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Old 11-05-2012, 05:40 PM   #1
tundra61 OP
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Flashing a generator

All,

I lost power at my house due to Sandy and have been running a portable Honda generator. It stopped producing electric so I flashed it using the reverse drill trick. I understand what the drill does but am not sure I understand what happens to a generator requiring that it be flashed to begin with. Can somebody explain what causes this? Also, is this the sign of a bigger problem?

Thx,
tundra61
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Old 11-05-2012, 05:47 PM   #2
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Help a dummy like me understand what "flashing" a generator means... I'm guessing now...
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Old 11-05-2012, 05:52 PM   #3
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It has to do with the magnetism (or lack of) in the coils. Better explained by somebody else: http://en.wikipedia.org/wiki/Excitation_(magnetic)
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Old 11-05-2012, 06:02 PM   #4
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Well, that certainly clears it up...





I'd say if your honda isn't making electricity, it's broken... Unless it's just out of gas...
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Old 11-05-2012, 06:06 PM   #5
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I did the drill trick which is to plug it in to the generator and turn the chuck in reverse creating a current back into the generator and all is fine - but I am trying to understand what causes the initial problem.
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Old 11-05-2012, 06:09 PM   #6
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http://www.dieselduck.net/machine/03..._generator.htm

Possible you have an intermittent open circuit in the field coil?
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Old 11-05-2012, 06:12 PM   #7
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Quote:
Originally Posted by tundra61 View Post
It has to do with the magnetism (or lack of) in the coils. Better explained by somebody else: http://en.wikipedia.org/wiki/Excitation_(magnetic)
Your article is a dead end link.
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Old 11-05-2012, 06:46 PM   #8
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Quote:
Originally Posted by tundra61 View Post
I did the drill trick which is to plug it in to the generator and turn the chuck in reverse creating a current back into the generator and all is fine - but I am trying to understand what causes the initial problem.
Not an electrical engineer by a long shot but I have a few generators. I think most of the time a loss of residual magnetism is due to a generator being stored over a period of time without use. I've never heard of it happening while a generator is running.

Not much help.

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Old 11-05-2012, 09:48 PM   #9
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Your article is a dead end link.
it's easy to fix the link.
http://en.wikipedia.org/wiki/Excitation_%28magnetic%29
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Old 11-05-2012, 11:01 PM   #10
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If you let them sit without use, they lose the residual magnetism they need to self-excite the field. Nothing serious, just a little annoying. Running them every (or every other) month for a little while (maybe 15-20 minutes?) with a heavy load should be enough to keep the magnetism strong and ready for use. This is just info I picked up while reading about generators after I bought an used older model with low hours, luckily the previous owner started it up regularly although not regularly enough to burn up the gasoline before it turned a nasty yellow color. Surprisingly it runs like a top, first pull start every time. Got some Seafoam in there now to clean it out and stabilize the fuel.
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Old 11-05-2012, 11:04 PM   #11
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I know this one....

the old iron core generators had what was called the "residual field"... it is a permanent magnetic field stored in the iron cores (poles) of the field circuit. (the field circuit is copper wire wound around an iron or steel block). the initial excitation comes from this residual field... as the armature turns, the residual induces a small voltage which is fed into the field windings. an increase in field strength (the electromagnetic field plus the residual) causes the voltage to rise to system value at which point the regulator takes over to modulate the electro field.

loss of residual can be because of long periods of no use, a sharp blow, or from reverse polarity being put on the field coils.

to restore the residual, current is passed through the field windings in the same direction it would normally go. this will re-magnetize the pole pieces (core) of the field. it is usually done with battery power & is also known as flashing the field. sometimes you will hear somebody mention "flashing the regulator"...this is a misnomer. it came into being because the terminals on the old style regulators provided a convenient place to make the connections required to flash the field. it is really the field that need the current, not the regulator itself

P.S. the coils themselves are copper wire... no can magnetize copper right? the permanent field resides in the iron

residual voltage on it's own is typically 5-15% of system value... thats an old trouble shooting rule of thumb. run the gen, if you get 2 volts on a 12 v system thats the residual by itself. it means the regulator circuit or the field coils are open.

zero voltage means a loss of residual, a shorted armature, or a broken brush

Beezer screwed with this post 11-05-2012 at 11:19 PM
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Old 11-05-2012, 11:29 PM   #12
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as for turning the generator backwards.. not sure why that worked. most modern small generators use a permanent magnet for that initial excitation. it's more like a real magnet than just lumps of iron (like alnico). power is generated in a stationary stator winging, with rectification by diodes. since the stator is AC anyway....I see no reason why turning the rotor backwards would make any difference. It shouldn't. a true loss of residual would not give you the initial excitation. restoring lost residual would require flashing, and that needs an external power source.

all I can think of is the brushes to the rotor (which supply's the electro field) or the slip rings may have had some crud on them which was knocked off or polished off a bit by changing the rotation.
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Old 11-06-2012, 02:01 AM   #13
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Quote:
Originally Posted by Beezer View Post
all I can think of is the brushes to the rotor (which supply's the electro field) or the slip rings may have had some crud on them which was knocked off or polished off a bit by changing the rotation.
this is what I think is going on.

Perhaps the OP can explain the "drill trick" ?

I understood "flashing" to be applying power to the exciter circuit from another source.
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Old 11-06-2012, 04:01 AM   #14
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Both methods, (drill too..) are explained in understandable form here:
http://www.endtimesreport.com/dead_gen.html

Just note that 6 or 12 volt generators on older cars/motorcycles
are flashed with the 6 or 12 volts, not the "110" in the article....

CycleDoc59 screwed with this post 11-06-2012 at 04:05 AM Reason: mis-type
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Old 11-06-2012, 07:27 AM   #15
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Quote:
Originally Posted by CycleDoc59 View Post
Both methods, (drill too..) are explained in understandable form here:
http://www.endtimesreport.com/dead_gen.html

Just note that 6 or 12 volt generators on older cars/motorcycles
are flashed with the 6 or 12 volts, not the "110" in the article....
FWIW I remember the old time vehicle generators also needed to be flashed with the correct polarity if you were converting from positive to negative ground
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