Generator full field test by Paul m. Anton

Here's what the generator circuit looks like.

The regulator grounds the field for full output and inserts a resistance for minumum output.

If you will put an alligator clip lead to the generator field terminal and ground AND connect a voltmeter directly to the generator load terminal you can quickly test the system. Run the voltmeter leads under the cowl into the cockpit.

Now run the engine up.

Ammeter reads charge --> trouble in the field wiring or regulator.

Ammeter reads no charge but voltmeter shows increase of voltage --> trouble in the generator output circuitry---open wiring---bad generator fuse holder ( I just fixed one of these in a Coupe)---etc.

Ammeter reads no charge --> voltmeter never shows output --> bad generator.

If the full field test shows the generator is OK then remove the alligator lead from the generator field lead and connect it to the field lead at the regulator itself. If you have output the regulator is bad. (make sure it is making a good ground)

If this test does not result in full output, then you can try it at the master switch making sure you have the correct terminals since grounding the battery side will make for fire and smoke.If grounding the field at the switch itself does not give output than you can look for bad wiring between the generator field terminal and the switch.

Here's what the wiring diagram for the regulator looks like


Paul N1431A KPLU

Type certificate data sheet No. E-233 covers basically all of the C-75 and C-85 engines. Note 3 of the TCDS lists Four generators as being eligible for use on these engines.

We usually talk about the Delco-Remy generator no. 1101876 as being a 12V, 13amp generator and in AC 43.13-1B par.11-33 we limit the output of the generator to 80% of it's rated capacity.

The TCDS lists the 1101876 generator as being a 15A unit, not 13amps and the 80% limit would therefore be 12 amps. I had been a bit confused and figured that the 80% would be taken from the 13amp figure instead of 15amps.

The other generators and amperage listed are: NO. 1101890, 20amps; 1101879, 25amps; and the 1101898, 35amps. Another interesting fact is the weight of each generator. The 1101876 and the 1101890 both weigh in at 10 lb. with the 1101879 at 14 lb. and the 1101898 at 16 lb..

Rich Blair

Page last modified on January 31, 2010, at 12:53 AM