Re: Generators and switch mode power supplies.

JosephKK wrote:
On Sun, 08 Feb 2009 23:30:44 +1100, Sylvia Else
<sylvia@xxxxxxxxxxxxxxxxxxx> wrote:

Nico Coesel wrote:
Sylvia Else <sylvia@xxxxxxxxxxxxxxxxxxx> wrote:

Given the parlous state of Australia's power systems, I've been 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.

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?
Not really. A computer doesn't care much as long as the voltage is
within range. 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.

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

Sylvia.

May not have happened yet down there, but has been around for about 2
decades in the US now.

Given that PC power supplies are essentially a world-wide commodity item, I'd have thought that Australia would have inherited any improvements mandated in other jurisdictions, even if there were no local regulations.

But I knocked together a current-transformer, and looked at the current drawn by three PCs and a monitor, (being the input current to a switch-over type UPS when it's not operating in backup mode). What I see seems to be what an un-harmonic-corrected power supply would draw.

Sylvia.
.

Relevant Pages

  • 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. ... most power supplies above 75W must comply with ...
    (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. ...
    (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. ... The class D limit of 3.4mA/W for the third harmonic means 1.7A for a 500W PS, which would be drawing only just over 2A at the fundamental. ...
    (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, ... Doesn't seem an exactly onerous requirement. ...
    (sci.electronics.design)
  • Re: UPS Suggestions
    ... We have a lot of computers here, ... Once we do that there is close to 24 hours of power ... generator can support a refrigerator and freezer easily. ... A transfer switch allows you to isolate circuits and switch them from ...
    (Fedora)
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