Connect with us

A technical question about inverters.

Discussion in 'Electrical Engineering' started by Rob, Jul 18, 2004.

Scroll to continue with content
  1. Rob

    Rob Guest

    Hopefully someone can help.

    I have a pure sine wave inverter and it runs everything I throw at it fine.
    However I have a few questions. I live in Australia, 240vac @ 50hz, and I
    have a small multimeter that has a HZ measuring function. when I put the
    test probe in the power outlet at home, it shows a rock steady 50 hz. When
    I put it in the inverter, is show something like 60 khz.

    When I have an AC/DC adapter (for a laptop) attached to the power point, and
    I put the Hz probe on the 12 volt output it shows 50 hz?? (Even though this
    is the DC end of the adapter)

    But when I use the AC/DC adapter on the inverter, the DC output also shows
    60 Khz.

    I would love someone with technical knowledge to explain this to me... when
    I test the inverter on an oscilloscope, it shows a nice clean 50 hz sine
    wave, even though the multimeter show 60 khz.

    I emailed the manufacturer of the inverter and this is his reply...

    HI ROB


    THE SINE WAVE PRODUCED IN THESE TYPES OF INVERTERS IS PRODUCED USING HIGH
    FREQUENCY PULSE WIDTH MODULATION (PWM) TECHNIQUE. IT IS NOT 100 % SINEWAVE
    BUT HAS APPROX. 3% THD. I AM NOT SURE HOW YOUR FREQUENCY METER WORKS. IT IS
    LIKELY THAT IT IS READING THE HIGH FREQUENCY PWM CONTENT. THE 50 HZ
    WAVEFORM MAY BE SEEN USING AN OSCILLOSCOPE.

    BEST REGARDS



    Now I have two more questions, even though everything seems to work well on
    the inverter, is there anyway that it is producing sub standard AC, and is
    there any way the 60khz coming through the dc end of the adapter could
    damage anything??

    One final question, does anyone know a brand of pure sine wave inverter
    that will definately produce AC power completely identical to a normal power
    point outlet? (IE something that would show up as 50 hz when tested with my
    multi meter)

    Thanks in advance for any advice.

    Rob
     
  2. So what you probably have is a 50Hz size wave, which is modulated
    by a 3% 60kHz waveform. Your scope is probably sync'ed on the 50Hz,
    and so the small 60kHz component probably only has the visible effect
    of defocussing the line. If your scope has the ability to filter the
    50Hz out from the trigger circuit, and you speed up the timebase by a
    factor of 10 and increase the y axis gain, you might see the 60kHz
    signal. (Might see it unstable even if you can't filter the trigger
    circuit.)

    As for why your meter changes reported frequency when the unit is on
    or off load... There's probably a 60kHz filter on the output of the
    inverter to help reduce the 60kHz THD. If part of this consists of
    a line inductor, that's only going to work where there's a load.
    I'm sure there is some way, but it's probably not very likely.
    It's going to be a much less efficient inverter I suspect.
     
  3. Rob

    Rob Guest

    Thanks for that explanation, It does produce a nice clean sine wave on the
    scope, and there is no percieved noise when used on radios or tvs, so I
    guess its ok.
     
  4. Rob

    Rob Guest

    Thanks Andrew, I have nothing more than a hobbyists understanding of all
    this, but your explanation helped. I did test it under load and it does
    indeed show 50 hz..

    Cheers.

    Rob
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-