Harbor Freight has an 800w inverter on sale for $45. It claims to have
surge capacity of 1800w.
My refrigerator draws 13 amps for a second when starting, and then less than
So, will the inverter be able to start my refrigerator?
Is it safe to run a refrigerator on modified sine wave? When they installed
my furnace last year they told me the msw inverters will fry the furnace,
but refrigerators seem less demanding.
I don't plan on using it, but for $45, back up to my generator would be
nice; but not if it will trash a $1,000 refrigerator.
And since I am on the subject, what would happen if I tried to start it with
inadequate current? Would it burn out, or is there a safety feature? I
tried to get an answer from the manufacturer, but they wouldn't tell me.
Modified sine wave means what? Nothing useful because it is
not nor describes a number. One critical number is THD. Does
that inverter even provide a THD number?
Many computer UPSes output modified sine waves. That means
they are 'computer grade'. Another term used to confuse.
'Computer grade' may mean it is only good for computers
because inverter may damage small electric motors. Myths
forget to mention that computers can be more robust than other
appliances. A modified sine wave is not destructive to a
computer but could be destructive to something less robust
such as a furnace.
But again, what is the THD number? It's not which is more
demanding. It's about which is more robust. But then I have
told you little that is useful since I provided a subjective
word (robust) and did not provide numbers.
It means they use a stepped waveform to simulate a sine wave(instead of a
pure square wave),so it's still full of harmonics,but at lower amplitudes.
So there is less energy at the higher freqs to be dissipated as heat.
But still more than a pure sine wave.
Computer power supplies these days are all switchers,so the input AC is
immeidately rectified and filtered to DC,so the harmonics would not bother
them.They have EMI filters on the inputs anyways,to keep internally
generated harmonics and noise from going out the input lines!
It seems that furnace controls operate on 24VAC from a 60Hz transformer and
the motor runs on 220VAC/60Hz.(I believe).Thats a lot of current for an
inverter to supply,though.
No. Don't count on any "surge capacity".
Some modern fridges have electronic controls.MSW inverter might harm those.
electric motors do not like undervoltage for any long time period.
"brownouts" burn out motors.
Your inverter output V would drop then either recover,or decide it can't
maintain and shut down all the way.Depends on how sophisticated the
circuitry is;for a inexpensive one,it probably will not have the better
I've got a couple inverters which do mod sine. First, a common volt meter
reads 90 volts, not 115. If your meter reads 90, it's just account of the
The book I had with mine said that charging things like flash lights or
shavers (which don't use a transformer) will fry the charger. But, the
implication is that charge systems with a transformer are OK.
I don't know the answer about furnace boards. (I'd like to know cause I do
have a mod sine inverter, and also a furnace with a board).
Does your refrig have a circuit board, or is it all analog?
Pay attention to whatever Stormin Mormin says, he knows lots and lots
about tricity. Especially pacacitators and circuit breakers.
It would be better to ask this on alt.energy.homepower.
I know that Trace, Xanax and Outback inverters are used
to run refrigerators. I also know that there have been
reports that MSW inverters won't start up furnace motors.
Bottom line: There is a good chance it will work. But,
get better advice on alt.energy.homepower.
Just my $0.02 worth. Hope it helps
2% THD would be sufficient for anything. A higher number on
the inverter should be less than what specs permit for that
appliance (ie furnace). 20% THD is probably what that
inverter is outputting meaning that it causes stress to
refrigerator and furnace - but is more than sufficient for
Notice a shortage of numbers. This because too many just
somehow know and don't need the numbers. Well, to answer your
question, numbers are required. There is no way to answer
your question without those numbers. Less than 1% of us
understand those numbers ... which is why the other 99% should
be demanding numbers. So that the 1% cannot blow the whistle,
many manufacturers intentionally don't provide numbers. Then
people in your position only get answers from those who don't
really know such as, "I did it and it did not explode.
Therefore you can also so it."
I run 2 fridges on a square wave inverter (1700W) and they perform
perfectly. No odd noises. I just have to start them one at a time. One
fridge is about 6 years old and the other is less than 6 months.
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