Author Topic: Tantalum capacitor anode designation  (Read 1869 times)

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160pennsy

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Tantalum capacitor anode designation
« on: March 21, 2016, 03:07:27 PM »
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I purchased some of the following 220uF 20v tantalum capacitors (along with some Fox/Wildcat speakers) from Digi-Key and they just arrived. They are for a Soundtraxx Economai steam decoder install into a Bachmann 2-8-0 and I'm having trouble identifying the anode lead on this particular capacitor. There is no visible marking on the case. The photo and spec sheet url's are enclosed and they have notes on anode lead but it's incredibly difficult to see any difference between the two leads (using Optivisor) ...can anyone assist?



http://www.digikey.com/product-detail/en/vishay-sprague/597D227X9020R2T/718-1633-6-ND/1973981

http://www.vishay.com/docs/40047/597d.pdf
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peteski

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Re: Tantalum capacitor anode designation
« Reply #1 on: March 21, 2016, 03:25:49 PM »
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That is funny Paul.  Did you notice the large nipples on one of the terminals?  That is the anode (+).  :)
To confirm, I looked at the PDF file and the dimensions drawing.  There you will see mention that "Tantalum wire
nib identifies anode (+) terminal".

But then again, one cannot be careful enough when dealing with tantalum caps!  Install them in backwards and they explode!

EDIT:  just to clarify the statement I made about you being funny, that was related to you saying that you couldn't tell the difference between the leads.  To me it was like night and day. But I know this is a surface mounted device which has no leads - only solder terminals on each end (where one end is plain and the other end has very visible nipples).  I suspect that you might have thought that those 2 nipples were the cap's terminals. But since then are both electrically connected by the metallic coating, they bot are the same terminal (positive).
« Last Edit: March 21, 2016, 03:45:25 PM by peteski »
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C855B

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Re: Tantalum capacitor anode designation
« Reply #2 on: March 21, 2016, 03:27:09 PM »
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I see the confusion. Pete got to it before I could hit "Post" - the "wires" are just orientation nibs, and BOTH identify the (+) side. Think "surface mount" - you solder to the ends of the case. So the plain end without the nibs is (-). Other models of this capacitor design have only one nib, so lucky you.
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peteski

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Re: Tantalum capacitor anode designation
« Reply #3 on: March 21, 2016, 03:39:29 PM »
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I suspect the dual nibs on the positive terminal are due to the internal construction of the capacitor. It is a large-capacity unit which is internally made up from 2 parallel connected capacitors which are then encapsulated in the orange epoxy shell.  All the tantalum caps HI have dealt with have a wire coming out on the positive side (that is just how they are made). But in the caps with molded cases that wire is usually not externally visible.

In my experience with tantalum caps, the unusual looking electrode (or marked electrode) are anodes.  Which is the opposite of electrolytic caps where the marked electrode is cathode. 
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160pennsy

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Re: Tantalum capacitor anode designation
« Reply #4 on: March 21, 2016, 04:46:27 PM »
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I see the confusion. Pete got to it before I could hit "Post" - the "wires" are just orientation nibs, and BOTH identify the (+) side. Think "surface mount" - you solder to the ends of the case. So the plain end without the nibs is (-). Other models of this capacitor design have only one nib, so lucky you.

Thank you Mike & Pete. Hopefully when I finish the install & power up there will be no explosions! Now I can finish placing my order at MBK for a Bachmann DCC ready WM tender. The original tender that came with my 2-8-0 is an older vintage with plastic floor & sides all as one piece and a removable top w/metal weight. The newer DCC ready tenders have metal floors w/ lift off shells which make it much easier to solder wires to the tender pickup strips.
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peteski

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Re: Tantalum capacitor anode designation
« Reply #5 on: March 21, 2016, 05:59:31 PM »
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Paul,
those high-capacitance 20V tantalum caps are very pricey!  Are you really saving that much space using those rather than using 100 or 150 uF 20V caps wired in parallel? Those caps are much less expensive.  I usually gang 4 or 5 of the 100 or 150 uF caps in my models.
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160pennsy

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Re: Tantalum capacitor anode designation
« Reply #6 on: March 22, 2016, 09:50:11 AM »
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Paul,
those high-capacitance 20V tantalum caps are very pricey!  Are you really saving that much space using those rather than using 100 or 150 uF 20V caps wired in parallel? Those caps are much less expensive.  I usually gang 4 or 5 of the 100 or 150 uF caps in my models.

Compared to the 220uF 25V electrolytic "can" capacitor that came with the Economai decoder it's about 1/3 of the size (I'll try to post a photo later). When I first started this project I was still using the old tender (with plastic floor & sides) & wanted to retain as much of the metal weight as possible for good electrical pickup. There was not a lot of room left inside there once the decoder & speaker placement was worked out. After finding the inexpensive bare Fox Wildcat speakers on DigiKey I needed to order the capacitors & some resistors to make the shipping worthwhile. Those capacitors were the first or second ones I found that had the right electrical specs, fit my size requirements and avoided any messing around with wiring two together to get the right value. Didn't fully see the price till I was finishing my order but now I'll have a few extra for my next project along with some speakers.
Paul Ohegyi
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peteski

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Re: Tantalum capacitor anode designation
« Reply #7 on: March 22, 2016, 04:07:10 PM »
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I never questioned the fact that the capacitance density (is that a real definition?) of tantalum caps is much greater than aluminum electrolytics.  Plus their shape is also conducive to fitting more capacitance in tighter area.

But why spend $11 per cap if using two $2 caps will give you the same capacitance in the same (or slightly greater) volume.  Hey, but since you now have those pricey caps, you're good to go.
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