50 Farad 18 volt capacitor. Yoicks!
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dkemppai
diyAudio Member

Join Date: Nov 2002
Location: Michigan, USA

Quote:
 Originally posted by zx3chris Lesson 1 Ok powertrip how about we have a discussion in basic electrical theory. At the end of this thread...

Whoa, sorry couldn't spare the time to read all the way through the end.

Two questions? Did you take into account the ESL of the cap, or only ESR? How about the duty cycle and switching frequency of the power converter in the amplifier?

Anyway... ...my thoughts on the subject.
A power converter running at 50 Khz with a 50% dutycycle during peak demands will draw current much faster than most large capacitors will be able to supply it. This can be a misleading factor when measuring the input voltage to the amp. When the switching converter actually draws current, series inductance and resistance in the power supply to the amp can cause voltage drops, that will not be detected by the by most DMMs.

I have measured input voltage on amplifiers, with scopes and DMM's. At times the DMM a will read 11 volts (Average), when the input voltage is actually only 9 volts (steady state low of the waveform) when the switcher is actually drawing current. This is because the current draw from the battery is a high frequency current draw (50Khz or so) In this case, the capacitor would need to be fast enough to supply current at the switching frequency, not the music frequency. (40 samples per second will probably not catch the transients)

Most large can type capacitors don't do much good, because they cannot supply power at the frequency of the swithcing currents. The best solution is to add more capacitance to the output side of the switcher just before the input to the amp.

-Dan

 23rd May 2003, 02:24 AM #17 mikee12345   diyAudio Member     Join Date: Nov 2002 Location: NZ ooohh very interesting i read the first two,il come back for the rest later.. makes sense..lol at the dent in the exhaust pipe story.. i need to know the conclusions of this all,il read when i ahve the time :-D:-D cos everyone in car audio seems to think a huge cap makes it much more better,and i dont buy/do things for no proven reason
 24th May 2003, 04:21 AM #18 Sawzall diyAudio Member   Join Date: Jun 2001 Location: Alexandria, VA USA Great read zx3cris..thanks for posting it. What was the source for this? While I know you said that it was written for folks who know nothing, I get the feeling either they were supposed to know it, or thought they did. Secondly, If this was open, it would be neat if you could get permission from the author to put it in the wiki. Then folks could just point to it when the next newbie came by asking about "stiffening caps".. Finally, it was great to see someone actually spend that amount of time to teach the mostly unwilling it seems. I remember my days trying to sell audio. I was not any good at it since I could not let my ethics go so low as to sell useless stuff like these caps. (or any of a thousand other snake oil items..)
 25th May 2003, 05:51 AM #19 zx3chris diyAudio Member   Join Date: Oct 2002 Location: south amboy nj this was posted years ago in the carsound.com forums.. richard clark (electrical engineering who worked in audio for years and years, and has quite a history---look him up), wrote it.. he has a forum just for him on that site, and will occasionally answer questions so long as they havent been asked 1000s of times.. the oringal post had 100s of replies--i just cut out what he said, and composed that.. u can put it whever it can be useful--its a great explanation in my opinion ;D -chris
 25th May 2003, 08:31 AM #20 Cradle22   diyAudio Member     Join Date: Jan 2003 Location: Dortmund, Germany Hi! Well, OK, I understand a lot of the explanantions, and generally I despise everything in the HiFi sector which even faintly smells of "Voodoo", but how do you explain this: Without my 1F (not those overrated 10+F thingies) cap my lights are actually flashing like a strobo during strong bass bursts. With the simple addition of the cap (and now here is one thing which I think was not mentioned: the cap has to be put NOT MORE THAN 30cm (cable length, that is) from the main load, in this case my bass amplfifier), the lights stopped flashing entirely! And while this cap got older, the flashing grew stronger again. Two months ago I exchanged it with a new one, and the flashing was gone again... That can't be just my imagination, so physically adding such a cap must make a difference. Just my 2 cents... Bye, Arndt __________________ ************************ A Sacrifice For Freedom

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