Search google for ESR test,  There is a simple test you can perform.  All you need is a 100 & 5 ohm resistor, 100KHZ generator and a scope.  There are big differences in capacitors.  Everyone should build or own some sort of ESR tester.  Lot of info out there.  sencore.com has some simple tech tips to start understnding capacitors.

Read the spec sheet!

Bear in mind that purity of capacitance is a different measure of quality than physical construction - some very good capacitors in terms of low parasitics are a nightmare in assembly.
 

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If we learn from our mistakes I'm getting a great education!

You have to define what you mean by "quality".  Voltage, capacity, ESR, temperature, temperature coefficient, tolerance, life expectancy, , , , , , Taste?

There is no passive component with more aspects to be considered by a user than a capacitor.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

I hesitate to correct you Smoked. But, wouldn't "There is no component with more aspects to be considered by a user than a capacitor" be better?

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Could be..  But if I exclude "passive" then you open things to active, hence integrated circuits, hence micros.  Some I work with have three hundred pages of spec sheets.   I suspect you could argue that there are more aspects in that case than even the hard-to-pin-down capacitors.

That was my thinking Skogs..

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

I understand that Smoked. But then again, I could (if I wanted to) argue that those are not details that you have to consider in detail when you select a micro-processor. Or do you really evaluate every single instruction when you select one. I don't. I look for things like foot-print, supply voltage, speed, sometimes architecture and peripherals and sometimes temperature range.

So, I (and I really hope that you get my tounge-in-cheek) maintain that there are many more dimensions in the decision space whan it comes to capacitors than any other component.

As I said, I could have argued that way. But I didn't really.

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Well ... If you are comparing all caps verses all micros I would argue that the micros far "out complex" caps!  List every single capacitor parameter and I argue the micro question would be many times more daunting.  

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

It is an entertaining conversation we have here, Smoked. And even somewhat interesting. Have you really, I mean really, considered all capacitor types and all parameters?

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Heck no!  But all I suggest is you write down every possible parameter.   I would guess what, about 25?   All micros?  I would guess about 250 different aspects.

Capacitors are stuck with only 2 wires coming out.  A huge handicap in the battle of complexity.  

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

Hmm..

Just you wait!

Sorry, haven't got the time right now.

Will surely be back. Be prepared!

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

OK. It may be as you say. I admit it unwillingly.

But. Any computer guy can probably select a micro - can he select a capacitor?

Why is that so?

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Quote (Skogsgurra):

Any computer guy can probably select a micro - can he select a capacitor?

Why is that so?

Probably because more processor specs are taught in school than cap specs.  Caps are considered plug-n-play devices in most schools, and even working voltages are typically ignored.  Since most micro circuits work at 5V and below, almost every cap you pull off of the shelf is going to work.  Speeds are rarely beyond a few 10's of kHz (external to the processor), so again, there's not much need to worry about things like ESR or package inductance... those are best left to experience gained on the job (or so they feel).
When I was teaching some analog comm labs at Purdue, I was careful about not leaving out those kinds of details.  While I may not have covered everything, I tried to stress that there are always a myriad of specs one might need to look at that aren't necessarily obvious to the average engineer.  As it is, I still need to pull up Google and refresh my memory on the different cap types any time I start work in a "field" I haven't worked in for a while (such as audio, video, RF, etc.).

Dan - Owner
http://www.Hi-TecDesigns.com

Hey! Smoked!

"there are always a myriad of specs"

I like that. That's a lot more than your measly 250!

(A myriad is 10 000)

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Hahah!

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

Friends again?

I had a real killer ready for you if you had even thought about using that leg argument. Wish you had...

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Varying point of view/agreement should not be the basis of continued friendship!

Friends always man.

Legs?? = Leads??  Out with it! Lets hear it.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

Well..

Which one is the more complex organism? A human (two legs) or a centipede?

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

A capacitor is 1 circuit element, while a microprocessor is millions of circuit elements.  That is why a micro is more complex than a capacitor.

Chuckle.  You got me there Skogs!

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

My boss likes his capacitors the way he likes his suits.....Cheap and made out of polyester.

If the capacitance value is right and have chosen the lowest ESR, you have pretty much answered the looks and sounds like a duck question.  Given that it is a black box choice and the poor framing of the question.  

Not to mention, the active participation.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

This thread reminds me of the 10th item in this list.

http://www.engineeringhumor.com/Theorems01.htm

Hi all,

Agreed that the caps must be ESR tested if they are intended for apps at frequencies far from DC.
Honestly, for most applications (<1MHz, ambient temperature, etc.), I used X7R type ceramic chip caps, mainly because those are easier to find on Digikey or Mouser. Yes, it is not a very technical way to choose parts.

For tough environments like field devices, I use NPO type caps, that offer less capacitance drift over time/temperature.

For higher frequency applications, like PS filters, switching stages or analog, I choose tantalum or those marked by the manufcturer as 'Low ESR'. They are more costly , but save lots of problems on field.

Regards,
Gonzalo