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Old 02-27-2019, 12:16 PM   #31
gregc
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Originally Posted by Overkast View Post
... but extremely risky to bet on.
you need to understand what the tolerances are on the specs (10% ?)

my experience with electrolytic caps is that the simply pop. I don't know if the generate any heat that might damage surrounding components.

the tantalum created a bright flash and burned for several seconds which would definitely damages nearby components. Fortunately, it was an unpainted brass loco which wasn't damaged.

tantalum caps probably should not be used if a failure can cause damage
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Old 02-27-2019, 12:21 PM   #32
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you need to understand what the tolerances are on the specs (10% ?)

my experience with electrolytic caps is that the simply pop. I don't know if the generate any heat that might damage surrounding components.

the tantalum created a bright flash and burned for several seconds which would definitely damages nearby components. Fortunately, it was an unpainted brass loco which wasn't damaged.

tantalum caps probably should not be used if a failure can cause damage
The usual reason for failure of tantalum caps in this fashion is they were installed with reverse polarity. I've seen a number of instances where equipment was popping like firecrackers on the 4th of July, they were all reverse polarity situations. Without abuse, tantalum caps have a much better MTBF than electrolytic caps.
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Old 02-27-2019, 02:03 PM   #33
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Without abuse,

ahhh, magic words ...
you forgot to tell those other people, lol
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Old 03-01-2019, 06:49 AM   #34
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... they were all reverse polarity situations..
i did have a hard time determining the polarity and paid particular attention to it. But that sounds like a better explanation.

I'll have to try building one again using the tantalums i have.
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Old 03-01-2019, 09:42 AM   #35
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The little dipped ones sometimes are pretty hard to see what the polarity is. That's the type I had exploding all over in my video generators, the assembly house had assembled several hundred boards with these reversed in polarity! Some lasted for over a year before they popped. Since they were just bulk bypass caps, it didn't affect the operation of the video boards as a rule. However, we found it when several customers told us our video boxes were popping like firecrackers. I had a couple of techs running around Wall St. after hours swapping out all the caps for several months, what a giant PITA!

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Old 03-01-2019, 11:19 AM   #36
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the ones i have a surface mount and boxes. I guess I'm not sure whether the bar marks the positive or negative side

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Old 03-01-2019, 11:30 AM   #37
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The bar on these are the positive end. However, larger round electrolytic caps have the black band as negative, go figure.
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Old 03-01-2019, 11:37 AM   #38
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how do you know the mark marks the positive end? spec sheet? The positive is marked on the dipped tantalums, inconsistent with electrolytics
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Old 03-01-2019, 11:38 AM   #39
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SMD caps, the polarity indicator will be a bar at the end of the device that is the positive end for capacitors . Electolytics are usually marked on the negative end ...
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Old 03-01-2019, 03:27 PM   #40
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how do you know the mark marks the positive end? spec sheet? The positive is marked on the dipped tantalums, inconsistent with electrolytics
Because tantalum caps are marked that way. Yes, look at the spec sheet for your caps.
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