| Page 1 of 2 | 1 | 2 |
|
|
Tantalum caps.
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr |
Henry Kolesnik wrote:
Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr They can have very good characteristics (small size, low esr, high parallel resistance and good capacitance stability) but have some strange failure modes if they are misapplied. Digikey sells a great variety of them. I can seldom justify their cost in production designs, but use them quite often in one offs. -- John Popelish |
In article , Henry Kolesnik
writes Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr twere always regarded as more reliable than aluminum; however there is a failure mechanism associated with the source resistance and how close the operating voltage is to the maximum specified. Modern aluminum can have very low esr and an adequate alternative to tantalum. -- ddwyer |
John Popelish wrote:
Henry Kolesnik wrote: Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr They can have very good characteristics (small size, low esr, high parallel resistance and good capacitance stability) but have some strange failure modes if they are misapplied. Digikey sells a great variety of them. I can seldom justify their cost in production designs, but use them quite often in one offs. So in a production design, what would you use to get the equivalent performance? An aluminum electrolytic in parallel with a ceramic? -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ F o d d e r f o r s t u p i d n o t e n o u g h i n c l u d e d t e x t m s g |
On Wed, 21 Jan 2004 17:26:14 -0600, "Henry Kolesnik"
wrote: Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr We often use surface-mount tantalums on high-density, high-cost boards. They are very reliable (don't dry out like aluminums) if used carefully, but high peak currents can ignite them, so they are generally a bad idea for bypassing power rails. Polymer aluminums (don't dry out) or polymer tantalums (don't explode) seem like a good idea, but I haven't tried them yet. I think multilayer ceramics are pushing 100 uF these days. John |
"Watson A.Name \"Watt Sun - the Dark Remover\"" wrote:
John Popelish wrote: (snip) I can seldom justify their cost in production designs, but use them quite often in one offs. So in a production design, what would you use to get the equivalent performance? An aluminum electrolytic in parallel with a ceramic? A production design usually pays for the engineering necessary to reduce the need for premium quality components. Your solution is often a cheaper alternative to a premium quality tantalum. -- John Popelish |
I have a Racal 9301A where a tantalum must have caught on fire because all
that was left was 2 leads, some crisp blackish ash and a little hardened crust on the pcb where it burned. There's probaby 10 other tants on the board and one or more are shorted but still intact and I'm trying to find the bads one/ones with least effort without a schematic. The other unit is a Wavetek 188-S1257 where a tantalum had a dead short but was intact. I repalced it with an electrolytic. The cap is on a 15 volt rail where I think it shorted and took out the regulator. Ireplace the regulator with what I assumed was a good one out of a new box but it was bad and it put 23 volts on the rail that had a 20 volt rating but no more failed. Sometime I have good luck. 73 hank wd5jfr "John Larkin" wrote in message ... On Wed, 21 Jan 2004 17:26:14 -0600, "Henry Kolesnik" wrote: Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr We often use surface-mount tantalums on high-density, high-cost boards. They are very reliable (don't dry out like aluminums) if used carefully, but high peak currents can ignite them, so they are generally a bad idea for bypassing power rails. Polymer aluminums (don't dry out) or polymer tantalums (don't explode) seem like a good idea, but I haven't tried them yet. I think multilayer ceramics are pushing 100 uF these days. John |
Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a Consumer electronics are costed down to the lowest possible level. If they can use something cheaper, they WILL use something cheaper. A TV set or VCR has had people go over the design hundreds of times with BOMs and catalogs, checking to see if they can shave a penny here or a penny there. Computer equipment is a good source for tantalums - motherboards, hard drive PCBAs, etc. Of course, it will be surface-mount :) |
In article , "Henry Kolesnik"
