1929 Chevrolet Charging System, Electrical Concerns

Was doing an electrical check on my 1929 Chevrolet, to see what kind of voltage the Generator is putting out.

Concern 1

Battery is disconnected, and using a volt meter on DC. touch the ground to frame and then touch the positive to the output of the cutout switch (from cut out to battery) and get a reading of 5.4 volts ?? same reading if i touch it ground to frame and positive to starter.

-why would i have a volt reading ??

-where would it be coming from ??

with battery connected this reading matches what my volt reading is direct on the battery within a few tenths of a volt.

Concern 2

with battery connected and car running i am getting 8.5-8.9 volt reading on the generator side of generator. is this good, or ??

Does the generator put out a CONSTANT voltage and the third brush vary the CURRENT (AMP) output ??

I'll think on #1 and I'm sure others will have the answer.

DO NOT run the engine with the battery disconnected as the overvoltage can be damaging to anything electrical that is energized. One meaningful test for the generator is voltage at the battery an engine speed of at least 1200 rpm; the voltage should be 7 to 7.4, more or less.

OK, to clarify on Concern 1,

Battery is DISCONNECTED & Engine is NOT running !!

Yes I agree, that running engine with OUT the battery connected will cause harm, as the Generator TRIES to charge something that is NOT there...

With the engine off and not running, and all wires connected properly, there should be battery voltage on the battery side of the cutout, which it sounds like you have. Likewise, there should be zero volts on the generator side of the cutout. If you have any voltage other than zero on the generator side of the cutout with the engine not running, your cutout points are stuck closed and you should replace the cutout. With the engine running, there should be about 7.5 volts on either side of the cutout. If less, your points are open or damaged with a high impedance and you still should replace the cutout...

At first blush, if you are measuring on the battery side of the cutout, and the battery is disconnected from the cutout, there should be no voltage at the cutout. If the wire from the cutout to the battery is disconnect AT THE CUTOUT, and you measure at the end of the disconnected wire, you should measure battery voltage. You don't say where the battery wire was disconnected...

Even with the battery disconnected from the cutout, the starter switch is still connected to the battery and the wire that goes to the cutout is still connected to the starter and the battery.

Frank

Frank...

thanks for the insight. TO clarify the Battery was disconnected at the Battery POST (BOTH Pos & Neg) Cables were Disconnected from the Battery, same as if there was NO battery in the car at all. I will do a double check on myself and numbers tonight when i get home. just make sure i am not missing something.

ok, double checked my numbers.

With the Battery DISCONNECTED (BOTH CABLES) at the Terminals on Battery, i get NO reading on the meter from ground & positive on either side of generator or Starter.

With the GROUND CONNECTED to the Battery and the POSITIVE disconnected at the Terminal on Battery. I get the approx 5v reading at the Gen CutOut Battery side or at the Starter. Does this make sense ?? how do i get 5v with out the POSITIVE CONNECTED.

These readings are correct. Both points you measured are the same as the battery. Why do you think you have a problem?

Frank

Just read it again... With the pos battery disconnected, you cannot have 5 volts at those points...

First, is you car positive or negative ground?

Chevrolet = Negative Ground

OK, I think I have solved this one. There is a stealth path to ground created by battery acid, dirt and moisture connecting the negative terminal to the battery hold down and/or the battery tray. This path will not conduct much current but it doesn't need to has the voltmeter draws very little.

I will clean up the battery and do a recheck then advise

What you say makes complete sense

my 1929 chevrolet out puts 9 plus volts and 18 amps measured at the battery terminal on the cut out with the engine running, turning the adjusting screw seems to have no affect on the output. also is there a difference between a 1928 and a 1929 cutout ?

The 3rd brush in the generator regulates the generator output. The cut out is only a switch and is activated at 700 to 1,000 rpms. Get a 29 service/owners manual from the Filling Station. It will make your maintenance, adjustments, and repairs so much easier. The basic difference between a 28, and a 29 cut out is the orientation position where it is mounted on the generator. The 28 is crosswise, and the 29 is in line with the generator body. Many people have changed the internal components of their cut outs out to a large diode. When the cover is on the only one who will know is you. I have had cut outs stick closed and drained the battery. There are two manufacturers of actual regulators for these old generators. One fits into the band and the other replaces the internals of the cut out. Art

I put the electronic regulator (band type) on my 29 Cad and have never looked back. 

No more third brush to deal with.  It was always charging too strong or too weak.  I learned why so many service stations back then did so much battery repairs. 

On 5/26/2020 at 2:45 PM, m-mman said:

I put the electronic regulator (band type) on my 29 Cad and have never looked back. 

No more third brush to deal with.  It was always charging too strong or too weak.  I learned why so many service stations back then did so much battery repairs. 

That is the Peterson electronic regulator and mine also works perfectly. It reads the voltage in the battery and maintains the amount of charge it needs while driving. At daytime mine will drop to only a few amps after a long ride and will show about a constant 0 amps at night rather than showing a discharge like a standard generator and cut out. The Peterson regulator still needs a cutout or a diode.