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Old 21st December 2009, 08:06 PM   #1
rubli is offline rubli  Mexico
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Default importance of phisical size ???

Hi

many discussions flows around the importance of size.. this time I am talking about electrolityc caps. I came across a leaked 470uF @ 35V. and found a replacement that is much much smaller. is there any difference in performance ? any info I am missing ? I am kind of doubtful in just using the smaller part. both are 105 degrees.

the TO220 transistor is just for size reference.

Thanx !!!
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Old 21st December 2009, 08:11 PM   #2
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Can you compare datasheets? I would expect peak ripple current to be different.
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Old 21st December 2009, 09:08 PM   #3
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the bigger cap will also have a lower ESR.
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Old 21st December 2009, 09:18 PM   #4
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The green "no-name" replacement cap will have inferior ESR and ripple current rating as compared to the larger cap. The large dark-blue cap (the bad one?) looks like a Panasonic HFQ series, good stuff at the time, but now fairly mediocre in terms of ratings. These have been superseded by the Panasonic FC series. Did the cap come out of a switching power supply?
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Old 21st December 2009, 09:19 PM   #5
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Quote:
Originally Posted by Iain McNeill View Post
the bigger cap will also have a lower ESR.
Is that a fact?
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Old 21st December 2009, 09:28 PM   #6
rubli is offline rubli  Mexico
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The original Cap is from a ROTEL cd unit, and is the first cap after the rectifiers. it smoothes the voltage before a 7812 Chip. (there is a mirror circuit for the Vminus.) I plan to change both caps. as said, this cap was leaking to the extent of blowing the AC fuse after 20 seconds.
regards
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Old 21st December 2009, 09:35 PM   #7
Ltralus is offline Ltralus  Denmark
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Quote:
Originally Posted by wrenchone View Post
The green "no-name" replacement cap will have inferior ESR and ripple current rating as compared to the larger cap. The large dark-blue cap (the bad one?) looks like a Panasonic HFQ series, good stuff at the time, but now fairly mediocre in terms of ratings. These have been superseded by the Panasonic FC series. Did the cap come out of a switching power supply?
Not necessarily, nothing is written in stone when it comes to caps. The "no name" cap just tells you that you haven't got the necessary information to make an informed decision. It could be ultra low ESR for all you know, it could be an order of magnitude lower than the larger cap taking advantage of ten years worth of advancement. Even if it doesn't it will have lower ESR than a leaked cap which could also be any number of others from panasonic's leaky line, that FC only superseded in specifications but not sonically. I just replaced "badcaps" in a monitor with modern and stable caps that are 1/2 to 1/4 the physical size of the originals, and will last 4 times longer than the expected lifespan that the original caps would have had they not been destined to an early death due to their unstable nature. It is also probably fair to say the larger cap will have higher ESL.
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