writes: Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. Tantalum capacitors became a component item about 45 (or so) years ago and originally favored in spacecraft and aircraft because they could contain lots of electrostatic storage in a small space with ligher weight. That was when PCBs were relatively new, quite new in spacecraft electronics. It hasn't been until the last decade or so that the cost of tantalum capacitors has approached the level of improved electrolytic capacitors of the same value. Tantalums are still relatively expensive but they are good for SMT due to their smaller size; its a trade-off between cost and overall system size in that case. Inherent problems in tanatalum capacitors have been improved since their initial debut as a component but so have electrolytic capacitors and their manufacturing methods. One can purchase FARAD-value low-voltage electrolytics now where once it was not possible unless one had a room to put them in. Len Anderson retired (from regular hours) electronic engineer person |
I wouldn't assume that just because your test equipment comes to you broken
is a result of tantalum caps -- perhaps your sample is skewed by buying at hamfests instead of burgling active technology companies? Maybe if you only acquired your home entertainment equipment from dumpsters you'd conclude that aluminum electrolytics are bad? I recently escaped from a company that does aero (but not space) systems. They get mounted on aircraft and are expected to survive being shipped in an unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum electrolytic will dry out, but a tantalum will be fine. There are even wet-slug tantalums for high-altitude applications that will not dry out at these altitudes. The problems with tantalum are their fragility (we've had exploding caps on our boards, with one manufacturer's part being fine and another being horrid), cost, and the relative scarcity of tantalum. Does anyone remember the Great Tantalum Shortage of a couple of years ago? One of the big tantalum supplying regions is central Africa, and a combination of wars reducing supply and increased demand led to some supply problems for a while -- I remember that at least one of the manufacturers even came out with a Niobium cap as a substitute. "Henry Kolesnik" wrote in message ... Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr |
Hi all,
tantalum caps seem to be too expensive for consumer-grade equipment. They contain pricey material - silver and, of course, tantalum, so making them cheaper is impossible. AFAIK they are widely used in military-grade equipment, where the price is not an issue. Their main advantages are a longer life (they do not dry out nor leak) and a bigger temperature range (frost resistance). About using cheap parts in consumer electronics: At least 80 percent of failures of certain types of TV sets were caused by dried-out aluminum caps. The good practice when repairing these sets was: first check all electrolyte caps by adding a good one in parralel. It was successful very often. BR from Ivan |
John Larkin wrote:
I think multilayer ceramics are pushing 100 uF these days. Yes, but alas, only with zero volts across them. Capacitance drops precipitously with DC bias. For a cap with Y5V dielectric, at half the rated DC voltage, there's only 10% of the initial capacitance left. Most manufacturers don't tell you. |
"Jeroen" wrote in message ... John Larkin wrote: I think multilayer ceramics are pushing 100 uF these days. Yes, but alas, only with zero volts across them. Capacitance drops precipitously with DC bias. For a cap with Y5V dielectric, at half the rated DC voltage, there's only 10% of the initial capacitance left. Most manufacturers don't tell you. I didn't think it was quite as bad as that. Also very temperature dependent. These type of ceramics are also pyroelectric as well as being piezoelectric! |
On Thu, 22 Jan 2004 05:05:22 -0800, the renowned Bill Turner
wrote: On 21 Jan 2004 19:09:37 -0800, (Lewin A.R.W. Edwards) wrote: Consumer electronics are costed down to the lowest possible level. If they can use something cheaper, they WILL use something cheaper. A TV set or VCR has had people go over the design hundreds of times with BOMs and catalogs, checking to see if they can shave a penny here or a penny there. _________________________________________________ ________ Well, maybe. Any manufacturer who has been nailed with thousands of dollars in warranty costs caused by saving a penny might disagree with your statement. I've seen it happen. Caused by bad engineering (or purchasing), I would say. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
On Thu, 22 Jan 2004 08:54:58 +0100, Jeroen
wrote: John Larkin wrote: I think multilayer ceramics are pushing 100 uF these days. Yes, but alas, only with zero volts across them. Capacitance drops precipitously with DC bias. For a cap with Y5V dielectric, at half the rated DC voltage, there's only 10% of the initial capacitance left. Most manufacturers don't tell you. Which opens up the possibility of using them as parametric amplifiers or modulators. I have a paper somewhere that uses the nonlinearity of ceramic caps to make a nonlinear transmission line - a shock line - that sharpens the rising edge speed of kilovolt pulses. John |
