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In Reply to: Re: cap break-in posted by kurt s on March 22, 2007 at 07:57:22:
Careful about emphatic statements. Power factor correction should always be handled carefully.For most of us, the small capacitance we place on the 120V line is so small, those VARs feed into the rest of our household load, and never find their way to the utility. If we add enough capacitance to actually inject VARs back to the utility grid, we would find ourselves with a few hundred uF of capacitance (that's a lot of motor runs). In case you are thinking, YEAH, be aware of this:
To switch power factor over to a leading condition really requires capacitors on the AC line, not in the post-rectification stage. If you add 500uF of capacitance to your DC bus, you are not improving the power factor as seen by the utility significantly. What you are doing is adding a lot of harmonics, which are not friendly to just about everything. Combine with that the high cost and lack of chassis real estate, and there is no motivation to add extra DC capacitance over and above what the B+ ripple spec requires.
Adding capacitance across the AC line will definitely improve your power factor, and enough will go leading, injecting VARs out. However, this does very little to the performance of the amp's power supply. You only give the utility what you pay them to do.
A greater caution is that with the exporting of VARs, you get a corresponding rise in terminal voltage. That is, you may have 118V at your panel, and 124V at your capacitor terminals, depending on how much capacitance you are dealing with. This voltage rise, in combination with potential harmonics, are the primary reasons for caution in power factor correction.
Of course, if we're just talking about throwing a couple of motor runs across the line for break in, you won't affect much, and probably won't put out a single VAR to the utility, so this rambling may be a waste of typing. Just wanted to clarify that...
"People are actually encouraged to put all the capacitance they can on the power supply mains by the power company"
is not a true statement. I would suspect they would discourage it, so they are not responsible for any equipment damage you might cause. As well, industrial customers are often on different distribution systems, so the utility really doesn't need residential VARs. (Here in Wisconsin, most residential = 8.32 kV, industrial = 24.9, 13.2, and 4.1 kV). If you were another industrial customer, that's another story.
I suppose running your cap a little high in voltage could be advantageous for break in. But if the purpose of the cap is to run DC, I question the use of AC for break in. In general, I question the use of break in at all. Capacitors might be my only acception. Don't even get me started on speaker wires...
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Follow Ups
- Not recommended - KurtP 09:40:20 03/22/07 (1)
- Good points. - kurt s 10:48:40 03/22/07 (0)
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