BinaryMike
Pelagic EE
This is such a frequent topic of discussion that I thought it would be worthwhile to post this item out of an EE rag dating 1959.
Paper/Oil Capacitor Life Info
- Thread starter BinaryMike
- Start date
That was just an example based on the test. What I get from that are a couple of things
1) plastic film and mica caps last longer than PIO
2) cooler temperatures make them last longer
3) lower voltages make them last longer
I wonder what effect simple aging has on them. I don't expect the engineers really spent a lot of time considering what the effects of sitting un-used for 50 years would be.
1) plastic film and mica caps last longer than PIO
2) cooler temperatures make them last longer
3) lower voltages make them last longer
I wonder what effect simple aging has on them. I don't expect the engineers really spent a lot of time considering what the effects of sitting un-used for 50 years would be.
primosounds
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Right. The article seems to validate that the hermetically sealed (glass end sealed) pio caps would have an extremely long shelf life if unused. And used ones would be reliable for many years if they have not been overheated or over voltaged. I don't reuse caps so not an issue for me. I am not saying pio are the best caps or best sounding, but for the price they are hard to beat.
I have some in use, all of them old and purchased NOS, but I'm definitely not wedded to them. They're big for the value so they don't always fit. My Bogen MO-100A's run PIO because I had the values on hand and had just enough room to put them in there. I think I stuck a pair in my Pilot SA-260 for the same reason. The caps that were in the Pilot sounded dreadful, the PIO caps smoothed it out considerably.
While it gives a good indication of some of the factors in play, that's an old formula which
The more modern formula used by CDE and IC (same company now, I think), among others, is:
The problem with gauging lifespan for older capacitors is that the materials degrade when not used. The kraft paper used in PIO, for example, began life as ground up trees. The treatment process left behind acidic residue which degrades the paper and the metal components, and the oils used were vegetable (typically castor oil or other vegetable oil) which polymerize over time and the ESR climbs. The more oxygen gets in, the worse it is. This is why the quality of the vent, poor in the old days, matters. If the plus is natural rubber it leaks. This problem, BTW, continues to exist. Many of the counterfeit capacitors use natural rubber or latex plugs instead of silicone, elastomer, or other synthetics. Over time the plug hardens and shrinks, and this permits the entry of air and the evaporation of electrolyte.
The dielectric absorption (DA) for older capacitors is very high, so electrons migrate into the dielectric and then slowly migrate out when the field is reversed. This averages the signal being applied to the capacitor with its signal history. Something most proponents of older capacitors simply do not understand. This is why A/D and D/A circuitry requires capacitors with low DA. The DA issue, BTW, can injure or kill with a high-voltage capacitor. Even though voltage has been removed and the capacitor "discharged", some charge remains and it gradually leaks out. This is why capacitors are stored with a wire across the terminals. It prevents any danger from residual charge.
Modern capacitors from CDE, IC, etc. are rated for a maximum lifespan of about 15 years. So the "theoretical" lifepsan of 50+ years is nonsense. A change in value of 20% or greater is deemed to be failure, so definitional issues may account for the difference, but I think it was a lack of knowledge. Old capacitors have no Magickal Mojo, they just have high ESR, high DA, high distortion, poor tolerances, and materials prone to fail.
Eh. This was probably more than anyone wanted to read.
(a) does not include the load life-rating
(b) does not account for the effects of ripple current.
It uses a testing-time duration fudge factor instead of the modern fudge factor for lifespan estimation. (b) does not account for the effects of ripple current.
