Re: [neonixie-l] SMPSU efficiency

Michel van der Meij Mon, 07 Jan 2013 15:14:49 -0800

Absolutely correct John, it would only make sense (in my case) if there was no phase shift between voltage and current. Something I haven't measured yet....

Michel

on Jan 08, 2013, John Rehwinkel <[email protected]> wrote:

> However, you can only use the average values if either the tube
> voltage or tube current is constant; in my case this is not so. So I
> would say I need to use the RMS values of tube voltage and tube
> current. If I measure these with a scope, I come to 113V RMS and
> 3.73mA RMS. This would then result in a 96% efficiency!!!
>
> This measuring must be correct, right?

The measuring is probably correct (subject to the definition of RMS when largish crest
factors are involved). However, the math is invalid. To compute the correct power draw
with AC waveforms, you have to multiply the instantaneous voltage by the instantaneous
current moment by moment, and sum up all the products over at least one full cycle.

Even with plain old sine waves, just multiplying RMS voltage by RMS current can be
misleading, due to phase differences. That's the real difference between VA and watts.

- John

--
You received this message because you are subscribed to the Google Groups "neonixie-l" group.
To post to this group, send an email to [email protected].
To unsubscribe from this group, send email to [email protected].
For more options, visit https://groups.google.com/groups/opt_out.

--
You received this message because you are subscribed to the Google Groups "neonixie-l" group.
To post to this group, send an email to [email protected].
To unsubscribe from this group, send email to [email protected].
For more options, visit https://groups.google.com/groups/opt_out.

Re: [neonixie-l] SMPSU efficiency

Reply via email to