Author Topic: Fire!!! (Tantalum capacitor - no trains were harmed in the making of this post)  (Read 565 times)

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craigolio1

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Found this one on Kemet site, page 5 talks about failire rates and influencing factors etc etc.
https://sh.kemet.com/Lists/FileStore/Derating%20Guidelings%20for%20Tantalum%202011%20(3).pdf
I will continue to use max applied voltage of 50% Of rated  for tantalum and 80% for poly tantalum caps too. And still do a burn in test on my 18v power drill battery before use in a model.

How long do do the burn in? Should it be called a “hopefully it doesn’t burn in”?

Steveruger45

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How long do do the burn in? Should it be called a “hopefully it doesn’t burn in”?

I do my burn in tests for an hour. 
Word of warning, tantalum caps can fail dramatically, i have seen this happen on my burn in tests hooked upto an 18v power tool battery.
Best to wear goggles when you hook up the last wire to the power supply and/or use long wires so you are far away from the caps when that last wire connection is made at the power supply.
Do the test on a concrete floor or piece of tile and away from anything explosive.

That said, i have never had a quality brand cap from digikey explode/fail.
I use only poly tantalum caps now with a rated voltage of either 20v or 25v.
My models are worth more to me than the cost difference on cap quality and lower voltage rating.
I removed all the cheap tantalum caps i initially Installed that I initially purchased on Ebay from a seller in China which were BTW rated at 25v.
« Last Edit: September 03, 2020, 09:50:58 AM by Steveruger45 »
Steve
Atascocita, Texas

jdcolombo

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The tantalum polymer cap that Rick B. linked to is an excellent choice.  It's the same physical size as the 16v one that I linked to, so there is absolutely no reason to use the lower voltage version.  Physically, it is a bit smaller than two "regular" tantalum chip caps mounted side-by-side, and with a depth of only 2mm you should be able to find room for a 4mm "stack" on a diesel chassis "shelf" that would give you 440uf of capacitance, which I've found eliminates 99.9% of sound dropouts in engines with relatively clean wheels on relatively clean track.

$3.50 each isn't cheap, but it's a lot cheaper than buying a new shell (if you could even get one) or blowing up a $90 sound decoder.

Right now I'm running all steam on my layout, and I replaced all my DIY keep alives in my tenders with TCS KA-1's or KA-3's, so this problem has taken care of itself with my steam fleet.  Now that my diesels are stored for a while (I haven't permanently converted to all steam; I'm just having some backdating fun for now), I'm thinking it might be a good time to update the cap installs with the ones Rick linked to.

John C.

reinhardtjh

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Right now I'm running all steam on my layout ...  Now that my diesels are stored for a while (I haven't permanently converted to all steam; I'm just having some backdating fun for now), I'm thinking it might be a good time to update the cap installs with the ones Rick linked to.
John C.

So that's why you needed those 5 Berks.  :D
John H. Reinhardt
PRRT&HS #8909
C&O HS #11530
N-Trak #7566

jdcolombo

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So that's why you needed those 5 Berks.  :D

Well, I didn't exactly NEED them . . . :)  But they did augment the fleet from 11 to 14 (I used two of them to retire the Bachmann versions I was never happy with; recycled the Bachmann smokebox cover to add a Mars light to the front of the LL version.  Too bad I can't get that as a separate part from Bachmann).   Current steam count is 14 Berks,  8 Mikes, two Connies and a lonely 10-wheeler sitting at an elevator to do switching duties . . . all with sound and TCS keep alives (yes, even the 10-wheeler, thanks to its oversize tender).

John C.

craigolio1

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Indeed when I burned up the two caps that I tested I was doing it on concrete and I wasn’t close enough to suffer any ill effects when it went. It was spectacular though. One developed a hole, flames shot out, and then it turned bright red, then white. Then it was just a simmering mass. Possibly a small black hole. The second one I didn’t see but it nearly completely disintegrated.

I’ve ordered some of both of the caps in the links. I like the two options for package sizes.

Thanks for the advice everyone.

Craig.
« Last Edit: September 03, 2020, 04:37:49 PM by craigolio1 »