you adjust the third brush on the generator to 0 amps on the amp meter at idle with the lights and heater blower on. You should have around 7.5 volts on the output of the generator.
I am using a 6 volt Optima battery in my '36 GMC and have not had problem one.

You will not normally have any charging at slow idle with a generator, no matter where the third brush is set. The charging rate should be set at about 12 mph in high gear, not at idle, IIRC. I just have a cheapo tractor six volt in my 33 sedan and have no trouble starting when it sits for a month, though it is best to prime the carb because todays volatile fuels evaporate in the bowl.

Thank you for your answers. I also have a 1946 Pick up with an 8 volt batt that I've been runing for 4 years now. The major difference is that I have a regulater on it instead of a cut out. I think that will be my next move