One-Wire Generator

No, that is not a typo, this gadget truly is a one-wire generator.

I have several old generators (thanks ORBill) that I am finally getting around to testing. This unit is a third-brush type and has no provisions whatsoever for controlling the field current; a quick google search for the part number 943U shows that it is for a 1931-34 Studebaker. Some further searching led me to a Studebaker forum where I found schematics that clearly show this generator having only one wire leading from the armature to the cutout relay.

The amazing thing is that it actually works! I realize that I am probably the last person on earth to learn that this was at one time state of the art technology, but I have always been a bit slow on the uptake

8 Volts at ~8 amps

My high tech generator test bench

steve(ill) wrote: never heard of one wire gen ...

Reckon I ain't never heerd'a sech neither But thar 'tis, right at the bottom of the diagram. The third brush picks off the field current from the armature, and the circuit is completed inside the generator by being grounded through the thermostat gizmo.

Whereas our familiar Allis-Chalmers charging systems give us the choice of manually selecting a high charge of ~10 Amps or a low charge rate of ~3 Amps, this unit simply provides a fixed charging rate of ~8 Amps depending on where the third brush is adjusted. The only other control is the thermostat which I presume to break the field circuit if it gets too hot.

When you are working on vintage machinery, it adds to the fun when you have vintage test equipment with which to do the testing.

This SUN VAT-60 automotive meter was in my late Father-in-law's shop when it was purchased from the long-time proprietor, Chas. Wallace of Careywood, Idaho. The ammeter was non-functional but the voltmeter still worked fine. I opened it up and and found the ammeter switch was bad which turned out to be an easy fix.

A bit of google searching revealed some newer versions of the VAT-60 but they have more modern digital readouts rather than the old analog units on this one.

Just for grins I decided to test the SUN meter against my Fluke 88, so I set it up checking the one-wire generator output with the Allis-Chalmers meter, the SUN meter, and the Fluke meter all in series so as to compare the readings simultaneously.

The Allis-Chalmers meter was a bit optimistic at ~7 Amps, The SUN meter read ~4.5 Amps, and the Fluke reads right at 4.15 Amps.

Not bad for test equipment that hasn't been used for more than 60 years.

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