QST – Devoted Entirely to Amateur Radio www.arrl.org June 2012 49
Technical
by Mark Spencer, WA8SME
A Look at Gasoline Powered
Inverter Generators
Portable power for your ARRL Field Day station
Product Review
Mark J. Wilson, K1RO, k1ro@arrl.org
Bottom Line
Inverter generators have advan-
tages over normal ac generators, but
have some disadvantages as well.
With additional filtering, they can be
made “radio friendly.”
Reviewed by Bob Allison, WB1GCM
ARRL Test Engineer
wb1gcm@arrl.org
The fall of 2011 was a difficult time for
New England residents who experienced the
effects of Tropical Storm Irene and a surpris-
ingly heavy late October snowfall spaced a
month apart. Both storms caused widespread
power outages and those with backup genera-
tors maintained some comforts of normal life.
My generator is an inexpensive 1000 W ac
generator powered by a two stroke 63 cc
engine. It’s enough to start our oil burner for
heat and hot water, plus some lights and the
TV. It’s not enough to run the refrigerator
effectively.
Generators I grew up with all ran at one speed
— 3600 rpm (to produce 60 Hz) — and were
noisy. Today there is a lot of interest in a type
of generator that is technically advanced,
more fuel efficient, lighter weight and quieter
— the inverter generator. Inverter generators
produce high voltage, multiphase ac that is
rectified to dc — similar to an automobile
alternator. This dc power is then converted
back to very clean and consistent ac power by
a solid state power inverter. A microprocessor
controls the process as well as the speed of
the engine. Unlike older constant speed
generators, inverter generators can run at idle,
providing power to small devices. If demand
for more power appears at the generator’s
outlet, engine speed increases. This feature is
intended to improve fuel economy and can be
switched on or off. (The various manufactur-
ers have different names for this feature, but
the concept is the same and I’ll refer to it as
ECONOMY mode throughout the review.)
For this review we chose four widely avail-
able inverter generators in the 2000 W class
— the Champion 73536i, Generac iX2000,
Honda EU2000i and Yamaha EF2000iS.
All of the units were available locally from
power equipment dealers, outdoor stores,
industrial suppliers or box stores in the $600
to $1000 range. Prices shown in the tables
are what we paid but will vary depending on
dealer. Other inverter generator models are
available with lower or higher power ratings.
Generators in this class provide enough
power for a light duty, backup power source
at home or to run a power tool on the job.
But how well do they work in a radio envi-
ronment? All four appear to be attractive
candidates for ARRL Field Day or emer-
gency operation and so we conducted a
variety of tests to determine how “radio
friendly” each of these generators is.
The Tests
Load Test: Each generator was connected to
a load consisting of two strings of incandes-
cent light bulbs adjustable from 0 to 2500 W
in 50 W steps. We measured the generator
output voltage, frequency and sound level as
the load increased up to the maximum rated
output. In each case, the sound level was
measured with a calibrated instrument at a
distance of 9 meters from the muffler side of
the generator. Sound levels will vary depend-
ing on location.
Power per Gallon Test: Each generator was
run out of fuel, refueled with precisely one
cup of gasoline, then restarted and placed on
a 1000 W load until it again ran dry. Running
time was noted and used to calculate kilowatt
hours per gallon of gas (kWh/G).
Waveform Test: The Lab’s Tektronix TDS-
3052B storage oscilloscope captured the
ac waveform during no-load and full-load
conditions. Waveforms for each generator
are available online.
1
No-Load to Full-Load Test: Using the
oscilloscope at a slow sweep speed, measure-
ments were made at the point at which a full
load was applied to the generator from a no
load condition. This tough test shows how
quickly a generator responds to a drastic load
change with
ECONOMY mode on or off.
Oscilloscope plots from this test are available
online (see Note 1).
Conducted Emission Test: Conducted emis-
sion can have a major impact on Field Day or
emergency operation as wideband RF noise
is injected into the power wiring that then
acts as an antenna. For our tests, we used a
100 foot extension cord. Each generator
was swept for conducted emission using a
Rohde & Schwarz LISN (Line Impedance
Stabilization Network) and a Rohde &
Schwarz EFH3 handheld spectrum analyzer.
2
Radiated Emission Test: Each generator was
placed on a cart and rolled around near a
40/20 meter dipole (15 feet high) to check for
radiated emission from the electronics or
ignition system. A nearby battery powered
transceiver attached to the dipole (our simu-
lated Field Day setup) listened for changes in
noise level or ignition noise while I tuned up
and down each band. The transceiver was also
used for listening to conducted emissions with
an extension cord plugged into a generator.
Circular Saw Test: Chances are you will
need a generator to power a tool. I tried to
run a 15 A maximum circular saw with each
generator.
Safety
Before operating a power generator, carefully
read the operator’s manual and safety precau-
tions. All four generator manuals recommend
grounding the generator and determining local
grounding codes. If you have any questions
about wiring or grounding a power generator,
ask a licensed electrician.
I recommend using an in-line ground fault
circuit interrupter (GFCI) outlet with each
generator. They are available online or in
most hardware stores or home centers. If you
plan to use a generator during power outages
at home, have an electrician install a transfer
switch to isolate the generator from the
power lines.
1
Additional ARRL Lab test results are available
online at www.arrl.org/qst-in-depth.
2
See April 2009 QST, page 48 for an explanation
of conducted emission level limits.
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