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Old 23rd May 2011, 02:34 PM   #21
anilva is offline anilva  India
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Quote:
Originally Posted by AndrewT View Post
Improve the ventilation around the capacitors. You must do everything you can to keep them cool. Even adding extra C if necessary. Try replacing the first 22mF C with ten 2m2F Cs in parallel. Use the 22mF as an extra final C
Thanks.

Firstly the caps are rated to work upto 105 degrees C. Does that mean they will degrade over a period of time?

Secondly, does it help in terms of heat distribution, to move one 22mF from the last pair to the front and thus making them CCrCCrC instead of CrCCrCC?

Cheers.
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Old 23rd May 2011, 06:58 PM   #22
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Quote:
Originally Posted by anilva View Post
I have just completed making a PCB for my F5 PSU. The circuit I have used is an adaptation of NPs PSU schematic. Instead of CCRCC, I have used CRCCRCC.
What you have to watch for is the first C after the rectifier bridge. It will
see most of the ripple current, and it is likely that you will exceed its
ratings.

The ripple it will see will be a serious multiple of the actual draw due to the
lower power factor of such a system - it draws high current from the bridge
for short durations, and as a rule of thumb the internal dissipation of the
capacitor sees wattage which is proportional to the cycle time divided by
the charge time.

1.5 amps draw of the amp could look like 6 or more amps to the capacitor,
so you want to see that you have adequate ripple capacity on the initial
set of caps, likely achieved by paralleling.

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Old 23rd May 2011, 07:08 PM   #23
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40 degrees hot caps will last for years. 105 degrees hot caps will last a couple of months.
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Old 23rd May 2011, 07:24 PM   #24
anilva is offline anilva  India
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Quote:
Originally Posted by Nelson Pass View Post
What you have to watch for is the first C after the rectifier bridge. It will
see most of the ripple current, and it is likely that you will exceed its
ratings.

The ripple it will see will be a serious multiple of the actual draw due to the
lower power factor of such a system - it draws high current from the bridge
for short durations, and as a rule of thumb the internal dissipation of the
capacitor sees wattage which is proportional to the cycle time divided by
the charge time.

1.5 amps draw of the amp could look like 6 or more amps to the capacitor,
so you want to see that you have adequate ripple capacity on the initial
set of caps, likely achieved by paralleling.

Thanks Papa.

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Old 23rd May 2011, 07:38 PM   #25
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You're welcome. I wouldn't want you to find your caps all bloated up
after a couple months.

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Old 23rd May 2011, 08:42 PM   #26
anilva is offline anilva  India
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Quote:
Originally Posted by Nelson Pass View Post
You're welcome. I wouldn't want you to find your caps all bloated up
after a couple months.

Bloating may be tolerated, but if they explode when listening to nice music, that would be 'special sound effects' and then convincing wife to allow me continue the hobby without being a danger to the neighborhood. :-)
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