Tantalum bead as a timing capacitor?

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Original build of a sub-audio oscillator with a tant bead timing cap - frequency set up OK at first, then started tottering about all over the place.

It was a new unused part, but it had been in the parts drawer for a LONG time - I'd like to understand whether it was an age deteriorated component, or not suitable for the application.

Ended up with an MLCC capacitor - initial warm up drift, but doesn't wander far once its settled.

Thanks.
 

jpanhalt

Joined Jan 18, 2008
11,088
Interesting observation. My initial thought was aging, but apparently MLCC caps show that more than tantalums:
http://www.kemet.com/Lists/Technica.../2008-11 Update - Ceramic versus Tantalum.pdf

And in fact, tantalums are supposed to be more stable:
https://passive-components.eu/there-is-now-an-alternative-to-solid-tantalum-capacitors/

Although neither reference is on point for what you observed, the comment in the first link (page 3, #6) about volumetric efficiency caught my eye. That is, tantalums had 100:1 advantage early on (tantalums being smaller for the same capacitance). As of 2008, that had been reduced to 2:1. I haven't bothered checking more recently, nor have I checked relative pricing. But, I will certainly consider it the next time I order tantalums.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Interesting observation. My initial thought was aging, but apparently MLCC caps show that more than tantalums:
http://www.kemet.com/Lists/TechnicalArticles/Attachments/93/2008-11 Update - Ceramic versus Tantalum.pdf

And in fact, tantalums are supposed to be more stable:
https://passive-components.eu/there-is-now-an-alternative-to-solid-tantalum-capacitors/

Although neither reference is on point for what you observed, the comment in the first link (page 3, #6) about volumetric efficiency caught my eye. That is, tantalums had 100:1 advantage early on (tantalums being smaller for the same capacitance). As of 2008, that had been reduced to 2:1. I haven't bothered checking more recently, nor have I checked relative pricing. But, I will certainly consider it the next time I order tantalums.
Foil types wouldn't have raised the issue - but I want a very compact assembly.

Downloaded a load of documents last night - but its pretty dry reading...…………..
 

jpanhalt

Joined Jan 18, 2008
11,088
We don't know what capacitance you need, but I checked Digikey for 10 uF/16V caps. The smallest package for tantalums in SMD is an 805 package. Ceramic are available in 508, 603, and 805 packages. That surprises me, as I have not bothered to check recently.
 

AnalogKid

Joined Aug 1, 2013
9,189
One of the reasons the MIL used to love dry tants (as opposed to set slug) was their long-term life and stability, especially at high and low temps. Now days they're out of favor. Still I've not heard of your kind of problem before. Which ceramic dialectric did you end up using?

ak
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
We don't know what capacitance you need, but I checked Digikey for 10 uF/16V caps. The smallest package for tantalums in SMD is an 805 package. Ceramic are available in 508, 603, and 805 packages. That surprises me, as I have not bothered to check recently.
Started with a 10u/16v bead, but the pots were nearly end stopped - the MLCC is 22u.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
One of the reasons the MIL used to love dry tants (as opposed to set slug) was their long-term life and stability, especially at high and low temps. Now days they're out of favor. Still I've not heard of your kind of problem before. Which ceramic dialectric did you end up using?

ak
Not seeing many large tants these days - near as I can tell its mostly about bad PR around banana republics using child labour to chip it out of the rocks. The press I see hasn't informed me of any technical reason.
 

AnalogKid

Joined Aug 1, 2013
9,189
They are banned on submarines because of what they can put into the air when they burn. Over the years the list of prohibited substances on subs has grown.

ak
 

AnalogKid

Joined Aug 1, 2013
9,189
Presumably that would also apply to any aircraft with a pressurized cabin.
Nope. At least not in my experience, and we built stuff for all of the big boys. Toward the end of my run, all specs has a restricted materials list. But the sub folks were just pain different. Again in my experience, they led the move from hexavalent to trivalent chromium as a surface treatment of aluminum.

ak
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Nope. At least not in my experience, and we built stuff for all of the big boys. Toward the end of my run, all specs has a restricted materials list. But the sub folks were just pain different. Again in my experience, they led the move from hexavalent to trivalent chromium as a surface treatment of aluminum.

ak
Some of it is the EU RoHS regs reaching globally because every country wants the ability to trade with the EU. Except us - apparently...…..

high on the lists of Brexiter's whinging was Brussels telling us what to do in the form of EU regs. If we drop EU regs - every other country will block UK exports to avoid contaminating their inventory.
 

jpanhalt

Joined Jan 18, 2008
11,088
Some of it is the EU RoHS regs reaching globally because every country wants the ability to trade with the EU. Except us - apparently...…..
We will always trade with you. :)

Now, as for where the population in the world is concentrated, I don't think which chromium oxidation state is used in Alodine and similar treatments will make a big difference.

There is a lot of great stuff in Europe, including most of my genetic heritage, but to ignore India and Asia is a huge mistake IMHO. My son will be leaving in July for additional experience in Ahmedabad, India. Imagine a city of 5.6 million in the metropolis drawing from a population of 60 million.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
We will always trade with you. :)

CE compliant audits aren't cheap - guaranteeing parallel inventories don't contaminate each other is MASSIVELY more not cheap.

Now, as for where the population in the world is concentrated, I don't think which chromium oxidation state is used in Alodine and similar treatments will make a big difference.

One of the chromium compounds is banned under the RoHS directive - but I forget which one.


There is a lot of great stuff in Europe, including most of my genetic heritage, but to ignore India and Asia is a huge mistake IMHO. My son will be leaving in July for additional experience in Ahmedabad, India. Imagine a city of 5.6 million in the metropolis drawing from a population of 60 million.
We will always trade with you. :)

Now, as for where the population in the world is concentrated, I don't think which chromium oxidation state is used in Alodine and similar treatments will make a big difference.

There is a lot of great stuff in Europe, including most of my genetic heritage, but to ignore India and Asia is a huge mistake IMHO. My son will be leaving in July for additional experience in Ahmedabad, India. Imagine a city of 5.6 million in the metropolis drawing from a population of 60 million.

They'll all be lining up to flog us crap (and America will see how much they can screw us for crap) - what they won't do is contaminate their inventory with our non compliant crap. When we've got no balance of trade - you'll get very bored standing on your market stall...…...
 

jpanhalt

Joined Jan 18, 2008
11,088
Yes, definitely worth repeating. I hope I didn't upset you too much.

I agree on the "crap" part and have dealt with it all my professional life. But, that will change. The system in China will never be identical to ours, but it will not remain an oligarch slave-like state. At least, I hope not. India is a huge competitor today. The largest tractor manufacturer worldwide is no longer John Deere, it is Mahindra in India.

Regards, John
 

Thread Starter

ian field

Joined Oct 27, 2012
6,539
Yes, definitely worth repeating. I hope I didn't upset you too much.

I agree on the "crap" part and have dealt with it all my professional life. But, that will change. The system in China will never be identical to ours, but it will not remain an oligarch slave-like state. At least, I hope not. India is a huge competitor today. The largest tractor manufacturer worldwide is no longer John Deere, it is Mahindra in India.

Regards, John
Our Royal Enfield motorcycle plant ended up in India - and China ripped off one of the Landrover models.
 
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