A refrigerator on a modified sine wave inverter?

Discussion in 'Home Repair' started by Toller, Aug 26, 2005.

  1. Toller

    Toller Guest

    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
    2 amps.
    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.
    Toller, Aug 26, 2005
    #1
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  2. 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
    waveform.

    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?

    --

    Christopher A. Young
    Do good work.
    It's longer in the short run
    but shorter in the long run.
    ..
    ..


    "Toller" <> wrote in message
    news:JSLPe.5398$...
    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
    2 amps.
    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.
    Stormin Mormon, Aug 26, 2005
    #2
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  3. Toller

    w_tom Guest

    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.

    Toller wrote:
    > 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 2 amps. 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.
    w_tom, Aug 27, 2005
    #3
  4. Toller

    Matt Guest

    Matt, Aug 27, 2005
    #4
  5. 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.

    "Toller" <> wrote in
    news:JSLPe.5398$:

    > 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 2 amps.
    > 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.
    >
    >




    --
    Just my $0.02 worth. Hope it helps
    Gordon Reeder
    greeder
    at: myself.com

    Hey EVERYBODY!
    Unity means let's try to meet each other halfway
    Gordon Reeder, Aug 27, 2005
    #5
  6. Toller

    Jim Yanik Guest

    w_tom <> wrote in news::

    > Modified sine wave means what?


    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.

    > Nothing useful because it is
    > not nor describes a number. One critical number is THD. Does
    > that inverter even provide a THD number?


    Doubtful.

    >
    > 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.


    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.

    >
    > 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.
    >
    > Toller wrote:
    >> 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 2 amps. So, will the
    >> inverter be able to start my refrigerator?


    No. Don't count on any "surge capacity".

    > 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.


    Some modern fridges have electronic controls.MSW inverter might harm those.

    >>
    >> 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.

    >


    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
    circuitry.

    --
    Jim Yanik
    jyanik
    at
    kua.net
    Jim Yanik, Aug 27, 2005
    #6
  7. Toller

    Toller Guest

    "Gordon Reeder" <> wrote in message
    news:Xns96BECF4DCA45Agreederworldsharenet@216.168.3.44...
    > 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.
    >

    Thank you; I will try there.
    I presume it is like everything else at HF; cheap as possible, but just
    barely doing the job.
    Toller, Aug 27, 2005
    #7
  8. Toller

    w_tom Guest

    Without that THD number, then no one can responsibly answer
    your question here or there.

    Toller wrote:
    > Thank you; I will try there.
    > I presume it is like everything else at HF; cheap as possible, but
    > just barely doing the job.
    w_tom, Aug 27, 2005
    #8
  9. Toller

    Toller Guest

    I am guessing that THD means total harmonic distortion, so something like
    that, and also that HF doesn't provide it.

    But, in case they do, what sort of THD would I be looking for?

    "w_tom" <> wrote in message
    news:...
    > Without that THD number, then no one can responsibly answer
    > your question here or there.
    >
    > Toller wrote:
    > > Thank you; I will try there.
    > > I presume it is like everything else at HF; cheap as possible, but
    > > just barely doing the job.
    Toller, Aug 27, 2005
    #9
  10. Toller

    w_tom Guest

    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
    electronics.

    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."

    Toller wrote:
    > I am guessing that THD means total harmonic distortion, so
    > something like that, and also that HF doesn't provide it.
    >
    > But, in case they do, what sort of THD would I be looking for?
    w_tom, Aug 27, 2005
    #10
  11. Toller

    Mark Guest

    On Fri, 26 Aug 2005 21:31:21 GMT, "Toller" <> wrote:

    >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
    >2 amps.
    >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.


    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.
    Mark, Aug 30, 2005
    #11
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