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Old 1st February 2007, 06:42 PM   #1
h_a is offline h_a  Europe
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Default proper design of pi-filter for Aleph 30

Hi folks!

When dimensioning the inductor vor this CLC-filter, how is it done properly? Here is a nice schematic, however it is for 180 000uF which is more than I want.

I'm more interested in 3x 22 000uF caps, so the inductor would go between the first 2 caps I think.

But how to calculate the proper inductor value?

3.9mH won't fit I think.

Any ideas?

Have fun! Hannes
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Old 1st February 2007, 06:55 PM   #2
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Old 1st February 2007, 07:00 PM   #3
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Old 1st February 2007, 08:00 PM   #4
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in my aleph 3 68000uF+1.2mH +68000uF

with good result supply ripple = 25mv ac

standard value are 2mH to 4mH

but inductor has resistance

air core = no saturation but maybe more resistance and heat

and magnetic induction in your aleph

i test my 1.2mH iron core for no saturation @ 10A

wire=no 16 resistance=0,15 ohm
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Old 2nd February 2007, 10:21 AM   #5
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Thanks for all replies!

Well. so is there no optimum value? Since capacitors cause a phase shift, I thought there's an optimum inductor value that shifts the phase of the remaining ripple perfectly back to 0 - which I guess should be the best.

What makes me wonder is if it's only positive to use a CLC, why wasn't it used in the original Aleph30 or Pearl?

When it's so nice, I'll add one also to the pearl of course, or is this just of academic value, because the fets contribute far more noise?

Interesting subject!

Thanks guys!

Any input appreciated! Have fun! Hannes
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Old 2nd February 2007, 11:01 AM   #6
jeapel is offline jeapel  Canada
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"thought there's an optimum inductor"

in my book maybe yes?

if you look CLC like C +LC

for LC fc=1/(6.28 x squareroot( LC) )

for power 50hz ripple=100hz
for power 60hz ripple=120hz

fc with factor 5 to 10 of ripple hz is good

optimum:

1-too low L = no effect
2-optimum is factor 5 to 10
3-too big L = difficult to find with low R and R= voltage drop and heat
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Old 2nd February 2007, 11:22 AM   #7
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Ok, I see what's the problem, you'll never get the inductors you would need.

So for a 3.9mH choke you would need just 26 Farads capacitance...

Or for 66000 uF only 1.55 Henry inductance...

So with what I could get, I'm just a factor 50 off what would be ideal.

I see. So better get a 6.8mH inductor then.

Have fun! Hannes

PS: but why are inductors so rarely used then? Too expensive or less efficient than adding capacitance for the same money?
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Old 2nd February 2007, 11:30 AM   #8
jeapel is offline jeapel  Canada
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?????????

if
L=3.9mH
C=66000uF

fc=9.92hz very good factor 10 and a little more

if my calculator hp is rigth or me :-)
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Old 2nd February 2007, 11:34 AM   #9
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Ah ok I misunderstood you!

You mean fc times 5-10 to get the 100/120Hz ripple would be ideal!

I see, thanks a lot for clarification!

Why 5-10 times?

Thanks a lot! Hannes
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Old 2nd February 2007, 12:27 PM   #10
jeapel is offline jeapel  Canada
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why factor 10

thumb law :-) for me factor 10 reduction of ripple is already very good

to give a good step down on speaker hum

factor 20 or 30 is better if and only if :

1-big inductor with big wire for low R

2-no magnetic saturation @ 10A (also thumb law)

3-maybe the money talk also :-)

in my aleph 3 the factor is 6,8 with good 25mv ac ripple

bye
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