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What type of capacitor is this...

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211

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I have a board that has a few of these 'type' capacitors on them. Looks like a bean.

Can someone identify the type of cap this is and why one like this would be used as opposed to a typical 'can' type capacitor?
 

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RCinFLA

Well-Known Member
Tantalum electrolytic 100 uF, 6 vdc

Tantalum use mixed 3 digit numbering convention. 476 means 47 uF. 100 means 100 uF.
 
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crutschow

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They build them with an epoxy coating since they are typically cheaper to construct then the "can" type. The inexpensive "can" types are also more typically Al electrolytics, not tantalum.
 

211

Member
Tantalum electrolytic 100 uF, 6 vdc

Tantalum use mixed 3 digit numbering convention. 476 means 47 uF. 100 means 100 uF.

Okay so that 6 printed underneath is the voltage not the multiplier?

They build them with an epoxy coating since they are typically cheaper to construct then the "can" type. The inexpensive "can" types are also more typically Al electrolytics, not tantalum.

So other than cost is there any performance benefit or any special characteristics with tantalum?

Thanks for the info's
 
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crutschow

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Tantalum electrolytics generally have better performance than Al electrolytics. They are smaller, have a better tolerance, lower leakage, and lower impedance (ESR).
 

RCinFLA

Well-Known Member
The primary attibute of tantalum is they can make them down to 2 wvdc breakdown voltage allowing a lot of capacitance in a small package. An alum oxide you won't find much below 10 wvdc, so for low voltage applications like battery operated portable devices they will be larger.

Tantalums have a bit higher Rs then alum oxide at low frequency but the Rs stays constant to a higher frequency compared to alum oxide electrolytics.

If it fits, you can most of the time substitute an alum oxide electrolytic. Some rare cases, the Rs of tantalum is used for a stability pole on output of a voltage regulator, but it is a rare case that it makes a difference.

Tantalum is a rare commodity so they are more expensive then aluminum electrolytics.
 
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audioguru

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I haven't used a tantalum capacitor for 30 years since most of them blew up. In the past 30 years I have never seen one in the many products that I looked in.
 

cachehiker

New Member
I haven't used a tantalum capacitor for 30 years since most of them blew up.

I remember them being quite fragile when subjected to adverse conditions as well.

We had a firm specify some big 16V tantalums for output decoupling on a 15V series pass regulator. Problem was the tolerance of the zener diode had the regulators varying from just under 15V to almost 17V. The capacitors had a very high failure rate at the higher end of that tolerance. The vendor was also later found to have a bad habit of inserting them backwards, having the regulator fail testing, and then reworking the boards by just reversing (instead of replacing) the cap. Those didn't last long either and often failed catastrophically. I remember one in particular starting to smoke, popping its top, shooting into the kraft paper fiberglass insulation above our heads, and sitting there smoldering for a while.

There are other stories but I personally have never had a tantalum fail when its application has stayed securely within its ratings.

And then there was that big, brute force Chicago Laser supply that kept eating some coffee can sized electrolytics... Good God what an awful smell.
 

audioguru

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I usually used a 16V or 25V tantalum capacitor across a regulated 5V supply. Most of them blew up.
The 5V TTL ICs never blew up so I don't think there were voltage spikes on the 5V.
The tantalum capacitors were usually made (in the late 70ies) by ITT.
 

cachehiker

New Member
I didn't start working in electronics until the late 80's when I was the only applicant for a particular position who was capable of identifying resistors, capacitors, op-amps, etc. on a schematic that was pushed across the desk at me. :D Maybe I've just been using more up to date and reliable components.

One of my two "mentors" had a thing about anything old and electrolytic and said something like "You wouldn't rely on a 20 year old battery, would you?" I'm not completely nutty about discarding old tantalum or aluminum electrolytics but I know their tendency to degrade when left without a voltage applied for long periods in storage. Maybe it's that I've never built any circuits using old (>10-20 years) capacitors.

In any case, I still employ his "trick" when stuck with an old electrolytic and unwilling to buy another bag of parts. He insisted on charging them up to their rated voltage through a big resistor (like 2.2MΩ-10MΩ), leaving them connected to the power supply for a day, and then testing them before using them. I don't know if it really does any good but I haven't had any fail in their application. I haven't had any test bad either though.
 

Dean Huster

Well-Known Member
Tektronix used tantalums by the millions in their many varied products and I've only had to replace one while working for them as a service bench tech. If you design the circuit properly, and use the right voltage ratings, tantalums are just fine. Another older marking type used the standard color code.
 
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