Generator Internal/External Grounded?

[Lloyd]

I am instaling a rebuilt generator and NOS regulator on my 39 Plymouth. My manual states that there are two different methods to polarize the generator depending on if the generator is internally or externally grounded.

 

External - Touch a jumper wire between armature and battery terminals on the regulator.

Internal - Disconnect field terminal connection from regulator then touch the field terminal lead to the battery terminal at the regulator.

 

So how do I tell if my generator is internal or external ground?

Edited August 23, 2015 by Lloyd

[Plymouthy Adams]

your generator body and regulator base share common ground...is this what you asking..

[Lloyd]

The Motors manual says if the generator field is grounded internally or externally.

I've read thru posts about polarizing and everyone states the first method - touching a jumper wire between the armature and battery terminals on the regulator, which would be the method for an externally grounded field.

Havnt seen any posts which even mention the method for an intenally grounded generator.

Edited August 23, 2015 by Lloyd

[Plymouthy Adams]

field should not be grounded to the chassis...function of the regulator...the book specifically has a test to ensure field is not touching generator body and thus grounding

[TodFitch]

Whoever rebuilt your generator should have tested it. And if they tested it, it should be polarized already.

 

Maybe they polarized it in reverse of what you need, but if it were me I'd just bolt it on and see if it works. If not then I'd worry about polarizing it.

[Lloyd]

I did test it, ran the engine briefly and the amp gauge did not appear to be working.

So I'm wondering if I need to polarize the generator.

[Don Coatney]

Polarize it and try it.

 

[Lloyd]

I went ahead and polarized the generator then started the engine. Pulled a battery cable and the engine kept running so the generator has to be working. But the amp meter still does not register. Checked voltage at the gauge and its getting 6 volts both terminals.

Both fuel gauge and amp meter I got off eBay - NOS. The fuel gauge was not working either, I just connected the original fuel gauge and it works. So the NOS gauge has a problem.

I'm guessing the NOS amp meter has a problem as well. Tomorrow I'll swap that back to the original and find out.

If nothing else I did get new gauge faces..

[Jocko_51_B3B]

 

    Difference Between Externally Grounded and Internally Grounded Generators

 

Generators are classified as Type A or Type B.

 

For Type A generators, the field current (and thus the output voltage) is controlled by rapidly vibrating (opening and closing) voltage regulator contacts inside the voltage regulator. These vibrating contacts provide intermittent grounding for the field windings. Because these contacts provide ground for the field windings from outside the generator itself, this type of generator is called an external ground (Type-A) generator.

 

For Type-B generators, the field current is also provided by rapidly vibrating contacts inside the voltage regulator, but in this case, these contacts do not provide ground. Instead, they sample the generator output. The field windings are grounded inside the generator so this type of generator is referred to as an internal ground (Type-B) generator.

 

 

 

         Type A - External Ground                 Type B - Internal Ground

 

 

 

The diagram below comes from the 1951 Dodge Truck Shop Manual on page 208. The generator ( labeled #12) in the diagram matches Circuit A above. So, the generators in Pilothouse Trucks are  Externally Grounded.

 

 

 

 

 

How to Polarize a Pilothouse Generator

 

To polarize an "A" circuit generator (external ground), momentarily connect a jumper lead between the regulator BATTERY and ARMATURE terminals after all leads have been connected, but before the engine is started. (This is how a Pilothouse Generator should be polarized!)

 

To polarize an "B" circuit generator (internal ground), disconnect the lead from the regulator FIELD terminal, and momentarily touch the lead to the regulator BATTERY terminal. This should be done after all other leads have been connected and before the engine is started.  (Pilothouse Trucks are not polarized this way!)

 

 

 

A Goes With A   and   B Goes With B

 

Another thing to remember is that generators AND voltage regulators are classified as either Type-A or Type-B. They must match. If you have a Type-A generator, then you must use a Type-A regulator. Type-B regulators are only for Type-B generators also.

 

 

 

A Way to Check Whether a Generator is Type-A or Type-B...

 

I wanted to prove for my own satisfaction that my B3B generator is externally grounded (Type-A). So, using the Type A and Type B diagrams above as guides, I measured the resistance between terminals A and F and compared it to the resistance measured between F and ground (which I call G) on the generator case. Here's how I decided if my generator is Type-A or Type-B:

 

If the generator is externally grounded (Type A), then the resistance measured between terminals A and F should be less than the resistance from F to ground (the generator case).

 

If the generator is internally grounded (Type B), then the resistance measured between terminals A and F should be greater than the resistance from F to ground (the generator case).

 

Why should this test work? Because for Circuit A (External Ground) the ohmmeter current from A to F only goes through the field windings, whereas current from F to G goes through the field windings AND the armature windings. The reverse is true for Type-B).

 

For my generator, (A to F) was 3.6 Ohms and (F to G) was 3.9 Ohms which tells me that my generator is externally grounded which agrees with the diagram from the Dodge shop manual.

 

(Information above was taken from http://www.bowersflybaby.com/tech/delco_remy_generator.pdf and the Dodge B-3 Shop Manual.)

 

 

 

Edited March 7, 2020 by Jocko_51_B3B
Added information and clearer explanation.