Forum Discussion

JnJnKatiebug's avatar
JnJnKatiebug
Explorer
Jun 29, 2016

Pure Sine Wave vs Modified Sine Wave for fridge

I am thinking about changing my fridge out to a residential unit but I would need to be able to run it from my inverter for up to 8 hours at a time. (I have 4 new Trojan T105 batteries) I have read where the residential refrigerators do not work on Modified Sine Wave. In my manual it says my inverter (Xantrex Freedom 458) is a Filtered Modified Sine Wave. What is the difference between Modified Sine Wave and Filtered Modified Sine Wave? Does anyone have any experience running the residential fridge on this inverter? I do not want to change out the inverter to a Pure Sine Wave.
  • wa8yxm wrote:
    Modified sine wave: Long list of things that do not play nice with it. Can generate major Radio Frequency interference affecting nearby Radios, Televisions, Sat Receivers and audio ampolifers

    Filtered modified sine wave: Same list of things that do not play nice.. Filtering greatly reduces the radio frequency interference in some cases to the point where it drops below the "noise floor" and is thus undetectable (good thing).

    True Sine Wave.. Very very short list of things that do not play nice (Entier list: Anything needing more power than it can produce) Very little if any Radio Frequency Interference.. Very clean power. often better than commercial power.

    Batteries: 2 pair of Trojan T-105 or equal is minimum for a 2KW inverter

    You have 220 Amp Hours times about 10 for Watt hours there, or 2,200 watt hours

    Fridge is about 100-300 watts depending on model. that's 10 hours max if your wiring is perfect and you are lucky.

    This is reduced by other loads (Explosive gas detector for example) and increased by Fridge's "Down time" (when nothing is running)

    Page 3: Many have run Compressor type (residential) fridges on MSW and no problem... However the manufacturers say "Do not"... Me.. I prefer the absorption fridge cause I can run it on very little 12 VDC plus a tank of Propane if I have to.. and sometimes.. i ahve to.


    Has anyone looked at the filtered MSW inverter output waveform on an oscilloscope? Depending on the cutoff frequency and the number of poles of the low pass (or bandpass)filter it could be a pretty decent waveform meaning the 2nd and higher order harmonics are attenuated significantly. If however the filtering is only removing much higher (past the 5th harmonic) frequency components such as switching noise then it will probably not act much different than other MSW inverters.
  • I bought a plug in volt meter this weekend and plugged into one of the outlets that is powered by the inverter. It only shows 95 volts. Looks like I have a problem with my inverter anyway. Show power ranged from 115 to 120.
  • JnJnKatiebug wrote:
    I bought a plug in volt meter this weekend and plugged into one of the outlets that is powered by the inverter. It only shows 95 volts. Looks like I have a problem with my inverter anyway. Show power ranged from 115 to 120.


    Of course ... any meter designed to read a pure sine wave signal will incorrectly display voltage from a modified sine wave inverer which you indicated in your original post is what you have. :R
  • Try reading the voltage with something plugged in and using power
    Your TV a small fan ?

    Often the no load idle voltage will read low
  • JnJnKatiebug wrote:
    I bought a plug in volt meter this weekend and plugged into one of the outlets that is powered by the inverter. It only shows 95 volts. Looks like I have a problem with my inverter anyway. Show power ranged from 115 to 120.
    Need a True RMS meter to read MSW.
    And as I said earlier motors and microwaves are looking for this peak voltage that does not exist with MSW.
    Yes check it again with an appliance running.