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In Reply to: RE: How large can the capacitance be in parallel AC filter? posted by dave789 on November 28, 2014 at 18:48:56
The magnan cable website. Interesting. There are many who look at these caps as modifying the power factor of the affected line.
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I googled, but could not find magnan cable home page.
I guess because caps were used for power factor correction for motors and inductive loads. Caps work for that. But the kind of power factor problems that audio gear presents (anything with a power supply basically) is a different kind of problem - not the relatively simple issue of the current and voltage being just a bit out of phase, but the problem is that the current is drawn in short bursts, rather than uniformly over the whole cycle (non-linear). Caps can't fix this problem.
The line itself doesn't have a power factor, as power factor is a function of a whole circuit, and revolves around how the load consumes power.
"the problem is that the current is drawn in short bursts, rather than uniformly over the whole cycle (non-linear). Caps can't fix this problem. "
I think large caps can reduce the effect from short burst current draw: some of the current is drawn from the cap. But I do not know how a large cap in an external box AC filter can be safe for human beings.
I was talking about power factor correction. And caps can't fix this. In fact the caps that follow the diodes in a power supply are what *cause* the power factor problem; the bigger the caps, the worse the power factor (roughly speaking), as the bursts that the AC is higher voltage than the caps (and hence charging them) is shorter.
The bigger the DC caps, the worse the power factor.AC caps, however, can make the power factor better.
Reducing THD in the AC waveform, caused by current surge by AC to DC converters, is also power factor correction in broad sense.
"The capacitance be in parallel AC filter" in my original post was the capacitance of AC capacitor.
Edits: 12/13/14
I maintain that putting caps across the AC line is not really going to affect the power factor a whole lot. Not without an inductor there as well. Sure, a little bit. But as the calculations above have shown, you can't really have a very large cap directly across the AC, ~100uF max thereabouts. This isn't typically going to affect the PF much.
Actually this is something I'd been thinking about for some time : why does nobody make audio gear with active power factor correction? (Correct me if I'm wrong) Passive correction is not very efficient, even when done properly with inductors and capacitors you only normally get up to 0.75 or thereabouts.
Active correction can get you a PF up to almost 1. But as with most engineering, there are tradeoffs, the most significant of which for us audiophiles is the EMI that such switching devices produce. Look up "duel stage active pfc" for example.
MIT made a z terminator plc. Quite effective though analysis was difficult because boards were covered in black resin. I believe it was a progressive PF corrector.
What is a progressive PF corrector?
OK I admit I'm guessing. Z stabilizer Unit seemed to have three parallel boards. Exact values unknown because of the black resin wash. Worked very well and I still use mine. Plug in anywhere but works best closest to components. Doesn't seem to interact with PLCs. No visible inductors but resisters and assorted . curiously plugging in unit occasionally causes a small spark at the duplex. No large visible caps though not semi conductors
Sound sort of smooths out. Quieter background ,better micro dynamics with better detail. All in all better musical control of system
Of course YMMV
What is a progressive PF corrector?
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