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I got some capacitors about two years ago now, which I foolishly removed from their bag, and I quickly forgot their markings. I can't even figure out which kind of capacitor it is. Tantalum seems the most similar, but the markings are wrong for a tantalum cap. Could you please help me identify this?

Help me identify this!

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  • \$\begingroup\$ Note that on many Tantalum disasters-waiting-to-happen there is what appears to be a "-" marked - this is next to the positive terminals. So 'turning it around' may be correct polarity. Test: Charge a largish electrolytic (say 1000 uF) to the rated voltage of this cap and apply it to samples of this cap in either polarity sequentially. Use requisite eye (at least) protection. The polarity that self destructs most often is the wrong one. \$\endgroup\$ – Russell McMahon Feb 10 '14 at 6:43
  • \$\begingroup\$ @RussellMcMahon The data sheet for Kemet's Polymer-Tantalum caps says (in part) : "The KOCAP also exhibits a benign failure mode which eliminates the ignition failures that can occur in standard MnO2 tantalum types.". Strangely, I can find nothing about the "ignition failure" feature in their other data sheets. kemet.com/kemet/web/homepage/kechome.nsf/file/T520%20Series/… \$\endgroup\$ – Spehro Pefhany Feb 10 '14 at 11:06
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That is odd.

The stylized K is a trademark of Kemet, who makes both ceramic and tantalum caps.

The polarization marking would indicate tantalum, but the capacitance (if it's only 10,000pF) is rather small for a 25V rated tantalum cap.

My best guess is that this is a 10uF +/- 10% (K tolerance) 25V solid tantalum capacitor.

Edit:

Turns out it was a pretty good guess. Here's the data sheet (towards the back). It's a MIL-spec solid tantalum cap.

enter image description here

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  • \$\begingroup\$ They were in their original packaging at a HAMfest; the stickers were freshly printed. When i've used it in circuits, it seems about equivalent to a 10uf capacitor, but if i flip it around, it seems like it has a little more capacitance... I really don't know what to make of it. I think I remember the seller saying they were good for, well, radio equipment or something (may not help much; we were at a HAMfest after all). I don't think they are from '88. \$\endgroup\$ – Wyatt8740 Feb 10 '14 at 1:38
  • \$\begingroup\$ If it's a tantalum cap, flipping it around won't do it much good. Vishay says: Q. HOW LONG CAN YOU OPERATE VISHAY SOLID TANTALUMS WITH THE APPLIED REVERSE VOLTAGE BIAS? A. Tantalum capacitors are capable of withstanding peak voltages in the reverse direction equal to 10 % of the DC rating at + 25 °C and 5 % of the DC rating at + 85 °C. vishay.com/docs/40110/faq.pdf \$\endgroup\$ – Spehro Pefhany Feb 10 '14 at 1:45
  • \$\begingroup\$ I have found a patent filed by kemet in 2007 that looks like it might be relevant. At least physically. google.com/patents/US8057883 \$\endgroup\$ – Wyatt8740 Feb 10 '14 at 1:51
  • \$\begingroup\$ I think I found it! THANK YOU GOOGLE IMAGES! I think it's the t340 or t370 series. kemet.com/kemet/web/homepage/kechome.nsf/weben/… \$\endgroup\$ – Wyatt8740 Feb 10 '14 at 2:11
  • \$\begingroup\$ See my edited answer above \$\endgroup\$ – Spehro Pefhany Feb 10 '14 at 2:53
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Alright, it took a while, but with google images I found it, I think.

I think it's the Kemet t340 or t370 series - series datasheet here


RM: The following was retained for information

(1) Update: I expect the material below the above line will get deleted in due course, but is placed here for now for information. The sentence below is false. The new link works, BUT only if you click on "link" and not if you click on the 'more obvious' url shown.

(2) False: The following advance link creation attempt failed, as did the simpler original version - presumably due to the $. The above uses bit.ly. It may even work, or not.

link (url: http://www.kemet.com/kemet/web/homepage/kechome.nsf/weben/547892805FE03DD7CA2570A600107AD6/$file/F3100.pdf )

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  • 1
    \$\begingroup\$ I tweaked your answer since the link wasn't parsed properly by stack-exchange. Apparently they think you can't have "$" in a url. \$\endgroup\$ – Connor Wolf Feb 10 '14 at 6:41
  • \$\begingroup\$ I added a bit.ly jump (which worked when I tested it) as the corrected link link works but is easily misused. \$\endgroup\$ – Russell McMahon Feb 10 '14 at 16:25
  • \$\begingroup\$ thanks :) I appreciate it. (I think i ended up frying that cap while experimenting with it, but I have 6 more, so everything is good!) \$\endgroup\$ – Wyatt8740 Feb 18 '14 at 7:39
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This is an "ancilliary answer" [tm]

You say:

but if i flip it around, it seems like it has a little more capacitance...

Low cost milspec tantalum capacitors from a Hamfest are well worth using if they meet a significant need in an amateur situation where failure (and just possibly conflagration) is acceptable.

Otherwise, solid tantalum capacitors are disasters waiting to happen.
Rigorous design and implementation that guarantees that their requirements are met can produce highly reliable designs. If your real world situations are always guaranteed to not have out of spec exceptions then tantalum caps may work well for you, too.
Good luck with that.


Spehro notes:

  • The data sheet for Kemet's Polymer-Tantalum caps says (in part) : "The KOCAP also exhibits a benign failure mode which eliminates the ignition failures that can occur in standard MnO2 tantalum types.".

