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huge parallel capacitor to the power cord: why bad?

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Posted on August 9, 2014 at 16:58:21
dave789
Audiophile

Posts: 559
Joined: September 21, 2001

Why is nobody connecting a huge parallel capacitor to the power cord of an amp?

An amplifier with linear power supply draws current from the wall in the form of two short (mush shorter than half period of 60 or 50 Hz) pulses in one cycle of 60Hz (or 50Hz) AC power.

A mecanical analoge: a capacitor in parallel to an amplifier's AC power input is like a fly wheel connected to a piston engine.

To me this parallel AC capacitor connection looks like a cost effective sound quality improvement, but I saw nobody doing this. Why?

 

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Furman 'powerfactor' powerconditioners use a capacitor to 'stiffen' the AC lines. nt, posted on August 9, 2014 at 23:04:41
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Many commercial power conditioners use it., posted on August 10, 2014 at 09:41:42
carcass93
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Posts: 7181
Location: NJ
Joined: September 20, 2006
 Problem is, the effect is not always positive (depending on equipment), and pretty much always negative when it comes to power amplifiers.

 

RE: huge parallel capacitor to the power cord: why bad?, posted on August 10, 2014 at 10:37:32
AbeCollins
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Location: USA
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Contributor
  Since: February 2, 2002
Because the 'huge' capacitors belong on the DC side of the power supply where they are most effective at smoothing 50/60Hz ripple after the rectifier.

It wouldn't make sense to try to 'smooth' the 50/60Hz AC before the power supply transformer as the transformer is designed to work from a 50/60Hz sinewave.

What you will often find are smaller capacitance / higher voltage capacitors on the AC primary side of the transformer to help filter higher frequency noise and transients (spikes) but not to 'knock down' the 50/60Hz sinewave peaks.

And what's the relevance of that green 3-way adapter pictured in your post?



 

Do some research, posted on August 10, 2014 at 13:22:13
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 on power factor capacitors. The issue becomes a bit more complicated but most of your answers will be answered and then some. Also check out Magnan cables website.

 

RE: huge parallel capacitor to the power cord: why bad?, posted on August 11, 2014 at 18:07:23
dave789
Audiophile

Posts: 559
Joined: September 21, 2001

"Because the 'huge' capacitors belong on the DC side of the power supply where they are most effective at smoothing 50/60Hz ripple after the rectifier.

It wouldn't make sense to try to 'smooth' the 50/60Hz AC before the power supply transformer as the transformer is designed to work from a 50/60Hz sinewave.
"

If you increase the capacitor on the DC side, the current pulse from the wall becomes narrower in time and higher in peak current value.

An ideal sinusoidal voltage source will have no problem with this, but a real world AC power will have a problem. That is why I consider huge AC capacitor.

 

PFC Correction, posted on August 12, 2014 at 00:00:20
pictureguy
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Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Is a fact of life in some large manufacturing plants where if the power factor presented to the electric utility drops to low, they get hit with a surcharge.

PFC correction may pay for itself if the correction gets the plant closer to looking like a resistor to the electric company and the surcharge was high in relation to the cost of the modification.

As for home use? Kooky.

Don't forget, you USE VA and get billed for WATTS


Too much is never enough

 

RE: PFC Correction, posted on August 12, 2014 at 00:29:56
unclestu
Dealer

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 Not so. The EU ,IIRC, has mandated that PFC be applied on all electrical appliances.

 

RE: PFC Correction, posted on August 12, 2014 at 09:57:18
pictureguy
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Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Another crazy law.
Do you know the threshold needed for the application of PFC? Here in the states, the Surcharge from your power company applies at some PF level…maybe 0.9 or worse. Why would it be mandated that a device with a PF of OVER 0.9 need PFC? Only large consumers of electricity are given such surcharges. Home owners? Not Yet, but it may be coming.
For small appliances it might take more to impliment than is saved.

Now that we have 'smart meters' I have something to look forward to. Getting billed for ACTUAL power used, not just watts!

I can think of another way to make such law and still give choices. When something is sold, it is taxed on efficiency. Higher efficiency=lower tax. Kind of like VAT, only for power. So, just like in the states you can still buy poor fuel economy cars, you just pay the Gas Guzzler Tax.. The lower the PF, the higher the tax.

Any reports on audio equipement so equipped? Sound better or worse?

Too much is never enough

 

REGULATIONS:, posted on August 12, 2014 at 10:15:47
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Here is a list of rules.