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
wrote: I wouldn't assume that just because your test equipment comes to you broken is a result of tantalum caps -- perhaps your sample is skewed by buying at hamfests instead of burgling active technology companies? Maybe if you only acquired your home entertainment equipment from dumpsters you'd conclude that aluminum electrolytics are bad? I recently escaped from a company that does aero (but not space) systems. They get mounted on aircraft and are expected to survive being shipped in an unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum electrolytic will dry out, but a tantalum will be fine. There are even wet-slug tantalums for high-altitude applications that will not dry out at these altitudes. Wet-slug tants are expensive (do they still have silver cases?) but don't blow up like the dry ones. The dry slugs coat the sintered tantalum (fuel) with MnO2 (oxidizer). The problems with tantalum are their fragility (we've had exploding caps on our boards, with one manufacturer's part being fine and another being horrid), cost, and the relative scarcity of tantalum. This is really erratic. One spool of tants will be bombs, another can't be made to fail by deliberate abuse. John |
"John Larkin" wrote in message ... On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott" wrote: snip Wet-slug tants are expensive (do they still have silver cases?) but don't blow up like the dry ones. The dry slugs coat the sintered tantalum (fuel) with MnO2 (oxidizer). Boy are they ever. I have some surplus ones, but they have cases that are more of a silver-gray than that nice yellowish-white look you get from silver-plated connectors. These are special parts, but if you want a generally high-performance cap in a (relatively) small package they're hard to beat. I worked for a while on a project to make a power-wire networking device. During testing I accidentally dragged a scope ground across a circuit that was referenced to the 115V power line, thereby exceeding the tantalum cap's voltage rating -- er -- "slightly". Little pieces of flaming capacitors bounced around the lab. After that all of my digital logic (3.3V and lower) coworkers _never_ messed with my bench. The problems with tantalum are their fragility (we've had exploding caps on our boards, with one manufacturer's part being fine and another being horrid), cost, and the relative scarcity of tantalum. This is really erratic. One spool of tants will be bombs, another can't be made to fail by deliberate abuse. Interesting. I'll have to remember that. Thanks. In any case when designing with _any_ electrolytic capacitor it's best to use specify a cap for 20-50% higher voltage than what you think it's ever going to see, particularly because many voltage regulators overshoot on power up and the output cap sees more voltage than you think. John |
"John Larkin" wrote in message ... On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott" wrote: I wouldn't assume that just because your test equipment comes to you broken is a result of tantalum caps -- perhaps your sample is skewed by buying at hamfests instead of burgling active technology companies? Maybe if you only acquired your home entertainment equipment from dumpsters you'd conclude that aluminum electrolytics are bad? I recently escaped from a company that does aero (but not space) systems. They get mounted on aircraft and are expected to survive being shipped in an unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum electrolytic will dry out, but a tantalum will be fine. There are even wet-slug tantalums for high-altitude applications that will not dry out at these altitudes. Wet-slug tants are expensive (do they still have silver cases?) but don't blow up like the dry ones. The dry slugs coat the sintered tantalum (fuel) with MnO2 (oxidizer). snip Silver cased wet slug tantalums DO explode, most contracts that allow the use of wet slugs require the use of tantalum cased parts. |
In article ,
Dr. Anton.T. Squeegee wrote: In article , says... snippety from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? The ONLY problems I've ever had with tantalums are whe (1) The part was defective from the manufacturer. (2) The voltage rating was consistently exceeded. (3) The thing was installed backwards (reverse polarity). I have no less than five Tektronix O-scopes here, all vintage late-70's to mid-80's. This means not one of them is less than 20 years old. They all use lots of tantalums, and they all work great, but then again Tek was (in those days) proud of what they put out, and was most definitely engineer-driven (which means at least a 20% 'fudge factor' built into everything they made). Tantalum caps are very stable and durable, but they are much more costly than aluminum types. In consumer electronics, the manufacturers will try to shave every penny they can off the