Repair Generator by Field Flashing

[ibdilbert01]

Sent: 9/30/2007

I did a quick search our archives and didn't find anything that told how to do this. I aquired a generator a few days ago that the PO had installed a new engine on but couldn't get it to make electricity. He sold the unit to me at a good price and I was going to put a new generator head on it. After doing some reading, I found the following....

Field Flashing of Portable Generators

This tip comes from the Briggs & Stratton Customer Education Department. As an alternative to flashing a rotor winding with a battery applied to the brushes, an electric drill may be used. Follow these steps to flash the generator:

* Plug the electric drill into the generator receptacle. (Cordless drills do not work)
* If the drill is reversible, move the direction switch to the forward position.
* Start the generator
* While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.

Use caution not to get your hand or other materials caught in the chuck. As soon as the field is excited, the generator will produce power and the drill will turn on.

The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor windings, which is fed back through the trigger, cord and into the generators receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field, which is intensified due to the iron core of the stator laminations. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.

If flashing the field does not make the generator work, you may have additional problems, besides a lack of magnetism in the rotor. Further testing will be needed. Hopefully, this will give a simple way to field flash your generator if needed - Bruce Perrault http://www.perr.com/tip16.html

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This actually worked. I was surprised, but the generator now runs just fine. So if anybody has a generator that isn't making electricity, maybe try this first before taking drastic measures.

[Slantsixness]

Sent: 10/1/2007

Caution:

You cannot use electronically controlled drills for this. (usually these drills are marked "electronically controlled")
Many newer corded drills are actually DC motors and have electronic controls and will produce no current if spun either direction (there's a rectifier that prevents this from happening, which is what you need to do.)

In most generators, this same thing can be done with a household portable fan, just remove the fan sheild, turn it on High (Low and medium shunt the input with a resistor and reduce the effect), and spin it backwards. (and step back when it catches.) any inductive product will induce current in the generator fields....

The reason I say "Fan" is that most of us have one of those already in the motorhome, and yes, you can just plug it in inside the motorhome.. you don't have to be out by the generator.

This only applies to older generators that do not have waveform regulation, and it only happens when the motorhome or genny has been sitting unused for a really long time, or the armature has been replaced.

Tom

[denisondc]

Sent: 10/1/2007

We used to have to do that 'flashing' to generators in older automobiles, in case the iron core in the stator lost its magnetism [from being dropped on a concrete floor for instance]. We called it 'polarizing', and it was possible to get the field polarized (magnetized) backwards. The generators that didnt have electromagnetic regulators (like my 32 Chevy & lots of pre-war farm equipment) would then produce negative 6 volts if you spun them.
The fix was to drop them on the concrete floor again, then polarize them correctly

[Madathlon]

Woo your horses there, Field flashing a newer electronic Gen can cause total failer of its control boards. ONLY flied Flash older CCK/OCCK or any pre 78 Gen.
Also any good Gen Shop ( Like Goss Electric in Shasta Lake City Ca 530-275-1861) can and will be happy to help you flash your Gen fields. If you ever pass though Shasta Lake City Ca, Look them up. There the only Shop in 100 miles that still works on the Older Gen and carries many of the parts on hand.

[ibdilbert01]

I must be pretty darn lucky, as I've been a generator flashn' fool since I learned the above trick.   All models and years too!     I usually try to find an angle grinder with a stone on it and drag it across the ground.   W%  And so far, I've had 100% success rate.   

[Gary Eddy]

You guys are WAY ahead of me. I am an experienced mechanic and never had more trouble than working on my 6.7kw Onan generator. After constant frustration and multiple VERY expensive parts that didn't solve the problem, I took it to Cummins/Onan.  They are expensive but fixed it right on two separate problems.

I VOW AND SOLOMLY PROMISE TO ONLY DO OIL AND FILTER CHANGES HENCE FORTH AND FOREVER MORE ON MY GENERATOR. 

[Neil Carrick]

I had a very similar experience with the genset on our Chieftain..  the drill was hard to turn by hand so put a cordless onto the end of a tool bit to drive it and it took off in just a few winds. I was told of this procedure by a local small engine guy who said he watched a utube video.. 
All kinds on information out there, just got to know how to ask for it.

Neil and Shelley