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laptop with inverter

Discussion in 'Hobby Electronics' started by Heywood Jablome, Jun 19, 2005.

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  1. I have a 300W square wave inverter. Is it safe to use it with my laptop that
    uses a switchmode power supply?

    I have tried it with a lower power 1A 12V switchmode power supply and there
    is a notiseable buzz coming from the switchmode power supply when it is on
    the square wave. It is silent when used on a sine wave.

    I don't want to damage the laptop or power supply. As I will be using it
    only for 1 day, I don't want to buy extra equipment if I don't have to.

  2. w_tom

    w_tom Guest

    The are also called computer grade UPSes - because they can
    output square waves (modified sine waves) with so much
    harmonics as to even damage some small electric motors. But
    since computers are so resilient, then that 'dirty' UPS
    output (only when in battery backup mode) will not harm
    properly constructed electronics.

    As noted elsewhere, those square waves simply recharge front
    end electrolytic capacitors typically to 320 volts DC. Then
    the power supply sips electricity from those capacitors to
    operate the computer. Those electrolytic capacitors will
    remain charged whether the incoming AC is a sine wave or a
    square wave.

    In addition, minimally sufficient power supplies will also
    contain line filters. Although intended to keep RF
    interference inside the machine, those filters also make that
    square wave more sine like - just another layer between
    electronics and the 'dirty' UPS output.

    Meanwhile, a UPS may output 'dirty' square waves only during
    battery backup mode. Most of the time, the UPS connects
    cleaner sine waves, direct from the AC mains, into the load.
    Those square waves only exist during rare battery backup mode.

    Some third party power supplies are so inferior as to be
    easily damaged. IOW essential features such as the line
    filter, sufficiently sized electrolytic capacitors, and other
    'cost cutting' measures could mean dirty UPS electricity
    causes power supply failure. Its not a problem created by the
    UPS. Its a problem created by bean counting computer
    assemblers who don't even have basic electrical knowledge; who
    purchase inferior power supplies only on price.

    Again, they are called computer grade UPSes for good
    reason. Electricity so dirty that it can even harm a power
    strip surge protector attached to its output. Called
    'computer grade' because computers must be a most resilient
    appliance connected to AC mains.

    An example: this plug-in UPS creates a modified 120 VAC sine
    wave. IOW it creates two 200 volt square waves with a spike
    of up to 270 volts between those square waves. Output not
    destructive to computers as even required by Intel specs and
    other industry standards. Just don't power other less
    resilient appliances (ie small electric motor) with this UPS
    when in battery backup mode.

    Meanwhile some laptops have another problem with that so
    dirty UPS output. Laptops monitor AC input and switch over to
    internal batteries if AC power does not measure sufficient.
    IOW some laptops running on a computer grade UPS will remain
    powered from batteries and not recharge laptop's internal
    batteries. This because of how AC voltage is monitored AND
    because that UPS (in battery backup mode) outputs square
  3. There is quite a debate about this going in the aus.computers forum. I
    suspect a square wave will be fine, unless someone could give me an exact
    reason why any particular component would fail under a square wave. I'll
    give it a go anyway.

  4. w_tom

    w_tom Guest

    How to read that hogpog discussion in aus.computers. Many
    are just posting claims without providing technical reasons
    why and without providing numbers. Heavily discount those
    posts. Go back to that discussion and weed out the myths: no
    supporting technical facts and no numbers. That entire
    discussion will break down into only a few useful posts.
  5. Poxy

    Poxy Guest

    I went through this a few months ago on behalf of a friend - he ended up
    using a Jaycar square wave inverter. He used it to power an Apple powerbook
    for about 10 hours continuously (it was doing time-lapse capture) with no
    ill effects.
  6. w_tom

    w_tom Guest

    This is an example of the point I last posted. Provided was
    an example that by itself does not constitute a fact. Alone,
    it tells us nothing useful. However combined with underlying
    concepts and numbers, only then would the post have provided
    definitive information. For example, what was the inverter
    output voltage? AND what does the Apple power supply claim as
    its input voltage limits? Those numbers must be printed on
    each appliances. What is its AC input voltage rating?

    A Powerbook powered by a 120 volt inverter. The Powerbook
    input voltage rating is what? 90 VAC to 265 VAC? That is the
    point. Numbers are missing in so many posts in that other
    newsgroup; making those posts useless. Numbers from that
    Powerbook would make Poxy's post so more useful.

    Poxy does provide one useful number. 10 hours without
    failure. If ten hours from a UPS, then it tells us nothing
    because the UPS only acts as an inverter when disconnected
    from AC mains. However 10 hours from an inverter powered by
    DC battery power does provide a useful number. Again,
    underlying numbers AND the underlying concepts - the theory
    behind the example - create useful facts. To know something,
    one must have both fundamental theory and experimental
    evidence. Poxy only provided one experiment that demonstrated
    little due to missing facts and numbers.

    However, previously posted was an example of a 120 VAC
    inverter rated for computer use (computer grade). Two 200
    volt square waves with a spike of up to 270 volts between
    those square waves. A 120 volt computer should be powered by
    this modified sine wave without damage. That 120 volt
    computer rated to operate anywhere from 90 to 130 VAC.
    Without these numbers, then my previous post provided little
    useful information.
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