cost of the design, often contrary to good common (engineering) sense. Such considerations are (usually) not so critical when it comes to non-consumer stuff. Tektronix was, during that time, strongly discouraging all new designs from using tantalums. IIRC they had been taken to court over a case in which a 465 'scope (the original, not the plastic follow-ons) had spontaneously ignited and had resulted in an expensive fire. Forensics revealed that a tantalum power-supply bypass cap had started the conflagration. The drive to reduce tantalum usage was driven primarily by this liability issue, more than component cost. If you wanted to use a tantalum, you had to justify its usage to the component/design review committees -- which wasn't difficult if you had good reasons and your design was solid. -frank (ex-Tekie) -- |
In rec.radio.amateur.homebrew Ken Finney wrote:
Silver cased wet slug tantalums DO explode, most contracts that allow the use of wet slugs require the use of tantalum cased parts. Some years ago I wandered into one of the design labs to ask some questions about a new thingy we were doing. On a bench was a metal trash can with wires leading to a power supply, thermometer, and a chart recorder. "What's all this", I ask. "Getting some real data on stressing tantalums. The trash can is a blast shield just in case" was the answer. Just after the guy running the test uttered the words "looks like nothing bad is going to happen" the cap exploded with the trash can acting as a megaphone for the bang and director for the shrapnel; everyone around hit the deck. We got off the floor and looked up to the acoustical ceiling where there was capacitor pieces and an alligator clip embedded therein. When the guy running the test said "Maybe we had better rethink this design", I decided to go back to my lab and come back on a better day. We continued to use tantalums (aerospace), but there were a lot more explosions in the lab to make sure they didn't happen on the shipped product. -- Jim Pennino Remove -spam-sux to reply. |
In article , OK1SIP
writes Hi all, tantalum caps seem to be too expensive for consumer-grade equipment. They contain pricey material - silver and, of course, tantalum, so making them cheaper is impossible. AFAIK they are widely used in military-grade equipment, where the price is not an issue. Their main advantages are a longer life (they do not dry out nor leak) and a bigger temperature range (frost resistance). About using cheap parts in consumer electronics: At least 80 percent of failures of certain types of TV sets were caused by dried-out aluminum caps. The good practice when repairing these sets was: first check all electrolyte caps by adding a good one in parralel. It was successful very often. BR from Ivan The observations are consistent with the view that electrolytic capacitor reliability decreases within a short time most other components have failure modes that take a much longer time to reach the end of the bathtub. -- ddwyer |
In article , Fred
writes "Jeroen" wrote in message ... John Larkin wrote: I think multilayer ceramics are pushing 100 uF these days. Yes, but alas, only with zero volts across them. Capacitance drops precipitously with DC bias. For a cap with Y5V dielectric, at half the rated DC voltage, there's only 10% of the initial capacitance left. Most manufacturers don't tell you. The high k types vary to +-10% and +20-80% from memory if full temp is allowed for. High K doped with piezo material, they can be heard to click if hit with a square wave. |
In article , Mike Andrews
writes Some years ago I wandered into one of the design labs to ask some questions about a new thingy we were doing. On a bench was a metal trash can with wires leading to a power supply, thermometer, and a chart recorder. [snip] We got off the floor and looked up to the acoustical ceiling where there was capacitor pieces and an alligator clip embedded therein. When the guy running the test said "Maybe we had better rethink this design", I decided to go back to my lab and come back on a better day. We continued to use tantalums (aerospace), but there were a lot more explosions in the lab to make sure they didn't happen on the shipped product. Read the data books carefully. There is a formulae relating source resistance, proof voltage/actual voltage and capacitance. Note early Plessey button tantalum (very reliable) incorporated liquid conc nitric? dont blow them up! -- ddwyer |
In article , John Larkin
writes Wet-slug tants are expensive (do they still have silver cases?) but don't blow up like the dry ones. The dry slugs coat the sintered tantalum (fuel) with MnO2 (oxidizer). As I mentioned elsewhere some wet slug used conc nitric as the electroyte (from memory 35 years ago) but very reliable. -- ddwyer |
I've seen more than one problem with high-value ceramics causing problems
