I'm trying to understand how voltage regulators for DC generators are wired.

I'm working with a GE 44 whose auxiliary generator voltage regulators have been replaced several times over the years. The original diagram, and the current situation, both have regulators with fundamentally three connections: A+, F+, and A- (which doubles as F-). I'm sorry I don't have a picture to draw, but each unit is currently wired as follows:

1. Battery Positive.

2. A power diode (to prevent reverse current, i.e. the battery driving the generator)

3. It splits two ways. Each direction is separately fused. One goes to the generator armature, the other to the regulator "A+" terminal.

4. The armature side (larger fuse) goes through the aux gen armature, and then to ground.

5. The regulator side (smaller fuse) goes to the regulator "A+" terminal.

6. The regulator's "F+" terminal goes through the generator field, then to ground.

7. The regulator's "A-" terminal goes to ground.

All the wiring is good, I inspected, disassembled and beeped everything out myself. Supposedly, this setup worked in the past. It is not working now. On engine 2, everything is stone dead, 0 volts on F+ and A+.

On engine 1, there is about 30 volts on F+ and A+, and that increases very slightly with engine RPM, but nowhere near the required 74V. Turning the voltage knob on the regulator has no effect at all (these are EMD "black box" types, one is 8330790, the other 8351980.)

Here's what I don't get. This entire apparatus is below a diode. Power can only leave the generator/regulator area, the regulator has no access to battery power, only to power it itself generates. How does the regulator get any power to initially excite the generator? Why does one side work a little and the other not at all?

The generator is initially excited by residual magnetism in the field.
If the field has lost all of it's residual magnetism, an arcane procedure known as "flashing the field" must be perfomed, accompanied by strange chantings of words like Volt, Ohm, Ampere, Henry, and Gauss, as well as the marvelous smell of ozone.

http://www.dieselduck.ca/machine/03%20e ... erator.htm

Jeff

It would not surprise me if this residual magnetism explains the difference why one gives some voltage and the other none at all. And indeed this would explain... I think the last regulator upgrade relied on residual magnetism. Over months, this magnetism wore off and the regulator was no longer able to bootstrap itself using residual magnetism. This aux gen is designed to have some excitation current from the battery, that is clear from the original schematics.

I am concerned that our diode may be too perfect. Instead of a diode, the original GE design employed a reverse current relay operating a contactor. This relay needed to flow some current simply to sense the direction of current. So it allowed some reverse current, with a reverse resistance of about 450 ohms. That is enough to flow roughly 0.1 amp through the regulator and field. Since the regulator fuse was only 4A, that is something. Would that be enough to assure initial excitation? Given that the regulator is driving essentially no load until it reaches battery voltage and is able to push past the RC relay or diode.

Exciting the field. I remember it well. I was trying to revive a reluctant 50-ton GE but was unable to get the auxiliary generator to do its thing. I got a locomotive electrician to come by, and he quickly confirmed my diagnosis. With nothing more than a straightened-out wire coat hanger, he excited it again. He placed one end of the wire on a nearby metal strut, said some magic words, and touched the other end to a precise location on the spinning generator armature. Presto, zappo! We had power!

74 volts in a 44 ton GE, are you sure about that as my experience with small GEs has been they have 32-36 volt electrical systems?

Mike Tillger

Yup, 74v same as an Alco or EMD. Battery voltage fresh off the charger is 68v.

My understanding is that there were different philosophies with the smaller GE units. The 44 ton and 70 ton units with the slower turning engines and four traction motors were considered 'railroad' locomotives, and used the higher control voltage. The 25 and 45 ton units, with the higher speed Cummins engines (typically) and only one or two TMs were considered industrial, and used the 36 volt system.

One of my bosses, ages ago, had been a field service rep for ABB, and once told me the story about when he jump-started a large tanker or container ship. The ship had been laid up for some time, and the ships service generator wouldn't produce any voltage. So he wound up taking the battery our of his rental car and flashing the alternator field-

On some older autos with electromechanical voltage regulators containing a separate field relay, the relay picks up to supply field current only when the alternator starts generating. To avoid a "Catch 22" situation, besides residual magnetism, they supply a small initial field current by way of the ALT warning light (and parallel resistor). Why they don't just operate the field relay's coil off the ignition switch I'm not sure but perhaps because this way the field doesn't run down the battery if the ignition switch is on for some reason but the engine isn't turning or the alternator isn't producing for some other reason.

Maybe some similar way to get field power to the generators to start them is what's needed here.

Steve

Your current setup is probably part of the issue, as the gens can't get any flashing voltage from the battery. Many car generator/alternators won't make any voltage until the engine is revved up. So before you try anything else bring the engines up to max RPM and down again and see if they both don't pick up. The automotive ones that have this issue usually only need a blip on the throttle when new but sometimes they get old and weak and you really got to wind them up to get charging to start.

next you can try to jump the diode out and see if that helps (give the engines a rev again here). Really since you have a battery switch that should be pulled when the loco is idle, you can do away with the diode totally...

fully charged voltage on a 64 volt 'nominal' system should be about 67.5v much less then that and your batteries are undercharged. freshly charged they will show higher voltage, but they should settle down overnight (Called dissipating the surface charge) to closer to 67.5. try not to let the charging voltage ever exceed 78 for any length of time, 72 should be about perfect for normal running.

Robert

Interesting. We will have an opportunity to wind out the engines tomorrow. But I don't want that to be a regular thing. Gotta be gentle with these old machines... we can't afford to thrash one part of the machine to compensate for a problem with another.


That's exactly what I tried. I bridged across the diodes at the top of the circuit. With light bulbs, in fact, since there's nowhere else you're going to find a 360 ohm 40W resistor round here.

The bulbs lit kind of medium, the way 120V bulbs light on 64V. After engine #1 started, it was still about as bright. (I had engine #2 to compare it with.) Revving the engine had no effect. After a few minutes, it started getting somewhat dimmer. (dimmer is good, it means it is getting closer to battery voltage). Did not have a voltmeter with me for that attempt. The bulb never went out, so it never got near diode voltage.

I shut down #1 and started #2. That one got dimmer and dimmer then a "CLICK" and it got bright again, repeating every 2-3 seconds. Revving up about 50% seemed to speed up this a bit, as did turning the voltage adjust. This was different and better than what I was getting before, but still nowhere near the 69V needed to overpower the diode and start to charge the battery.

I went back and re-measured armature and field resistance with a simple Fluke meter, and found the fields were the same, so that's good... #1's armature was 10 ohms... and #2's was 0.9 ohms with 200k resistance to the frame of the generator. I can't find where GE documents the correct resistance, so I don't know which one is right, but I'm guessing not #2... :(

Don't waste one more minute on #2, it's blown. Any GOOD generator shop should be able to fix it. I'm betting the regulator is blown too, as .9 ohm at 65 volts is waaay too much current.

To my way of thinking, 10 oms is still too low. But if you get #2 rewound you'll have a number to compare it to and that will help.

Robert

Regarding what I describe above with the lights... here's a video of that.
http://www.youtube.com/watch?v=IVa12qaLEYc