They talk about 'harmonics'.
Too much is never enough

 

RE: huge parallel capacitor to the power cord: why bad?, posted on August 12, 2014 at 11:55:42
AbeCollins
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Posts: 46280
Location: USA
Joined: June 22, 2001
Contributor
  Since: February 2, 2002
 A mecanical analoge: a capacitor in parallel to an amplifier's AC power input is like a fly wheel connected to a piston engine.

So is an inductor in series. LCR filters on the primary side are not uncommon.

What are you trying to accomplish?



 

PFC numbers?, posted on August 12, 2014 at 19:07:13
pictureguy
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Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I've got a PFC question.
Lets say the basic device WITHOUT PFC draws 1amp at 120v to yield 120 watts / P=IE. RIght so far?
Let's further say the Power Factor is 0.8 which turns into 150VA.
You are getting BILLED for Watts and USING VA.

Now, let's say you add PFC to the device in the form of either a modified power supply OR an external PFC 'device'.

What is the result…..You look like a resistor which draws 1 amp = 120 watts, or do you NOW draw 1.25 amps which results in 150 watts? If you are powering an amp, you're still going to want the same power OUT.


Too much is never enough

 

RE: huge parallel capacitor to the power cord: why bad?, posted on August 13, 2014 at 18:46:33
fantja
Audiophile

Posts: 15518
Location: Alabama
Joined: September 11, 2010
 I use a Richard Gray power line conditioner in my A/V system. I believe that there is parallel capitor use.

 

RE: Your question is flawed, posted on August 15, 2014 at 10:35:34
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 First off, watts = power factor × amps × volts.

So when you say 1 amp at 120 volts equals 120 watts.....that would only be true with a power factor of 1. If you had something that drew 1 amp at 120 volts with a power factor of 0.8 then it would be 96 watts.

The problem for the power company is it must size wire to deliver the 1 amp at 120 volts despite the fact that they bill for 96 watts (because of a power factor of 0.8). If you "corrected" the power factor to one then you would draw less current (your volt amps would go down).

BTW, 0.8 is a rather typical power factor. In fact most generators are speced assuming that power factor.

Hope this helps.

 

RE: Your question is flawed, posted on August 15, 2014 at 13:37:15
pictureguy
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Posts: 22597
Location: SoCal
Joined: October 19, 2008
 That is opposite of what I observe.
I have a 4' fluorescent tube near my desk.
As it warms, the PF rises.
Here are the 'cold' numbers:
House voltage=117.2 (Hot summer days drops the voltage from 118+)
I=0.34
P=31
VA=38
PF=0.81

The 'advert' calls this a '40 watt tube'. I can't kick.

When it warms, the PF goes UP slightly.

As I understand it, YOUR formula is wrong. Watts = IE VA=watts x 1/PF
The 1/PF results in a number >1 which when multiplied by watts gives VA, which as I understand it is ALWAYS the larger of watts VS VA.

I think the above is right:
PF is always <=1 and watts always <= VA P (in watts) = VA for resistive loads only.
Too much is never enough

 

RE: Your question is flawed, posted on August 15, 2014 at 14:38:14
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 The OTHER can of worms here is that AMPLIFIERS vary in their ability to drive reactive loads.

Some amps may test identically into a resistor PF=1, but when PF drops, fail to deliver. Some speakers with huge phase angles at impedance minima are the WORST offenders, with only about 1/2 the 'power' available for 'delivery'. PF=Cos. phase angle

Also, a 'device' can draw 1 amp / 120 volts at ANY PF. The only thing which will vary is that the VA will go UP as PF Drops. And it will STILL 'look' like 120 watts.

I think it is a reasonable idea for the power grid to be able and DESIGNED to handle a PF <=1. I don't have any heartburn with that idea.
Factories are charged, in some locations, for large power draws at Too Low a PF. (Surcharge)

Too much is never enough

 

RE: What?, posted on August 15, 2014 at 15:35:35
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 I'll deal with the second part first.

As I understand it, YOUR formula is wrong. Watts = VA * PF
Watts does equal volt amps times power factor. That is a fact.

PF is always <=1 and watts always <= VA
The absolute value of power factor is less than or equal to one. Watts is less than or equal to volt amps. Volts time amps is apparent power. To know power factor you need to also know real power (measured watts).

