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Question on portable generator not producing power

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Posted by Fred F. on June 19, 2009, 1:39 am
I know that this has been asked (and answered) many times before, but
as it did not effect me at the time, I did not fully absorb it.

Here is the description that was passed on to me:

My Craftsman 5600 watt generator (model 580.675610) uses a 10.0 HP
Briggs and Stratton engine and it runs great. While the unit starts on
the second pull after sitting for several months, it does not produce
an AC. The last time I discovered this issue (October 2008), I
contacted Sears and the technician who came out to service the
generator did something called ‘flashing the field coil’ with a small
battery. Apparently the residual magnetism in the alternator weakens
through lack of use and this simple procedure of flashing the coil is
enough to excite the field and it resumes producing AC.

Even though I didn’t need to run the generator over the past winter, I
thought it was important to drain the old fuel out of the tank and
yesterday when I started the generator (for the first time since
October 2008, it would not produce AC. I called Sears and a technician
called me back to confirm the service call, but he told me I would
have to run this unit more often to ensure the residual magnetism in
the alternator didn’t weaken in order to ensure it produces AC each
time it starts.

I find it odd that I would have to start this particular generator
more often in order to ensure a constant flow of AC – each time it is
started. Is this a design fault with the unit or could there be
something wrong with this particular generator?

So, thanks in advance for assistance. Mainly the question is "Is this
an indication of a fault in the unit, or just the design and is there
a way to prevent this from happening if the generator sits for several

Posted by Martin Riddle on June 19, 2009, 2:03 am

It could be the excitation coils were designed wrong.  I've only flashed
one generator, a 60 to 50hz unit we had at work after we moved it.
Basically you need to magnetize the armature the field sits on. This
small magnetic field is enough to produce voltage for the field windings
when it spins up.

Heres a manual for that gen

What you need to do is DISCONNECT the field winding and briefly connect
a small 12v battery to the Field winding.

If it’s a constant occurance then you should fashion a small connector
for the field winding and have a battery handy.
Only flash the field when the engine is NOT running.


Posted by Harshana on June 19, 2009, 4:06 am
How about placing couple of strong magnets close to field coils while
the gen is running. Magnets can be removed after it comes back to

Posted by Ralph Mowery on June 19, 2009, 6:06 am

I bought  5 kw generator and had it about 2 years before I even started it.
It worked fine.  Ran it for about an hour and let it run out of gas.  Put it
back up for over a year.  It started fine and produced power then with out
any problems.  I did let some gas set up in a couple of times and it would
not start, but that is not your question.  At no time did I ever have any
problems getting power after I got the motor started.  I now start it about
week or two just because of the gas problem.

That being said, the book for it does show how to flash the field if it will
run but not generate any power.  Some iron/steel will hold the magnetic
power beter than others will.  Your generator probably does not have any
real problem , but does loose the magnitism.

Posted by Tim Jackson on June 19, 2009, 2:25 pm
 Fred F. wrote:

It's not a fault as such, but a combination of design, materials and
conditions of use which allow the residual rotor magnetism to collapse
below the starting threshold.

In cars the ignition light performs this function, feeding a small
current from the battery to a point between the field rectifier and
field regulator whenever the ignition is switched on (and the alternator
is not generating). On a free-standing generator you can't do this
because there is no battery. However it would not be rocket science to
wire a lamp from the field rectifier to a small battery and "ignition
switch" to excite it.

Tim Jackson

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