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Posted: 8/23/2004 9:25:30 PM EDT
Nope, I'm not talking about exhibitionism at football stadiums here, folks...

My favorite gas-powered generator suddenly stopped producing AC power, even though nothing seemed to be wrong with it.

Got to poking around on the internet, and it appears that this is a common problem. Apparently, many generators rely on a trace of residual magnetism in the steel laminations on the rotor and/or stator, which is used to gradually build up enough current to excite the field winding. If this magnetism ever becomes too weak for one reason or another, the generator never self-excites, and no AC output is produced. Since there's no AC power present to re-magnetize the laminations, the problem remains indefinitely, regardless of how many times you start the generator.

The easiest solution is to "flash the field", which involves briefly applying a DC voltage on the field winding to re-magnetize the laminations. (Interesting side note: There's even a fellow who sells a "field flasher" on ebay for this purpose). Since I didn't want to have to deal with this problem ever again, I added a relay that automatically applies 12 volts to the field whenever the generator's engine starter spins – Thus, the field gets "flashed" every time the generator is started. A few generators come factory-equipped with a similar circuit.

So, here's today's lesson: If your generator stops putting out power for no apparent reason, try flashing the field before you start replacing parts. A free fix beats a $120 fix, every time!
Link Posted: 8/24/2004 3:15:59 AM EDT
Yep............haven't heard that term used since A&P school.
Link Posted: 8/24/2004 3:17:31 AM EDT
Link Posted: 8/24/2004 3:21:25 AM EDT

Originally Posted By QUIB:
Yep............haven't heard that term used since A&P school.

Done it to DC generators. Wasn't aware of AC application though.
Link Posted: 8/24/2004 3:53:44 AM EDT
Link Posted: 8/24/2004 4:10:33 AM EDT
Link Posted: 8/24/2004 4:32:12 AM EDT
I would almost be willing to bet some part of the exciter circuit is bad. The most common part to fail is the "beginning" part of the exciter circuit. It is called a bridge rectifier. Depending on the type of generator, it could be in one package or a group of four diodes. Find the diode(s) and check for proper function. The circuit should be located somewhere near the brushes at the end of the (electric) motor. If any one of the diodes failed, the exciter will not function and your generator will not generate any power. The most common cause of this failure is overloading the generators capacity, usually on startup. It's always a good idea to have the gen running first then apply the load, one item at a time.
Link Posted: 8/24/2004 4:38:56 AM EDT
How Exiciting.


Its a pun , get it . Sorry but someone was gonna say it
Link Posted: 8/24/2004 6:45:43 AM EDT
yep in A&P school flashing the field fixes generators, at work, flashing the field is when you pop your head out of an EE bay on a Air France 777, and the first thing you see is a F/A squats instead of kneels to check safety equipment.


The view was very nice!!!!!!!!!!!!!!!!!
Link Posted: 8/24/2004 7:14:02 AM EDT

Originally Posted By cwd10:
I would almost be willing to bet some part of the exciter circuit is bad.

No exciter circuit in this one. The "excitation" comes purely from residual magnetism in the laminations, which generates a small voltage when the rotor spins, which produces more magnetism, which produces more voltage, etc. Some generators have a small permanent magnet attached to the rotor, exclusively for this purpose.
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