Flashing a generator

Discussion in 'The Garage' started by tundra61, Nov 5, 2012.

  1. tundra61

    tundra61 I wish I had a title

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    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
    #1
  2. concours

    concours WFO for 44 years

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    Help a dummy like me understand what "flashing" a generator means... I'm guessing now...:norton
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  3. tundra61

    tundra61 I wish I had a title

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  4. rapidoxidationman

    rapidoxidationman Easily trainable

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    Well, that certainly clears it up...




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    I'd say if your honda isn't making electricity, it's broken... Unless it's just out of gas...
    #4
  5. tundra61

    tundra61 I wish I had a title

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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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  6. rapidoxidationman

    rapidoxidationman Easily trainable

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  7. Wasser

    Wasser Spilt my beer

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  8. Langanobob

    Langanobob Been here awhile

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    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.

    - Bob
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  9. tedder

    tedder irregular

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  10. buickid

    buickid Lets ride!

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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.
    #10
  11. Beezer

    Beezer Long timer

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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
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  12. Beezer

    Beezer Long timer

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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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  13. RVDan

    RVDan Long timer

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    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.
    #13
  14. CycleDoc59

    CycleDoc59 Wrench Rider

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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....
    #14
  15. victor441

    victor441 Long timer

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    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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  16. papalobster

    papalobster With Gusto!

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    I saw this a bit late to comment. Used to work R&D at Baldor Generators and we would flash a dead gen with a 9 volt battery into the outlet.

    Drill trick works too, essentially you are taking the residual magnetism in the drill rotor and turning it by hand, making it a small generator thereby introducing a small voltage into the generator "remagnetising" the rotor.

    Now, why it lost it's magnetism during operation is a whole different problem:deal

    Is it an inverter generator?
    #16
  17. dtysdalx2

    dtysdalx2 PITA but useful

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    Exciter on a generator...

    Interesting stuff. I've heard of it before. Must be like loosing "magnetism" in a field coil. Magnetism is what makes the electricity...
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  18. Beezer

    Beezer Long timer

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    ah.... turn the drill to make it generate.... that makes sense. drills typically have a series wound (universal) motor. the brushes in the motor would serve as a rectifier. in any case, a voltage at the generator outlet would be fed into the regulator system & re-establish the electromagnetic field which re-establishes the residual (permanent) magnetism. there is no such thing as permanent AC magnetic field right.... so somewhere the exciter current is rectified & can then re-magnetise the cores of the exciter
    #18
  19. WayFar

    WayFar Been here awhile

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    Not sure if it'll work with your particular generator, but if you need to flash the field, and it's electric start, just hit the key again for a split second. Works every time for me, and if you have a starter lockout switch, you get the voltage you need through the system, and no starter grinding. If not...well...whats a little starter overspeed between friends?

    Interestingly, I also used this trick on a forklift that we started by arcing the starter, but once running it produced no power. Couldn't get it onto a trailer. Hit the key again just for shits and grins, and voila!--full power.
    #19
  20. ttpete

    ttpete Rectum Non Bustibus

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    If you have a brushless AC generator (alternator), it has a permanent magnet field similar to those used in most modern motorcycles. It's always energized, and "flashing" is never necessary. Almost all of the small AC generators today are the brushless type.
    #20