First filter cap - Big or Small?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 15th August 2010, 11:37 AM #11 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders What little I think I know about power factor is to do with the phase difference between current and voltage. Industrial loads tend to be inductive and as you have said this uses current and develops current losses that are not directly related to the power consumed. I gather that capacitors can be used to bring the phase of the current closer to that of the voltage and thereby reduce the wasted I^2R current losses that are not power. But what is schem referring to? That statement seems to be something quite different, and Abrax seems to be going down the same route, by saying that capacitors make the problem worse. Explain what you are referring to. __________________ regards Andrew T. Last edited by AndrewT; 15th August 2010 at 11:39 AM.
abraxalito
diyAudio Member

Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Quote:
 Originally Posted by AndrewT What little I think I know about power factor is to do with the phase difference between current and voltage.
Yes, this is correct - the supply companies strongly prefer consumers to connect appliances with near to unity power factor - that means resistive loads are best.

Quote:
 Industrial loads tend to be inductive and as you have said this uses current and develops current losses that are not directly related to the power consumed.
Inductors draw current but very little power is consumed in the load. Suppliers suffer losses due to heating relative to the square of the current drawn, not relative to the power taken. They charge domestic consumers according to power, not current.

Quote:
 I gather that capacitors can be used to bring the phase of the current closer to that of the voltage and thereby reduce the wasted I^2R current losses that are not power.
If a company has loads which are mainly inductive, putting capacitors across the mains can improve the power factor. Inductors have lagging current, capacitors leading current. With the right value added cap, the leading can cancel the lagging so the result just looks near enough a resistor.

I am not sure about this, but I believe that industrial companies pay their electric bills according to VA, not Watts. Does anyone know to confirm this? If its true, then the company will pay lower bills by correcting their power factor.

Quote:
 But what is schem referring to?
He's saying a big cap used on the secondary of a transformer makes for a poor power factor - large current flow, larger stray fields and more heating in the transformer. So he's discouraging specifying too big caps on the secondary.

Any clearer now?
__________________
'The total potential here must be nothing less than astronomical.'
'Nothing less. The number 10 raised almost literally to the power of infinity.'

AndrewT
diyAudio Member

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by abraxalito ..........He's saying a big cap used on the secondary of a transformer makes for a poor power factor - large current flow, larger stray fields and more heating in the transformer. So he's discouraging specifying too big caps on the secondary. Any clearer now?
no.
Quote:
 .Big capacitors worsen power factor considerably
I just cannot see with my understanding where that statement comes from.
__________________
regards Andrew T.

sreten
R.I.P.

Join Date: Nov 2003
Location: Brighton UK
Quote:
 Originally Posted by AndrewT no. I just cannot see with my understanding where that statement comes from.

Hi,

They are simply saying the short large peak rectified currents for an oversized
capacitor will cause more resistive losses than a "correctly" sized capacitor.

In a pre-amp / CD player this hardly matters, and CRC filtering can be used.
Small then Big in this case is poor due to the supply wiring AC ripple currents.

It does matter in high power applications, it not true that you "cannot
make the filtering capacitors too big", you can, causing excessive losses.

I agree with you though, power factor is not "conversion efficiency",
though this what is often meant when the term "power factor" is used.

Lots of wasteful resistive losses will actually improve "power factor",
but not "conversion efficiency" or "maximum supply power throughput".

rgds, sreten.

Last edited by sreten; 15th August 2010 at 02:02 PM.

 15th August 2010, 03:05 PM #15 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Sreten, are you saying that the use of the phrase "Power Factor" has nothing to do with what Schem is referring to? BTW, I started using psud many years ago. It clearly shows the short term current peak when voltage after the rectifier is above the voltage stored in the smoothing capacitor. That never confused me. I also know that most transformer manufacturers recommend a transformer de-rating factor when the transformer feeds a capacitor input filter. I have seen DF between ~65% and ~75% and that is what I use to determine the maximum continuous DC current that can be drawn from the smoothing capacitors. This usually comes out at ~half the maximum AC current. __________________ regards Andrew T. Last edited by AndrewT; 15th August 2010 at 03:10 PM.
 15th August 2010, 03:38 PM #16 Speedskater   diyAudio Member     Join Date: Sep 2002 Location: Lakewood, Ohio Somehow they seem to write about the DC power supply then about the AC power supply. It's hard to keep track. I thought that the original question was about main reserve supply capacitors and stage decoupling capacitors. But now I'm not sure. __________________ Kevin
AndrewT
diyAudio Member

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by Speedskater Somehow they seem to write about the DC power supply then about the AC power supply. It's hard to keep track.
somehow, I am coming to the conclusion that they cannot keep track either.
__________________
regards Andrew T.

abraxalito
diyAudio Member

Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Quote:
 Originally Posted by AndrewT I also know that most transformer manufacturers recommend a transformer de-rating factor when the transformer feeds a capacitor input filter.
I'd be surprised if it wasn't all trafo manufacturers. A capacitive load's power factor after rectification to some degree depends on the ripple voltage - higher ripple means better (higher) PF.
__________________
'The total potential here must be nothing less than astronomical.'
'Nothing less. The number 10 raised almost literally to the power of infinity.'

abraxalito
diyAudio Member

Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Quote:
 Originally Posted by AndrewT somehow, I am coming to the conclusion that they cannot keep track either.
If by any faint chance 'they' includes me, feel free to highlight the bits in my writing where you're getting confused. I realize my writing skills leave room for improvement in clarity
__________________
'The total potential here must be nothing less than astronomical.'
'Nothing less. The number 10 raised almost literally to the power of infinity.'

AndrewT
diyAudio Member

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by abraxalito A capacitive load's power factor after rectification ........................ higher ripple means better (higher) PF.
Quote:
 Originally Posted by abraxalito ........feel free to highlight the bits in my writing where you're getting confused.
you're last post has two quotes that confuse me.
__________________
regards Andrew T.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post Monjul Tubes / Valves 4 27th January 2010 01:53 PM underwurlde Power Supplies 20 27th August 2009 07:18 PM engels Tubes / Valves 5 29th January 2008 11:16 PM jarthel Power Supplies 20 20th October 2006 12:25 AM beppe61 Power Supplies 2 18th July 2006 06:46 PM

 New To Site? Need Help?

All times are GMT. The time now is 04:50 AM.