during operational vibe tests because of microphonics. In our case it usually seems to be the vibration causing capacitance change rather than true piezoelectricity, but it happens in any case. The last one that I remember we replaced the ceramic caps with back-to-back tantalums, in fact. Worked like a charm. "ddwyer" wrote in message ... In article , Fred writes "Jeroen" wrote in message ... John Larkin wrote: I think multilayer ceramics are pushing 100 uF these days. Yes, but alas, only with zero volts across them. Capacitance drops precipitously with DC bias. For a cap with Y5V dielectric, at half the rated DC voltage, there's only 10% of the initial capacitance left. Most manufacturers don't tell you. The high k types vary to +-10% and +20-80% from memory if full temp is allowed for. High K doped with piezo material, they can be heard to click if hit with a square wave. |
I read in sci.electronics.design that Bill Turner
wrote (in ) about 'Tantalum caps.', on Thu, 22 Jan 2004: Consumer electronics are costed down to the lowest possible level. If they can use something cheaper, they WILL use something cheaper. A TV set or VCR has had people go over the design hundreds of times with BOMs and catalogs, checking to see if they can shave a penny here or a penny there. _________________________________________________ ________ Well, maybe. Any manufacturer who has been nailed with thousands of dollars in warranty costs caused by saving a penny might disagree with your statement. I've seen it happen. Epidemic faults were, in my experience, rarely caused by cost-reduction but either by component manufacturing faults (noisy tantalum caps and unreliable fuses, for example) or by unrecognized 'gotchas' in the original circuits (high-Q series resonance in a loudspeaker crossover filter). -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
I read in sci.electronics.design that OK1SIP
wrote (in ) about 'Tantalum caps.', on Wed, 21 Jan 2004: tantalum caps seem to be too expensive for consumer-grade equipment. They contain pricey material - silver and, of course, tantalum, No. We used quite a lot of tantalum 'bead' caps in consumer audio and TV until we found the problems they have and we could get aluminium electrolytics 'with no added salt', so they didn't leak and were much more reliable. I still have some boards with them fitted. The problem with Al caps drying out is mainly that people let them get too hot. They were rated at 75 C or 85 C *max. ambient*, not 'temperature rise'. It's still a problem; we have 'designer' set-top boxes with no ventilation, and service people put 130 C rated Al caps in them as replacements; 105 C rated is often not good enough! -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
In article ,
says... Hi, Frank, Tektronix was, during that time, strongly discouraging all new designs from using tantalums. IIRC they had been taken to court over a case in which a 465 'scope (the original, not the plastic follow-ons) had spontaneously ignited and had resulted in an expensive fire. Forensics revealed that a tantalum power-supply bypass cap had started the conflagration. The drive to reduce tantalum usage was driven primarily by this liability issue, more than component cost. If you wanted to use a tantalum, you had to justify its usage to the component/design review committees -- which wasn't difficult if you had good reasons and your design was solid. Wow! I didn't know this... Thanks for the neat bit of history. I will add that most of the tantalums I'm finding in my gear are localized filters for the power-input traces in 7000-series O-scope plug-ins. Everything still works great, though. ;-) -- Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute (Known to some as Bruce Lane, KC7GR) kyrrin a/t bluefeathertech d-o=t c&o&m Motorola Radio Programming & Service Available - http://www.bluefeathertech.com/rf.html "Quando Omni Flunkus Moritati" (Red Green) |
Frank Miles wrote:
Tektronix was, during that time, strongly discouraging all new designs from using tantalums. IIRC they had been taken to court over a case in which a 465 'scope (the original, not the plastic follow-ons) had spontaneously ignited and had resulted in an expensive fire. Forensics revealed that a tantalum power-supply bypass cap had started the conflagration. The drive to reduce tantalum usage was driven primarily by this liability issue, more than component cost. If you wanted to use a tantalum, you had to justify its usage to the component/design review committees -- which wasn't difficult if you had good reasons and your design was solid. -frank (ex-Tekie) I was there at the time, too. Tantalums were essentially verboten unless the source impedance supplying the tantalum cap was at least 3 ohms/volt. That's because it was found that the short circuit failure mode was aggravated by high inrush current, so the source current had to be limited. One of the