VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 36 Generator

Hi all, The generator on my 36 pickup is putting out 7&1/2 volts at idle and when the rpms are increased the voltage raises to about 12 volts. Is this too many volts? how much should it produce at say 40 to 50 mph? Any advise is appreciated. Thanks....Richard

6 or 12 volt system?
With the 6 V generator it should produce about 7.5 V. at speed - less at idle.The original 6 V
. gen.is a 3 brush with no type of voltage regulator.It would produce about 20 Amps at 50 MPH.

At 20 amps, the generator would be overcharging and the armature could throw solder with such a high output. A more safe charging rate would be around 12 to 14 amps at 50 MPH.

Hi all,
This type of generator has the field earthed via a resistor on the headlight switch.That is,when the lights are off,the resistor is in series with the field to earth,lowering the ouput of the generator.The total current output will still depend on the position of the movable third brush,and in most cases,it should be no closer than 2 commutator segments to the positive main brush.
This resistor was one of the first steps to provide some sort of "regulation" to the output of the standard third brush generator.If the field is not either connected directly to earth,or to the resistor(it may be burnt out),then the field system will be disconected.
As a third brush generator is self exciting,
this will lead to the generator output rising to the point where it will burn out the armature and the field coils,as the voltage produced on open circuit operation may reach 30-60 volts.The
result-a re-wind.
I recently had to rewind both the armature and fields for a '29 DA Dodge generator because of this.It was tested by a "professional" auto-electrician,but he did not have a 6 volt battery connected to the output side of the generator cutout,and it totally burnt both the fields and armature out.
So,if the resistor is burnt out,all you need to do is to run a heavy gauge wire from the field earth terminal post to one of the cutout mounting screws,and adjust the third brush accordingly like JYD suggests.

:)

Only the Master series used a resistor.The Standards and trucks did not and had a lower charging rate.

Charging rate on a 1936 truck.I was going by the 1938 shop manual as the trucks still had the old style generator.It was rated at 20 amps.I assumed that seeing the 1936 truck already had an air cooled generator it would also have the 20 amp rate.Did I assume wrong?

Hi Chev Nut,
If the generator is a standard non-ventilated type,the maximum output "cold" would be 18-20 amps,and the maximum output "hot" would be 12 amps.
Looking at a 1947 edition of "NASCO" Genuine Chevrolet & Maple Leaf Parts & Accessory book,the generator "earthing" resistor part no's are as follows:
0.75 Ohms 1934-39 DA,EA,GA,GB,GC,S,HL,13,14,15
16 (P/No. 817911)
1.05 Ohms 1934-39 DA,EA,GA,GB,GC,S,HL,13,14,15
16 (P/No. 810922)

I've re-built quite a few '36 generators,both passenger and commercial,and nearly all of them had a field earth terminal on the generator barrel beside the cutout,ventilated endplates and a fan that was separate to the pulley.Perhaps these generators were specifically meant to come "down under",but that's a debateable point I suppose.



:)

The 1936 specifications for the generator used on the Standard and truck models is as follows:

Model: 946-C (no headlight resistor)

Maximum Charging Rate, Cold: 15-17 Amps, 7.9 - 8.0 volts at 1,600 RPM.

Maximum Charging Rate, Hot: 11-13 Amps, 7.5 - 7.8 volts at 1,850 RPM.

Field Draw: 4.0 - 5.9 Amps at 6 volts.

For this application setting the third brush for a charging rate of 20 amps would be too much and eventually the armature will start to throw solder. Also, I have found, that in most of these applications when a headlight resistor is not used, the third brush should be set anywhere from 3 to 4 comm. bars distance from the main brush.

Hi everyone, thanks for the info as always. Well according to your information it looks like my gen. is ready for a rebuild. It registers 7.5 volts at idle and 15-16 volts at higher RPMS. I tried turning the voltage down but it will not go below 7.5 volts.....Richard

How are you testing your generator?

:confused: :confused: :confused:

Hi JYD, I tested it with a voltmeter....Richard

JYD, I should have said that I checked the generator with the red lead of the voltmeter at the cutout forward terminal and the black lead to the case....Richard

You probably need to have your generator output tested on a generator test bench to determine the actual condition of your generator.

I just had a go around with a three brush generator on a F----- . Was puting out 14 to 16 volts using a battery drill to turn it. Changed the armature to a spare I had and works fine now with about 7.5 volts at fast idle.