The more modern formula used by CDE and IC (same company now, I think), among others, is:
Given:
// Capacitor Parameters
L1 = Load life rating
L2 = Operating Life at temperature Ta
Vr = Rated voltage
Tm = maximum rated temperature
// Environmental Parameters
Vo = Applied voltage
Vr = Ripple voltage
Ta = Ambient temperature
Tr = Temperature rise due to ripple current
Then:
L2 = L1 x (Vr / Vo) x 2^[(Tm - (Ta + Tr)) / 10]
You can see how as Ta approaches Tm the lifespan drops, and how as it moves away from Tm the lifespan increases. But what is key here is that the ripple current heating, Tr, is also reducing lifespan. So, all other factors being within specification, even if the ambient temperature is not high, the ripple current heating can destroy the capacitor. This is one of the secrets of power supplies.// Capacitor Parameters
L1 = Load life rating
L2 = Operating Life at temperature Ta
Vr = Rated voltage
Tm = maximum rated temperature
// Environmental Parameters
Vo = Applied voltage
Vr = Ripple voltage
Ta = Ambient temperature
Tr = Temperature rise due to ripple current
Then:
L2 = L1 x (Vr / Vo) x 2^[(Tm - (Ta + Tr)) / 10]
The problem with gauging lifespan for older capacitors is that the materials degrade when not used. The kraft paper used in PIO, for example, began life as ground up trees. The treatment process left behind acidic residue which degrades the paper and the metal components, and the oils used were vegetable (typically castor oil or other vegetable oil) which polymerize over time and the ESR climbs. The more oxygen gets in, the worse it is. This is why the quality of the vent, poor in the old days, matters. If the plus is natural rubber it leaks. This problem, BTW, continues to exist. Many of the counterfeit capacitors use natural rubber or latex plugs instead of silicone, elastomer, or other synthetics. Over time the plug hardens and shrinks, and this permits the entry of air and the evaporation of electrolyte.
The dielectric absorption (DA) for older capacitors is very high, so electrons migrate into the dielectric and then slowly migrate out when the field is reversed. This averages the signal being applied to the capacitor with its signal history. Something most proponents of older capacitors simply do not understand. This is why A/D and D/A circuitry requires capacitors with low DA. The DA issue, BTW, can injure or kill with a high-voltage capacitor. Even though voltage has been removed and the capacitor "discharged", some charge remains and it gradually leaks out. This is why capacitors are stored with a wire across the terminals. It prevents any danger from residual charge.
Modern capacitors from CDE, IC, etc. are rated for a maximum lifespan of about 15 years. So the "theoretical" lifepsan of 50+ years is nonsense. A change in value of 20% or greater is deemed to be failure, so definitional issues may account for the difference, but I think it was a lack of knowledge. Old capacitors have no Magickal Mojo, they just have high ESR, high DA, high distortion, poor tolerances, and materials prone to fail.
Eh. This was probably more than anyone wanted to read.
Any idea what dielectric and oil is used in modern PIOS?
Nope.
Instead of speculating, consulting datasheets (reading is fundamental) would be useful.
Briefly, and again, a vast difference exists between a properly fabricated modern capacitor, constructed from inert plastics, and fifty year old paper capacitors which suffer from chemical deterioration and had terrible properties when new.
I say "properly fabricated" because I've elsewhere explained the capacitor plague for modern electrolytics which occurred in the late 1990s. This resulted from a stolen electrolyte formula, lacking in anti-corrosion and other additives, consequently causing millions of capacitors on computer motherboards to prematurely fail. I owned three of them at the time, made by Asus and other reputable manufacturers. The cans bulged or burst, and it caused worldwide consternation and upset. Manufacturers refused to help those who had purchased the defective products because the one year warranty had expired.
The lifespan of capacitor depends, in part, upon such factors as Ohmic heating AND loss of electrolyte AND deterioration of the electrolyte AND corrosion of the metal plates and/or connections AND alteration of the oxide layer AND other factors. At maximum temperature, and you could trivially verify this, a capacitor's lifespan is not less than 1,000 and not more than 10,000 hours, typically hovering around 1,000 to 2,000 hours for most modern parts.
Lowering the temperature improves the lifespan of modern capacitors because it prevents loss of electrolyte. It does not appreciably affect the lifespan of older capacitors which, as I noted, have poor seals, chemical corrosion of the paper, chemical alteration of the oil, etc. They were used up sitting on the shelf, even NOS. The oxide layer has deformed from lack of use, as well. (Yes, it could be reformed but this implies the electrolyte is still functioning and that deterioration has not occurred, which it unfortunately has.)
Power supplies in modern equipment are often always on, or on to some extent, to allow remote controls to function. The lifespan of capacitors is far fewer years (or days) than you might expect.
But the issue, again, is old capacitors which were garbage when new and have hardly improved in fifty years. The sound of them is horrible, full of non-linear (voltage and frequency dependent) resistance and distortion.
The oil varies.
