VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1929 Generator Charge Setting

The 1929 service manual does not give specific voltage readings or charging rates. Not sure if the amp meter is calibrated in amps, or if the scale is in some arbitrary units. At about 2000 RPM I am reading 20 on the amp meter and showing about 8 volts at the battery. I feel that is a little high, but what should I be reading? The service manual just says to adjust the generator to charge a little more in winter than in summer. What would be a normal reading on the amp meter, or a volt meter, with lights on? Lights off? At what RPM? For summer? For winter?

The voltage is about right, but with all lights off, the current seems too high. Have you checked your battery fluid level. If it is overcharging, the water will boil off too fast.

Smarter folk than me will chime in here and give you the best valuse.

Sustained charging at over 12 amps on an unventilated generator risks overheating. Pre-35 generators are unventilated. If overheated the armature solder will melt destroying it. Unless you run headlights there is no need to have the generator output above 6-8 amps. If you intended to do much night (or winter) driving then 10-12 amps should be your setting.

I was surprised to find that the power to start the engine was restored by a generator in a '28 Chevy set at ~8 amps within 3-4 miles. After that you are overcharging which boils out water and lowers battery life.

20 amps output is way too high! You are going to do some major solder throwing eventually. At 1,700 RPM (generator speed) a safe output would be 8.5 volts at 12 amps max. As Chippy Dippy said you can set the output down to 6 or 8 amps if you are not using your headlights.

Hmm, I think mine is high too. time for a check.

Thanks for the feed back. Now I have some numbers to work with. Am I right to assume that setting the output of the generator only changes the current it puts out, but not the voltage? Or does reducing the current also reduce the voltage?

You also need to check the voltage that the cut-out contacts close at,as this will also affect both charging current & voltage.The nominal closing voltage for the cut-out contacts is between 7.0 - 7.5 volts.The air gap for the moving arm contact is 0.020" with the moving & fixed contacts just touching.
Also when checking the output of your generator,you must use an accurate ammeter connected in series with the output terminal of the dutout,and the lead that goes up to your ammeter to get an accurate current output reading.Don't rely on the ammeter on the dash,as they are not an accurate indicator,and you have to take ignition current draw into acount.

So i did some searching and could not find any details here on adjusting the generator. I know you have to move the brush, but does anyone have any pictures? I for one need to adjust ASAP.

If you have a copy of the 1927/1928 Capitol AA/National AB
repair manual,it should have pictures and a explanation of how to lower or raise the charging rate.But if you haven't,this is how to do it:

Remove the cover band from the generator casing(it clips on),
and locate the small round head of the third brush locking clamp plate screw on the commutator endplate.with the engine idling,loosen the screw just enough to enable you to move the third brush arm.This arm is located between the positive main brush,and the negative main brush.To increase the charging rate,move the third brush in the direction that the armature is turning(anti-clockwise looking at the commutator end)toward the positive main brush(this is the brush that is connected to one side of the cutout),until you get your desired charging rate.But you must not move the thid brush any closer to the positive main brush than 2 commutator segments,or you will risk burning the generator out.Then tighten the clamp screw.
To lower the charging rate,simply move the third brush arm against the direction of rotation(clockwise at the commutator end)until you get the charge rate you require.Then,as above,tighten the clamp screw,and replace the cover band.

This information on how to adjust the generator output is also given in your shop manual.

Thanks CJP. And for the record, I did check my repair manual and it does not provide the details to adjust, but I did find a page with voltage and current specs @RPM. And the owners manual says it can be adjusted by moving the brush and it should be left to a pro.

The 1929, 1930, 1931 and 1932 shop manuals all state the following:

CHANGING GENERATOR CHARGING RATE:

"When the generator output is insufficient to keep the battery in a fully charged condition and also supply current for ignition, it is necessary to increase the generator output by shifting the brush in the direction of rotation of the armature."

"Fig. 167 illustrates the method of shifting generator brushes in order to either increase or decrease the charging rate, as required."

"Figure 167" is a very detailed view of the back of the generator showing the third brush and how it is rotated. The screw that holds the third brush in position is also shown in the illustration with a screw driver in the slot. There are also many more pages in the shop manual that describes, in detail, the operation of the generator and the various tests that can be peformed to check out the generator.

As CJP'S 29 suggested, the 1928 shop manual should have the same information. However, I don't have a 1928 shop manual so I couldn't refer to that document to see what it states regarding the generator output adjustment.

We seem to be referring to different books. My repair manual is definitely not the same. Looks like i need to go shopping for a shop manual. It's no wonder i am frustrated with the book I have.

Again thanks for all the help.

Actually, the "shop" manual and the "repair" manual that we are referring to is one in the same, just different terminology is used. The actual name of the shop (repair) manual is: "Chevrolet Repair Manual". The face of the cover also lists the series of the vehicle and the effective date of the publication.

You can get reprint of the 1928 "Chevrolet Repair Manual" from the Filling Station.

And below that mine says: Showing short cuts and methods fir repairing Chevrolet Capitol and National cars.

But my fig. 167 show the use of a "growler" to test the armature.

My brain hurts...

It says the same on the cover of my repair manuals as well.

Since each year manual is slightly different each figure number is going to be different also. The "Figure 167" referenced above is from the 1929 "Chevrolet Repair Manual".

Look under "generator tests" in the electrical section of the index and see what you find.

OK, now i feel better. After flipping through the pages, two were stuck together and there was a cross section of the three brushes, but the explanation is nowhere near as clear as what CJ provided. Again thanks for edumakating me.

You bet.