Too much is never enough.
Totally depends:)

Your florescent lamp situation would need to be better defined. I am curious how you are arriving at a number for power factor. Do you have a watt meter designed for use on non linear loads?

It bears mentioning that a low power factor can be caused by reactive loads like inductors and capacitors. It can also be casued by non linear loads like a flourescent ballast or a rectifier in an amplifier. The latter are different and create harmonic distortion making it hard to state actual power factor. You might call the first a "displacement power factor" and the second a "distortion power factor".

 

RE: What?, posted on August 15, 2014 at 16:23:18
pictureguy
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Posts: 22597
Location: SoCal
Joined: October 19, 2008
 My formula, corrected, is correct.
And we said the SAME thing….about what is larger, VA or Watts.

Now, I use a Kill-A-Watt meter. Cheap, fast, easy and does NOT distinguish between displacement PF and Distortion PF. Accuracy? Who knows? Repeatability? Also who knows? It DOES seem reasonably repeatable when measuring the same device many times over several weeks.

I posted a paper from the EU about PF and its measure and the mandate for PFC on many devices. A few exceptions were made, but they talked a LOT about DPF (distortion PF).

My original question still stands, however, if you have a Non-Resistive load (PF<1) and you apply external PFC, do Watts to UP or does VA come DOWN? If VA comes down, you are ahead, If Watts goes UP, you might make your 'strain' on the power grid somewhat less, but are not really ahead from an actual power use viewpoint. In either case, the power grid is slightly better off.

And from our FWIW department, since you are both interested and knowledable, here is a link to a neat way to measure amplifier power. They measure at several fixed impedances AND from Inductive to Reactive at several points. The final 'graph' is very descriptive of an amps performance when things get weird. Not the audio graph link, but close enough.


Too much is never enough

 

RE: What?, posted on August 15, 2014 at 16:33:21
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I believe that PF is always <1 because it is the COS of the angle of displacement between voltage and current. That will ALWAYS be <1, and I don't think we need to apply Absolute Value to make it so.
Can there be a PF >1 or a negative number? I know at a displacement of 90' NO power is delivered and at 91', you are back to essentially 1' of displacement.

OH! I'm sure I could get a better PF measure if I had the right instruments. I don't even have a true RMS DVM or a scope. I might have an ancient Simpson Senior Voltohmist out in the garage in storage, but haven't used it in a long time.
Too much is never enough

 

RE: What?, posted on August 15, 2014 at 18:10:30
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 if you have a Non-Resistive load (PF<1) and you apply external PFC, do Watts to UP or does VA come DOWN?

Volt amps goes down. Current is used more efficently. That is what the power company cares about and why they charge for poor power factor.

 

RE: What?, posted on August 15, 2014 at 19:18:03
Russ57
Audiophile

Posts: 3754
Location: South Florida
Joined: November 16, 2001
 Power factor can range from negative 1 to positive 1. It is the ratio of real and apparent power. A purely resistive load would have a power factor of 1. A power factor of -1 would be something that is normally a load but is instead generating power power back into the source.

It is hard to communicate some concepts. Some things are vectors which can be added/multiplied but they are done differently. Other things are only true in certain conditions. When it is "displacment power factor only" the power factor is the cosine of the angle between the current and voltage sinusoid waveforms. When it is distortion all bets are off:)

It is even more confused by certain conventions such as calling leading/lagging power factor as +/-power factor. But rest assured, despite leading publications to the contray, there is such a thing as negative power and negative power factor.

You might find this link interesting....best I could do on a quick search.

http://www.cui.com/catalog/resource/power-factor.pdf

 

RE: What?, posted on August 15, 2014 at 20:18:55
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Ok, good.
Now, for those who can test such things, would such PFC effect the sound from the amp? Better? Worse? or perhaps just 'different'?
I think most audiophiles could care less about the electric bill, especially those fans of pure class 'a' or 'high bias' designs like Pass and a few others.
Too much is never enough

 

RE: What?, posted on August 16, 2014 at 00:39:47
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Power back into the source, eh? I'll run this thru the brain cell while keeping damping factor in mind. The perfect amp, with ZERO back resistance with the devices ON, should shunt all the back EMF to the driver which produced it in the first place, no?

I'll read the link tomorrow. I'm beat and expecting COMPANY which means I've work to do in preparation.

I'm even missing a meeting of my fellow planar enthusiasts who are having a small get-together tomorrow.
Too much is never enough

 

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