chief reasons we had been using tantalums in the first place is that they have very good bypass characteristics up to quite high frequencies -- so a single capacitor could handle a very wide range. When the source impedance was high, the capacitor didn't need to be so good in the first place, and of course adding a physical resistor in series with a supply bypass pretty much defeats the whole purpose. Consequently, the 3 ohms/volt rule pretty much eliminated tantalums as a viable choice for most applications. Fortunately, it was at just about the same time that very big improvements were made in aluminum capacitor technology. As the aluminums shrunk in size, they became much better at bypassing higher frequencies. So they took over from tantalums pretty rapidly. There was a glitch for a while, though -- boards were being cleaned with Freon at the time, and it was discovered that Freon could migrate past the seals on some or most aluminum capacitors and corrode the aluminum, leading to poor reliability. The solution adoped by some manufacturers was to add a rubber seal at the lead end of the capacitor. That increased the length of the leads between the outside of the capacitor and the inner body, increasing the lead inductance and decreasing the capacitor's high frequency bypass capability. . . but that's just another example of the day-to-day problems an engineer faces and has to overcome. Incidentally, I got a Tek 1502 TDR on eBay not long ago. It had a shorted tanalum power supply bypass capacitor. A couple of other anecdotes -- A time base plugin I designed had gotten through the entire extensive pre-production test phases, accelerated life tests, etc., and was in pilot production. I walked past the production line technician's bench every day, and began noticing several tantalum capacitors of the same type in the replaced-component box. They had come from a sweep circuit I had essentially copied from an instrument which had been in production for some time. Puzzled, I analyzed the circuit carefully, and discovered that at an extreme setting of one control, the tantalum cap could have a very small reverse voltage applied. I modified the circuit to eliminate the possibility of any reverse voltage of any level, and the capacitors quit failing. Servicing data from the instrument I had copied the circuit from showed noticeably reduced reliability of the capacitor, also. The lesson learned is that tantalums won't tolerate _any_ reverse voltage. If they don't fail immediately, a disproportionate number will fail eventually. The other anecdote involves a QRP rig. As a crude reverse-voltage protection, I had reverse-connected a 3-watt diode (actually, a 36 volt zener I had lots of) across the power supply terminals. My battery supply normally had an-line fuse which would blow. Just before Field Day one year, the fuse holder broke and I didn't have a spare in the junk box. I'd never blown a fuse in 20 years of Field Days, so went without. The battery was a 12 volt, 5 Ah sealed lead acid unit, capable of a few hundred amps if shorted. As I'm sure you've guessed, that was to be The Year of the Reverse Connected Supply. The wires to the battery immediately melted out of their insulation, burning some holes in the tent floor. I managed to disconnect the battery without getting burned and before a real fire started, and checked the damage. The rig's (recently installed) power switch was fortunately off, so the innards didn't get any reverse voltage. The diode had gotten so hot that the plastic case had fractured and probably burned -- it was gone. The diode's solder joints had melted, and the two separated diode leads were dangling. But there was still a dead short across the terminals -- a small 6.8 uF dipped tantalum capacitor was also across the terminals, and it had become such a good short that it hadn't gotten hot enough to explode. (The power supply wires were something like #24 or #26, so they'd limited the current.) My guess is that it went short just as soon as the diode opened, and made a better quality short than the diode had. The fuse is now back in place (along with new diode and capacitor), so of course I haven't reverse connected the supply since. Roy Lewallen, W7EL |
Consumer electronics are costed down to the lowest possible level. If
they can use something cheaper, they WILL use something cheaper. A TV Well, maybe. Any manufacturer who has been nailed with thousands of dollars in warranty costs caused by saving a penny might disagree with your statement. I've seen it happen. Caused by bad engineering (or purchasing), I would say. "Costing down" does not mean "making inappropriate component substitutions", and I wasn't suggesting or advocating such a policy. It means, quite simply, going over the circuit and seeing where a cheaper design or a cheaper, _compatible_ substitute can be used. If the device has a 12 month warranty, and it dies after that period expires, then nobody really cares which component was the first to fail. Especially in disposable consumer electronics! |
