PE-75-AF small genset problem

[Carla]

Hello, all,

This PE-75 is an approximately 1952 or '53 vintage belt drive unit, with a Briggs and Stratton engine, and 2.5 KW rated Kurz and Root generator.

We've gotten the engine running and the set belted up. It seems to run reasonably well, and turn the generator end at its desired 1800 or very nearly so, but now we've a problem.

The generator seems 'dead' when running, with no voltage readable anywhere on the terminals, wiring, brushes, etc.

i vaguely remember someone telling me that a generator of that type requires some residual magnetism, and that the magnetism will have dissipated if the unit was in dead storage for many years time.

If I remember correctly, I was told that it would be necessary to 'flash' some points in the wiring with low-voltage DC, as from a 6V battery, as with 'polarizing' an automotive generator.

Has anyone had experience with these, and could tell me whether this is so, and, if it is, to what wiring points or terminals should I apply the wires from the 6V battery? (or would 12V or 24V be necessary?)

I understand that the nominal 110 or 115VAC is between the two wires from the genset, and, unlike power co. wiring, there is no 'neutral', so each wire would be 55V to ground, meaning that the genset frame itself requires a safety ground stake, and any load driven from it must have its case or frame tied to a safety ground.

We couldn't read any voltage at any of the exposed terminals within the generator with the gen turning at apx 1800, its nominal speed per the manual.

If I'm mistaken about 'flashing' or 'polarizing' the generator with low voltage DC, then what might be the possible causes for no voltage at speed?

The generator has been stored under cover, and is generally clean. It appears to be in very good condition, per visual inspection, with no noticeable damaged, burned or perished wiring or parts. The brushes and brush springs seem to be in good condition, and the brushes seem to be making good contact.

cheers

Carla

[K D Redd]

Apply your DC to the brushs. I worked on a 20 KW Generac, Genejunk?, which I had to flash after correctly wiring in the regulator even though the owner, who knew little about a genetator, had boot strapped 12 volts directly from the units battery to the brushs causing it to generate about one half it's rated voltage. I was surprised the generator had to be flashed.

Kent

[rooster101]

One thing to do is to put a diode on the positive side of the battery leads to stop back feed, just to be on the safe side.

[Elden DuRand]

Carla:

When flashing the exciter (the part of the generator that has brushes working on a commutator........NOT SLIPRINGS), when running you only need to connect the battery for a second or less.

The output should rise when the battery is connected and stay up after flashing. You most likely won't have to flash it unless it sits for a very long time.

Take care - Elden
http://www.oldengine.org/members/durand/

[Robert Haus]

I have one from 1943 that had only about 6 volts of output when I first got it going....turns out the slip rings were dirty......once I got them cleaned up, the voltage came right on up to where it should be.

These are really good little sets! ....does yours still have the wood carrying handles stored in the sides of the frame? ....they go in the holes at each corner so 4 troops could carry them around!

[Rick Harvey]

Hi Carla
I had one of those 66-68 in the Air Force. Yes you have to flash the field. 6 or 12 volts should work. Just a momentary pulse provably would do it. That brings back memories.

Thank You
Rick Harvey
USAF Electrical Power Production 54350