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Power conditioners and filters

Discussion in 'Electronic Basics' started by RR, Dec 14, 2005.

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  1. RR

    RR Guest


    Will a cheap filter clean up an AC waveform (remove most if not all noise)
    or do I need a real power conditioner?

    Any comments on the quality of the APC LE-1200I, which seems to be a real
    power conditioner at a reasonable price?

    I know I can buy one and look at the waveform to see if it's much improved,
    but I thought I'd run it past you experts. (Thanks again for your help on my
    other posts.)

    The background is as follows.....

    I've bought a diesel Generator Set for backup power, and today we actually
    had a 2 hour power failure. It was a great asset to have!

    I mainly use it for supplying our online (double conversion) UPS which power
    our computers.

    One UPS (the smaller one, of course!) handles the GenSet output fine.

    The main (larger) UPS goes into fault condition when I plug it into the

    I've worked with the UPS manufacturer and still have no resolution for this
    problem. I do have a workaround, which worked fine today, but it's an
    annoyance (I have to remove all load from the UPS - switch off the
    computers - then apply the input power then apply the load once the UPS has
    switched the inverter on).

    I know what *is not* causing the problem. It's not the voltage, it's not
    the frequency, and it's not the floating earth.

    I now believe it is the noisy waveform that the GenSet supplies. It provides
    a reasonably steady 54Hz and 240V, but the waveform is quite noisy. In
    particular, at peak voltage there is a 10-20% short-lived voltage drop.
    Thru the rest of the waveform there are notches or jitters.

    The theory is that the UPS tries to match the frequency between the inverter
    and the the mains (GenSet). The noise looks like very erratic frequency and
    this confuses the UPS and it goes into fault.

    All I want is a cheap filter or conditioner that I can place between the
    GenSet and the UPS and have it remove enough of the noise so that the UPS
    doesn't go into fault condition.

    The UPS manufacturer has been very helpful, but the conditioners they supply
    cost 6 times the APC one mentioned above.

  2. Guest

    Depends what kind of noise it is. RF will be removed with a simple
    Why is your earth floating?

    These are caused by the capacitors in smps charging, you cant do much
    about them without spending lots of money.
  3. RR

    RR Guest

    From what I've read, any change to a sine wave (e.g. a square wave) can be
    thought of as many harmonics being added to it, esp high freq harmonics.
    But I guess this doesn't count as RF, does it?
    The GenSet provides a floating earth and the UPS *was* set for M.E.N. We
    converted the UPS to floating in case that was the problem. It wasn't.

    AFAIK, floating earth simply means the Neutral is not tied to the earth
    line. So, there's a potential between A-E and N-E which added together
    provides the mains potential between A-N.

    The earth wire is connected through the GenSet to a steel stake in the
    Do you mean that the *cheaper* power conditioners (such as the APC I
    mentioned) can't fix this in the waveform, or do you mean that no power
    conditioner can fix it?

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