Pure sine wave Inverters Not all Pure

silvertop
silvertop Solar Expert Posts: 155 ✭✭✭✭✭
in General Solar Power Topics #1
Hi everyone ! I just signed up after following this forum for awhile, and wanted to let you know my results running two digital clocks from two different PSW inverters. The first a SW 2000 Xantrex that I primarily use ,both digital clocks kept same time in 12 hour period. I wanted to run a very small PSW inverter to keep night time tare losses low soo..... i bought a cheap 180 watt PSW Wagan. In the same 12 hours it lost 6 minutes on only ONE digital clock ! I dont have a scope but my guess is IF this falls under the parameters of PSW it just barely does :cool:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Pure sine wave Inverters Not all Pure

    It is also possible that the frequency for the small inverter is not that stable... The 6 minutes out of 12 hours is:
    • 6 min / (12 hours * 60 min per hour) = 0.0082 = 0.8%
    An inexpensive inverter may be 60Hz +/- 1Hz:
    • 1Hz/60Hz = 0.0167 = 1.67%
    So, it is very possible that your Wagan is within its advertized specifications (I did not find the specs. with a quick online search).

    An MSW (or poor quality TSW waveform) inverter would, presumably, have a lot larger timing error.

    -Bill

    PS: Other inverters do have better specifications... the MorningStar 300 watt TSW 12 volt inverter has a 60Hz +/- 0.1 Hz specification...

    But that will still give you:
    • 12 hours * 60 min per hour * 0.1Hz / 60Hz = 1.2 minutes per 12 hour error...
    You might need to find a clock/timer with its own crystal oscillator...

    Short term AC utility power can drift those amounts too... They work for near zero error based on a 24 hour period.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #3
    Re: Pure sine wave Inverters Not all Pure

    I imagine they can vary quite a bit. But here's how the waveform and frequency look on my Prosine 1800W PSW inverter:

    1610.jpg

    1609.jpg

    Compare that to the grid power at my home:

    grid1634.jpg

    The inverter has a better waveform!

    Some DVMs have a frequency funtion if you don't have access to a scope. Just be sure to compare that # against the grid to verify there's no difference in frequency between the two. Sort of a single point calibration.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Pure sine wave Inverters Not all Pure
    silvertop wrote: »
    Hi everyone ! I just signed up after following this forum for awhile, and wanted to let you know my results running two digital clocks from two different PSW inverters. The first a SW 2000 Xantrex that I primarily use ,both digital clocks kept same time in 12 hour period. I wanted to run a very small PSW inverter to keep night time tare losses low soo..... i bought a cheap 180 watt PSW Wagan. In the same 12 hours it lost 6 minutes on only ONE digital clock ! I dont have a scope but my guess is IF this falls under the parameters of PSW it just barely does :cool:


    as was said, the frequency determines a clock accuracy, but i should point out that tare losses are not necessarily lower just because it is a sine wave inverter. you must compare tare loss specs regardless as this can vary widely.

    as to the thread title Pure sine wave Inverters Not all Pure that it is 100% true as what we call a pure sine wave is just a sine wave form that has its total harmonic distortion below 5%. do note that sine wave inverters make the waveform in a similar manner as that of msw, but with more of the waveform transitions taking place within that timeframe. technically all are modified sine wave.
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