By "modern" you mean extant or legally permitted? Because capacitors routinely used PCBs until about banned worldwide circa 2000. The USA was ahead of the curve, banning them in 1979. Many of the older, and leaky, PIO motor-start capacitors beloved by audiophiles used PCBs. Yeah, think about that next time someone shows you the old, greasy motor-start capacitors they plan to use. Mmmm, tasty distortion AND delicious PCBs. Mmmmmm.
Of current manufacture it is either synthetic mineral (reformulated petroleum) oils or siloxanes (silicone) oils with various additives.
BUT, having written that, many capacitors that are today sold are inexpensive or counterfeits of name brands. Such capacitors use anything inexpensive for the oil, including vegetable oils not suitable for human consumption. The only way to reduce cost is to lie: thinner metals, thinner insulators, poor quality metals, poor quality electrolytes, etc. China is notorious for putting such components into the supply stream where they fail. Nobody knows what cheap (as in shoddy) materials will be used for manufacture that week.
I was thinking Mundorf specifically.
I know they have oil variants.
I thought they were marketing a PIO maybe recently discontinued. I didn't find in a recent search
I know they have oil variants.
I thought they were marketing a PIO maybe recently discontinued. I didn't find in a recent search
toxcrusadr
Omelette au Fromage
I too am curious what they are using. Likely a hydrocarbon mineral oil of some type I would think. Mundorf's data sheet only says the oil is 'specially formulated'. One would hope they would at least give a general class (mineral oil, silicone, free range emu back fat)..
http://www.mundorf.com/english 1.1/kondensatoren.htm
http://www.mundorf.com/english 1.1/kondensatoren.htm
primosounds
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No need for the scare tactics and while there is no doubt that pcbs were used in the past, i have yet to see a vintage pio cap with its body exploded and toxic material leaking and this after 25+ years of fooling with tube amps. Name brand type pio caps made in the usa are extremely reliable and well made. It is the reason they are used in vintage military equiipment. The military during the 50s and all throughout the cold war years, had pretty much a free reign on choosing or designing components for its needs and yet vitaminQ and the other analogous brands are the signal caps that are ubiquitous.
Certain precautions should be observed while handling these type of materials and as long as they are not leaking the danger is probably less than changing the motor oil in your car.
toxcrusadr
Omelette au Fromage
Correct. The only real danger is if they actually leak.
I have a whole box of old metal can oil caps and 95% of them read spot on after all this time. Of course the metal can is the secret - air can't get in, oil can't get out, it's a very stable environment.
I have a whole box of old metal can oil caps and 95% of them read spot on after all this time. Of course the metal can is the secret - air can't get in, oil can't get out, it's a very stable environment.
Well, I'm not exactly engaging in "scare tactics" and my statement was qualified for motor-start capacitors, not signal capacitors, although some of them may have used PCBs. I have not studied that part of the issue beyond a cursory reading.
Leaky motor-start capacitors are common, and this was the point I was making when I specifically addressed them:
Many of the older, and leaky, PIO motor-start capacitors beloved by audiophiles used PCBs. Yeah, think about that next time someone shows you the old, greasy motor-start capacitors they plan to use. Mmmm, tasty distortion AND delicious PCBs. Mmmmmm.
I was not referring to small signal capacitors which likely did not use PCBs.
My point is true and factual: older PIO capacitors used PCBs and these are now banned as hazardous. Anyone may do their own research as to the level of exposure that would be considered safe.
I'm confused about the discussion of electrolyte in the context of PIO caps?
In posting No. 8 the question was asked about the oil used in PIO capacitors.
Capacitor discussions, like those about food, politics, religion, and traffic patterns in major cities, tend to wander.
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I thought oil was an insulator, as opposed to conductive electrolyte used in electrolytic capacitors (which don't use oil to my knowledge) from which they get their name.
Sprague Vitamin Q PIO caps used mineral oil. Pyramid and some other small signal PIO caps from the same era did use PCBs, so you should exercise caution (since PCBs bio-accumulate, they can build up in your body in fat cells).
[EDIT] just read up on PCB skin absorption after reading Retrovert's comments - depending on the variety of PCB (and I don't know what type is used in capacitors), skin absorption rates can actually be very high, so ignore my previous advice. If you suspect you have caps with PCBs and they are leaking, keep your distance!
-D
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You are correct, it is an insulator.
Again, someone asked for information about PIO capacitors. See Posting No. 8.
