Generator clamp up

On-engine electrical issues discussed here.

Generator clamp up

Postby f4dj79 on Tue Feb 10, 2009 8:29 pm

While doing some trouble shooting the engien crew on the North American Eagle pulled to only generator we are using to see if it had seperation of the coupler. I am glad we did pull the unit, sure enough the heavy generator fall out when we loosened the holding clamp. After close inspection it was determined that it sheared off do to a heavy loading. We had done many days of searching for the cause of the no internal power problem. When the generator does not porduce power output it means the coupler is sheared off. The exact reason for the sheared coupler has not been determined however, we probably had a direct shorting or a runaway power cycling. At the time was did not know this but our voltage regulator was not working and that may very well be what cuased the malfunction. Moral to the story, try not use fifty year old electrical parts. We have since located several VR's and installed one, we will be taking the beast out for some engine ground runs to see if this does the trick. Did I mension that we also added some new wiring, the fifty year old exposed wiring had even failed internally which caused high resistance. Nothing that we did not already know about however when you are no small tight budget some things get over looked. It is funny how this project has matured to the point that we are now fixing everything that we missed ealry on. My best guess we were more worried about the engine and suspension early on and now we the time to devote to the electrical bugs. The electrical system will be ready for our spring test runs.
WB
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Re: Generator clamp up

Postby j79guy on Fri Feb 13, 2009 7:32 pm

Shock loading will shear the shaft. By this, I mean shock electrical loads. Loads on the generator have to be introduced "soft", or from light off, to gently ramp the load or the shaft will shear. By simply closing a breaker when the engine is at speed, this will cause a high current inrush spike, and pop, there goes the shaft. At speed, think of electrical loads the same way as hydraulic loads on a pump, with no accumulator.

Robin.
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Re: Generator clamp up

Postby f4dj79 on Tue Feb 17, 2009 5:53 pm

I agree Robin in our case the F-104 had all the original wiring hacked out during de-mil. and some of the wires that were left are in bad shape. Some of the black boxes that control power are long gone. We have had to make do with what we had. We added some new circuit breakers, located used voltage regulators and replaced some of the wiring. Then we got to look closer at the wiring schematic, and located the field leads from the VR to Generator. We found A-,A+ and B+ wires that make the system operate. Ed, dug around in the wires and also found two missing grounds one at the VR and one at generator. The way we will wire up the VR and Generator will be the same way the oem schamtic wired it. The only exception will be a switched A- lead that will go up the cockpit dash. That will turn on the VR, this should allow the engine to get up to full speed before switching over to internal power to reduce the power spike. Our system is so old that it uses 28vdc to trip the VR to the energized position. That was our trouble all along, the VR would see the generator spinning up with voltage and try to recurve the voltage and current up to the proper settings without the generator being up to full power. The VR would overheat, over-current and under volt. the system and this would cause the generator to also overwork and as Robin mentioned shear the coupler. We now have the system wired up and sometime in the next few weeks do a operational ground run to test out the generator and power systems.
WB
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