In article ,
John Rumm writes:
On 19/04/2014 01:09, Uncle Peter wrote:
On Sat, 19 Apr 2014 00:43:30 +0100, John Rumm
wrote:

On 18/04/2014 11:01, Uncle Peter wrote:
On Fri, 18 Apr 2014 10:44:39 +0100, Andrew Gabriel
wrote:


Thanks, that's the answer I was looking for. Although does that also
apply when taking power off the peaks of the waveform for ****ty
switch mode supplies?

Yes. They generate 3rd-harmonic distortion, which can be bad in large
quantities because it adds together in the neutral line, rather than
canceling out between phases.

And I guess there's no way to cancel a harmonic like you can shift
normal PF with a capacitor.

Its not easy once the harmonic content has been created. The PFC built
into modern SMPSUs will suppress the creation of it by spreading the
duration of the current draw by the PSU - rather than just concentrating
it at the peak of the voltage waveform.

These are modern SMPSUs, just very cheap ones (about half the price).

Anything over 75W is required to have PFC these days...

and for electronic ballasts for lighting, anything over 25W, including
CFLs with integral ballasts.

--
Andrew Gabriel
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