"Roy Lewallen" wrote in message
... analyzed the circuit carefully, and discovered that at an extreme setting of one control, the tantalum cap could have a very small reverse voltage applied. I modified the circuit to eliminate the possibility of any reverse voltage of any level, and the capacitors quit failing. How much voltage? We talking tens, hundreds, or thousands of mV? |
Walter Harley wrote:
"Roy Lewallen" wrote in message ... analyzed the circuit carefully, and discovered that at an extreme setting of one control, the tantalum cap could have a very small reverse voltage applied. I modified the circuit to eliminate the possibility of any reverse voltage of any level, and the capacitors quit failing. How much voltage? We talking tens, hundreds, or thousands of mV? As I recall, it was a couple of tenths of a volt. The capacitor was probably a 12 or 25 volt unit. A quick scan of the web shows that some manufacturers claim their tantalum capacitors will withstand something like 10% of rated voltage (not to exceed 1 volt) at 25 degrees C, and 3 - 5% of rated voltage (not to exceed 0.5 volt) at 85 degrees C, with a time limit on application of reverse voltage. Because of my experience, though, I'd consider it to be bad design practice to allow any reverse voltage at all until I saw some reliability figures for capacitors used under those conditions. The problem is that it doesn't cause immediate failure, or even assured failure -- it just increases the probability of failure. Some applications can tolerate the increased failure rate, and some can't. At Tek, a great deal of importance was placed on reliability. Roy Lewallen, W7EL |
|
"Henry Kolesnik" wrote in message ...
Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr Didn't see anyone else mention that aluminum electrolytics don't work well when cold, but tantalums keep working fine. Your test equipment probably became "obsolete" because the things being tested were newer and more sophisticated than the equipment was designed for, and therefore it was no longer needed. Technology moves along rather swiftly these days. If all analog TV signals were discontinued with only digital available, your old rear projection TV would also be obsolete. Test equipment is commonly much more sophisticated than consumer...drifts that are practically unnoticable in consumer electronics would be intolerable in test equipment. But even so, I have plenty of test equipment that's 20+ years old that still works fine. I've had to repair (or toss) a higher percentage of my consumer electronics than of my test equipment, for sure. "Discman" type CD players seem to have an especially short life, but I've had tape recorders, TVs and at least one stereo amplifier fail as well. Cheers, Tom |
On Thu, 22 Jan 2004 18:12:20 GMT, "Ken Finney"
wrote: "John Larkin" wrote in message ... On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott" wrote: I wouldn't assume that just because your test equipment comes to you broken is a result of tantalum caps -- perhaps your sample is skewed by buying at hamfests instead of burgling active technology companies? Maybe if you only acquired your home entertainment equipment from dumpsters you'd conclude that aluminum electrolytics are bad? I recently escaped from a company that does aero (but not space) systems. They get mounted on aircraft and are expected to survive being shipped in an unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum electrolytic will dry out, but a tantalum will be fine. There are even wet-slug tantalums for high-altitude applications that will not dry out at these altitudes. Wet-slug tants are expensive (do they still have silver cases?) but don't blow up like the dry ones. The dry slugs coat the sintered tantalum (fuel) with MnO2 (oxidizer). snip Silver cased wet slug tantalums DO explode, most contracts that allow the use of wet slugs require the use of tantalum cased parts. Sure, any cap will explode if you dump enough energy into it. The difference is that the dry Ta:MnO2 guys only need a tiny bit of energy to ignite, then chemically explode on their own. Just a high dV/dT will set one off. John |
I've started a new thread with a partial respnse to your comments Subject:
