A month or two go I asked here if a Yamaha EF1000, which will produce 8a,
will start my refrigerator that draws 13a at startup.
The majority opinion was probably; the fridge probably doesn't need 13a to
start and the genny will probably produce more than 8a for a short time; so
between the two...
As it happens, one retailer claimed that Yamaha told them the EF1000 will
produce 3500w for 3 seconds, which is not supported on the Yamaha website.
I called Yamaha and was told that their website says it will produce 1000w,
so that is all it will produce. Eventually I got to the supervisor's
supervisor, who said that it will do 3500w, but they are not making that
claim anymore. (presumably they got complaints from people who didn't
understand what "3 seconds" meant.)
So I bought the EF1000. It will actually start my shopvac, which draws 16a
at startup. I haven't pushed it any harder, so I can't actually verify the
3500w, but it is good enough.
Alls well that ends well.
Incidentally, Honda told me the absolute max on their EU1000 is 1000w and it
will not start my fridge; I don't know if someone higher up would say
There is no such thing as "peak-to-peak" ratings for a generator measured in
You might be thinking of "peak", "surge", "maximum inrush" or other such
terms which describe the brief maximum current which the generator (and its'
associated fuse/breaker) can deliver.
"Peak-to-peak" is used in electrical engineering to describe the amplitude /
height of an analog waveform when measuring from the maximum negative to
positive swing. For a sine wave (the most common form of alternating
current), it represents a value which is about 2.8 times the average / RMS
Does this generator use a DC generator with an inverter?
I think that in the case of a generator with an inverter, the surge
rating is limted by the electronics in the inverter.
With the old fashioned mecahnical AC generators, the surge rating is
much higher and is limited by the resistance of the windings...
Well, Yamaha says it will produce 3500w for 3 seconds. In the manual they
say it will simply shut off in event of an overload, and they don't warn
about overload breaking it. So, it seems likely that 2000w for 2 seconds,
without the genny shutting down, won't damage it
Most likely neither the windings nor the inverter electronics will actually
be the limiting factor. All generators use some form of circuit breakers
and/or fuses to limit both the continuous current delivered as well as the
transient surge demand which is imposed by big inductive loads like motors,
etc. The breaker / fuse is deliberately chosen to protect the inverter /
windings / etc.
Unless somebody is deliberately trying to circumvent this design by either
putting a jumper across the breaker/fuse or repeatedly overloading the
circuit and flipping the breaker on manually, the generator should know how
to protect itself against the common start-up demands which typical
It is entirely possible though that the generator is designed and fused to
only deliver a very small amount of extra transient surge current above its'
normal steady state continuous rating. In this case, the 'fridge' could blow
the breaker every time it cycles on its' compressor, if the generator is
You just explained what I said in plain language.
Yup, peak to peak, average, rms three terms commonly used.
Remember stereo salesman used to use peak music power to sell El Cheapo
amps? Kikewise! Marketing gimmicks are many and confusing to gemeral
Peak to peak means one thing and "peak" means another. "Peak" music power as
mis-used by stereo salesmen (until the FTC forced the industry to adopt
correct and standardized terms) was a term used to exaggerate the true
average/RMS power which an amplifier could deliver. This has absolutely
nothing whatsoever to do with "peak to peak", the term you originally
Peak-to-peak, as the reference in Wikipedia correct states, merely indicates
the size of a waveform from its lowest (negative) peak to its highest
(positive) peak. If you have a scope in front of you, looking at a waveform,
the peak to peak voltage is nothing more than the height of the signal in
Generators make electricity, and one could describe the waveform they
produce by saying it has a peak to peak voltage of 336 volts (assuming a
sine wave and 120 volt RMS generator) but this is not a description of the
surge capacity of the generator.
When specifying / characterizing the ability of a generator to provide
transient, brief additional power, the term which electricians and
electrical engineers use is "peak" or "surge" or "transient", but never
"peak to peak". It may seem or sound similar, but is not the same thing.
The shop vac has a universal motor, one with brushes and a wound armature,
like in a power saw. The refrigerator uses a different type motor, it may
not start even if the shop vac does. Why not just try it?
As others have said, you have not in any way verified that your generator
will start your refrigerator. You have only verified that it will start your
shop-vac. These are the kinds of tests that marketers like to demonstrate,
to make people think they have proven something they haven't. If it is
important that the generator start the refrigerator, try it several times. I
suspect the 13A refrigerator will be harder for the generator to start than
the 16A shop-vac but since there are several unknown variables it cannot be
determined except by testing. I believe it will be okay.
What matters is how the different appliances react to low voltage.
The shop vac has a universal motor, which will draw less current on
lower voltage and run slower. It's driving a fan, which is almost zero
load at startup from zero speed. So if the generator's voltage droops
under load, the shop vac will just take a while longer to get up to
The refrigerator uses an induction motor, which draws more current when
voltage drops. It's probably driving a piston pump, which should be
easy to start if the fridge has been off for a while and pressures have
equalized, but not as easy as a fan. So you may find that drooping
voltage under overload means the refrigerator won't start at all, and
either the motor or the generator will eventually trip on overload.
Since people were actually interested, I tried it; leaving 5 minutes between
(Yamaha claims 3500w for 3 seconds, and then 1000w for 20 minutes, finally
Wattages are per the meter on the transfer switch, so they are approximate.
When I tested on commercial power the refrigerator drew 13a for about a
second, and then 1a to run.
The first time it went to 1500w for about 5 seconds and the generator
tripped out. I reset the generator.
The second time it went to 1500w for a second and then dropped to 100w.
The third time it went to 1500w for 3 seconds and I flipped the transfer
switch off, since it seemed to be like the first time and I didn't want to
go upstairs to reset the generator.
The fourth time was like the second; all normal.
I have have tried it maybe 3 times on commerical power and it has never held
at 13a like 1 & 3.
So the question is:
Does the generator somehow cause it to sometimes take longer to start up, or
is that a refrigerator issue that I just never happened to see before. I
don't know enough about refrigerators to know.
But, as I understand it, inverter generators hold the 120v; when they can't
do it, they trip out. So, they only give 120v or 0v, never low voltage.
I hope never to use this on the refrigerator; I have a Honda EU2000 that I
have used in 3 power outages. I bought this for another purpose where the
EU2000 was too heavy, but liked the idea of having it as a backup for the
Hey, I hope never to use the EU2000 either; in the 2 years since I put a
transfer switch in we haven't had an outage.
The induction motor in the refrigerator will take longer to start if the
voltage is low.
That's probably true over a long time, but not necessarily true for
short periods. If you overload the generator, the voltage almost
certainly *will* drop somewhat. This may cause the generator to trip in
a short period (and it did on a couple of your tests), but if the
refrigerator comes up near operating speed before that the overload
will be gone, the voltage will recover, and the generator will decide
not to trip after all.
To be sure of what's going on, monitor the generator output waveform
with an oscilloscope. Then you'll know. A meter may not respond fast
enough to tell you anything about a transient voltage drop.
The shopvac has a universal motor and the fridge has a capacitor-start
induction motor. They are not equivalent loads. Your test is invalid;
sorry. (and I'm not sure which is the harder one to start)
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