Re: Generators and switch mode power supplies.

On Sun, 08 Feb 2009 15:57:14 +0000, Nobody <nobody@xxxxxxxxxxx> wrote:

On Sun, 08 Feb 2009 23:30:44 +1100, Sylvia Else wrote:

One thing to consider is that computers are a bad load
to a generator. As a rule of thumb you need a generator with at least
twice the VA rating as the total VA rating of all computers. Otherwise
the generator cannot keeps its rpm constant (starts speeding up and
slowing down).

I assume that's related to the harmonic load represented by switch mode
power supplies.

I assume that was referring to the variation in power consumption between
busy and idle.

Circuits for significantly improving the harmonic performance have been
around for a decade, but I suppose little will happen until legislation
requires their use.

EU legislation has required their use for some time (2001, AFAICT).
Specifically, most power supplies above 75W must comply with
IEC/EN61000-3-2, with computer PSUs conforming to class D.

In practice, this means that a typical ATX PSU starts with a boost
converter whose current waveform is roughly sinusoidal, and in phase with
the line voltage.

Although this isn't required in the US, I would assume that most PSUs will
have been designed to meet EU standards anyhow (cf RoHS).

FWIW, an application note on PFC:

http://www.onsemi.com/pub_link/Collateral/HBD853-D.PDF

Power factor correction and harmonic suppression are two different
things. It is just convenient that typical PFC circuits also reduce
harmonics.

.

Relevant Pages

  • Re: Generators and switch mode power supplies.
    ... considering buying a standby generator. ... One marketing point of some of the inverter based models is their suitability for 'sensitive electronics' with computers given as an example. ... But given that computers invariably use switch-mode power supplies, are they actually going to care what waveform they see - from square wave thru 'modified sinewave' thru pure sinewave? ... I assume that's related to the harmonic load represented by switch mode power supplies. ...
    (sci.electronics.design)
  • Re: Generators and switch mode power supplies.
    ... As a rule of thumb you need a generator with at least ... twice the VA rating as the total VA rating of all computers. ... with computer PSUs conforming to class D. ...
    (sci.electronics.design)
  • Re: Generators and switch mode power supplies.
    ... considering buying a standby generator. ... One marketing point of some of the inverter based models is their suitability for 'sensitive electronics' with computers given as an example. ... This appears to be based on the fact that they'll provide a consistent sinewave output. ... twice the VA rating as the total VA rating of all computers. ...
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  • Re: Generators and switch mode power supplies.
    ... considering buying a standby generator. ... based on the fact that they'll provide a consistent sinewave output. ... But given that computers invariably use switch-mode power supplies, ... twice the VA rating as the total VA rating of all computers. ...
    (sci.electronics.design)
  • Re: Generators and switch mode power supplies.
    ... considering buying a standby generator. ... based on the fact that they'll provide a consistent sinewave output. ... But given that computers invariably use switch-mode power supplies, ... twice the VA rating as the total VA rating of all computers. ...
    (sci.electronics.design)