PFC in car amplifier

[zigzagflux]

You have just described a power supply with WAY too little capacitance in its input and/or output busses. The inductor won't fix this problem, but this wasn't the intent of the inductor in the first place.

The statement about an inductor being a series element is science, not opinion.

The opinion you stated wasn't about an inductor being a series element. It was your statement that "placing it at the battery side or inside the amplifier makes no change at all." That is an opinion.

 

[Eva]

http://www.diyaudio.com/forums/showthread.php?s=&threadid=111566

In this amplifier, input EMI filter inductor is 5uH, input capacitance is 4400uF and total rail capacitance is 9400uF. These values are similar to the ones found in commercial amplifiers. This results in a 500Hz cutoff (approx.) and strong AC below that frequency flowing through the 12V line.

Have you ever developed a car amplifier from scratch? You could learn a lot in the process.

 

[Clipped]

so if a PFC is for AC, can it be used in the output or predrive section of an amplifier? maybe somewhere in the feedback loop?

seems like an amplifier would benefit with having the current and voltage in phase with each other at the outputs.

im just guessing...please dont hit me. (i dont even know what a PFC is) lol

 

[zigzagflux]

Yep, too little capacitance.

 

[theAnonymous1]

Yep, too little capacitance.

Input, output, or both?

Is (8 x 3300uf) = 26,400uf input and 10,000uf(per rail) output "enough"?

BTW, with a ~500w load I only measure 54mv voltage drop across the input inductor I added.

 

[Eva]

so if a PFC is for AC, can it be used in the output or predrive section of an amplifier? maybe somewhere in the feedback loop?

seems like an amplifier would benefit with having the current and voltage in phase with each other at the outputs.

im just guessing...please dont hit me. (i dont even know what a PFC is) lol

PFC is only advantageous for AC mains, it's a kind of switching power supply with DC output (pseudo-regulated) and and AC input that simulates a resistive load to the mains line.

The only thing that this has in common with car amplifiers is just the need to control how much high frequency AC current is allowed to flow through the 12V line. Wiring inductance is evil sometimes.

Input, output, or both?

Is (8 x 3300uf) = 26,400uf input and 10,000uf(per rail) output "enough"?

BTW, with a ~500w load I only measure 54mv voltage drop across the input inductor I added.

You will almost always get the cutoff frequency on top of the midbass range, so all bass and midbass AC current will flow through the 12V line. This is unless you use huge non-practical capacitances and inductances. Remember that Fc=1/(2*3.1415*sqr(L*C)) so C or L have to be increased *four* times in order to halve the cutoff frequency.

Don't trust a multimeter when measuring complex waveforms, always use an oscilloscope to see the actual mess. Conventional (non-true-rms) multimeters in AC mode are only accurate measuring continuous 40-400Hz sinewaves.

 

[theAnonymous1]

You will almost always get the cutoff frequency on top of the midbass range, so all bass and midbass AC current will flow through the 12V line. This is unless you use huge non-practical capacitances and inductances. Remember that Fc=1/(2*3.1415*sqr(L*C)) so C or L have to be increased *four* times in order to halve the cutoff frequency.

Don't trust a multimeter when measuring complex waveforms, always use an oscilloscope to see the actual mess. Conventional (non-true-rms) multimeters in AC mode are only accurate measuring continuous 40-400Hz sinewaves.

Is there any benefit then to adding a very large cap, say >1F, to the input of the supply(for filtering purposes)? You know the kind kids put in their cars becuase it will give them an extra 10,000w boost.

 

[lumanauw]

Hi, theAnonymous1,

Is there any benefit then to adding a very large cap, say >1F, to the input of the supply(for filtering purposes)? You know the kind kids put in their cars becuase it will give them an extra 10,000w boost.

There's a patent about big cap bank, #7239206

Hi, EVA,

I don't understand about PFC. Why it has to boost the voltage first?

 

[theAnonymous1]

There's a patent about big cap bank, #7239206

I hate reading patents; every other word is "said". A bit annoying.