Tantalums and test eqpt 73 hank wd5jfr "Tom Bruhns" wrote in message ... "Henry Kolesnik" wrote in message ... Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr Didn't see anyone else mention that aluminum electrolytics don't work well when cold, but tantalums keep working fine. Your test equipment probably became "obsolete" because the things being tested were newer and more sophisticated than the equipment was designed for, and therefore it was no longer needed. Technology moves along rather swiftly these days. If all analog TV signals were discontinued with only digital available, your old rear projection TV would also be obsolete. Test equipment is commonly much more sophisticated than consumer...drifts that are practically unnoticable in consumer electronics would be intolerable in test equipment. But even so, I have plenty of test equipment that's 20+ years old that still works fine. I've had to repair (or toss) a higher percentage of my consumer electronics than of my test equipment, for sure. "Discman" type CD players seem to have an especially short life, but I've had tape recorders, TVs and at least one stereo amplifier fail as well. Cheers, Tom |
In sci.electronics.design Tom Bruhns wrote:
"Henry Kolesnik" wrote in message ... Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? snip along rather swiftly these days. If all analog TV signals were discontinued with only digital available, your old rear projection TV would also be obsolete. Test equipment is commonly much more To take this as an example, set-top boxes to act as a TV tuner will be available for a long while after analog switchoff. |
Don't mean to beat a dead topic to a second death, but in case you wanted to
know NASA uses tantalums extensively as replacements for electrolytics on-orbit (on station & shuttle). I don't can't recite the reasoning verbatim, but it is an M&P (materials and processes) issue, having to do with operating at low pressures and also the dangers of electrolytics entering various failure modes due to overheating in space (no bouyancy-driven convection). Tantalums tend not to fail catastrophically (pop or explode) when thermally stressed. Jason Dugas KB5URQ NASA-JSC "Henry Kolesnik" wrote in message ... Over the last few years I've acquired quite a few consumer electronincs pcbs including TVs, VCRs, stereos, etc, so when I discovered that I needed a tantalum to repair some test equipment I was going to salvage a tantalum. I couldn't find one anywhere, so I assume they're too expensive or too unrelaible for high end consumer electronics. A couple of the boards were from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? tnx hank wd5jfr |
Frank Miles wrote:
In article , Dr. Anton.T. Squeegee wrote: In article , says... snippety from my personal stuff purchased new. One example is a MGA Mitsubishi rear projection TV that operated flawlessly for nearly 20 years of daily use. Most of my test equipment comes from hamfests and is surplus after becoming obsolete and non-operative in less than 20 years. That leads me to wonder what the real story is behind tantalum capacitors. What do the experts have to say? The ONLY problems I've ever had with tantalums are whe (1) The part was defective from the manufacturer. (2) The voltage rating was consistently exceeded. (3) The thing was installed backwards (reverse polarity). I have no less than five Tektronix O-scopes here, all vintage late-70's to mid-80's. This means not one of them is less than 20 years old. They all use lots of tantalums, and they all work great, but then again Tek was (in those days) proud of what they put out, and was most definitely engineer-driven (which means at least a 20% 'fudge factor' built into everything they made). Tantalum caps are very stable and durable, but they are much more costly than aluminum types. In consumer electronics, the manufacturers will try to shave every penny they can off the cost of the design, often contrary to good common (engineering) sense. Such considerations are (usually) not so critical when it comes to non-consumer stuff. Tektronix was, during that time, strongly discouraging all new designs from using tantalums. IIRC they had been taken to court over a case in which a 465 'scope (the original, not the plastic follow-ons) had spontaneously ignited and had resulted in an expensive fire. Forensics revealed that a tantalum power-supply bypass cap had started the conflagration. The drive to reduce tantalum usage was driven primarily by this liability issue, more than component cost. If you wanted to use a tantalum, you had to justify its usage to the component/design review committees -- which wasn't difficult if you had good reasons and your design was solid. Ah ha! I have a 465 (w/DM44) that I purchased in 1978 for personal use (no commercial abuse). Shortly after the warranty expired, it would not power up. I traced the problem to a shorted tantalum filter cap on the +15 volt line. But of course, it wasn't in the power supply, but rather on one of the boards. Pain to get to, IIRC. BTW, I did not get option 5 (TV sync separator). I wonder if it is feasable to install it myself? Documentation is listed as 465 option 5 supplement 070-2191-00. Anyone have this info? -- Jerry wa2rkn no email @ present |
| All times are GMT +1. The time now is 02:59 PM. |
|
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com