    Strangely, I can find nothing about the "ignition failure" feature in their other data sheets. these particular tantalum caps

Solid Tantalum electrolytic capacitors have traditionally had a failure mode which makes their use questionable in high energy circuits that cannot be or have not been rigorously designed to eliminate any prospect of the applied voltage exceeding the rated voltage by more than a small percentage.

Tantalum caps are typically made by sintering tantalum granules together to form a continuous whole with an immense surface area per volume and then forming a thin dielectric layer over the outer surface by a chemical process. Here "thin" takes on a new meaning - the layer is thick enough to avoid breakdown at rated voltage - and thin enough that it will be punched through by voltages not vastly in excess of rated voltage. For an eg 10 V rated cap, operation with say 15V spikes applied can be right up there with playing Russian Roulette. Unlike Al wet electrolytic caps which tend to self heal when the oxide layer is punctured, tantalum tends not to heal. Small amounts of energy may lead to localised damage and removal of the conduction path. Where the circuit providing energy to the cap is able to provide substantial energy the cap is able to offer a correspondingly resistant low resistance short and a battle begins. This can lead stp smell,smoke, flame, noise and explosion. I've seen all these happen sequentially in a single failure. First there was a puzzling bad smell for perhaps 30 seconds. Then a loud shrieking noise, then a jet of flame for perhaps 5 seconds with gratifying wooshing sound and then an impressive explosion. Not all failures are so sensorily satisfying.

Where the complete absence of overvoltage high energy spikes could not be guaranteed, which would be the case in many if not most power supply circuits, use of tantalum solid electrolytic caps would be a good source of service (or dire department) calls. Based on Spehro's reference, Kemet may have removed the more exciting aspects of such failures. They still warn against minimal overvoltages.

Some real world failures:

enter image description here

Wikipedia - tantalum capacitors

  • Most tantalum capacitors are polarized devices, with distinctly marked positive and negative terminals. When subjected to reversed polarity (even briefly), the capacitor depolarizes and the dielectric oxide layer breaks down, which can cause it to fail even when later operated with correct polarity. If the failure is a short circuit (the most common occurrence), and current is not limited to a safe value, catastrophic thermal runaway may occur (see below).

Kemet - application notes for tantalum capacitors

  • Read section 15., page 79 and walk away with hands in sight.

AVX - voltage derating rules for solid tantalum and niobium capacitors

  • For many years, whenever people have asked tantalum capacitor manufacturers for general recommendations on using their product, the consensus was “a minimum of 50% voltage derating should be applied”. This rule of thumb has since become the most prevalent design guideline for tantalum technology. This paper revisits this statement and explains, given an understanding of the application, why this is not necessarily the case.

    With the recent introduction of niobium and niobium oxide capacitor technologies, the derating discussion has been extended to these capacitor families also.

Vishay - solid tantalum capacitor FAQ

  • . WHAT IS THE DIFFERENCE BETWEEN A FUSED (VISHAY SPRAGUE 893D) AND STANDARD, NON-FUSED (VISHAY SPRAGUE 293D AND 593D) TANTALUM CAPACITOR?

    A. The 893D series was designed to operate in high-current applications (> 10 A) and employs an “electronic” fusing mechanism. ... The 893D fuse will not “open” below 2 A because the I2R is below the energy required to activate the fuse. Between 2 and 3 A, the fuse will eventually activate, but some capacitor and circuit board “charring” may occur. In summary, 893D capacitors are ideal for high-current circuits where capacitor “failure” can cause system failure.

    Type 893D capacitors will prevent capacitor or circuit board “charring” and usually prevent any circuit interruption that can be associated with capacitor failure. A “shorted” capacitor across the power source can cause current and/or voltage transients that can trigger system shutdown. The 893D fuse activation time is sufficiently fast in most instances to eliminate excessive current drain or voltage swings.

Capacitor guide - tantalum capacitors

  • ... The downside to using tantalum capacitors is their unfavorable failure mode which may lead to thermal runaway, fires and small explosions, but this can be prevented through the use of external failsafe devices such as current limiters or thermal fuses.

What a cap-astrophe

  • I was working at a manufacturer that was experiencing unexplained tantalum-capacitor failure. It wasn't that the capacitors were just failing, but the failure was catastrophic and was rendering PCBs (printed-circuit boards) unfixable. There seemed to be no explanation. We found no misapplication issues for this small, dedicated microcomputer PCB. Worse yet, the supplier blamed us.

    I did some Internet research on tantalum-capacitor failures and found that the tantalum capacitors' pellets contain minor defects that must be cleared during manufacturing. In this process, the voltage is increased gradually through a resistor to the rated voltage plus a guardband. The series resistor prevents uncontrolled thermal runaway from destroying the pellet. I also learned that soldering PCBs at high temperatures during manufacturing causes stresses that may cause microfractures inside the pellet. These microfractures may in turn lead to failure in low-impedance applications. The microfractures also reduce the device's voltage rating so that failure analysis will indicate classic overvoltage failure. ...

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  • \$\begingroup\$ My capacitor is being used to prevent a surge of power to the reset line when my NES starts up. The NES is modified with some shift registers to reset when I hold down A+B+Start+Select. THis is hardly a life-or-death situation. 5 volts DC power, reglated by a homemade switching voltage regulator, coming from an AT power supply. I will remember this if I decide to build something more productive :) (+1) \$\endgroup\$ – Wyatt8740 Feb 18 '14 at 7:41

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