You might find the Telco’s use Teflon caps for ADSL splitters to minimize leakage load on -48V CO batteries.
Some capacitor leakage measurements
Started by ●June 14, 2020
Reply by ●June 17, 20202020-06-17
Reply by ●June 17, 20202020-06-17
On Wednesday, June 17, 2020 at 2:38:22 PM UTC-4, John Larkin wrote:> On Wed, 17 Jun 2020 13:03:00 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 2020-06-17 09:02, Chris Jones wrote: > >> On 17/06/2020 17:14, Cydrome Leader wrote: > >>> Chris Jones <lugnut808@spam.yahoo.com> wrote: > >>>> On 15/06/2020 12:12, Phil Allison wrote: > >>>>> jla...@highlandsniptechnology.com wrote: > >>>>> > >>>>> ========================================= > >>>>> > >>>>>> > >>>>>> Somebody here once measured self-discharge of some film caps, over > >>>>>> years. I recall discharge levels something like one per cent per year. > >>>>>> > >>>>> > >>>>> ** Must have been some large value polystyrene types. > >>>>> > >>>>> Lowest tempco and leakage of any film cap. > >>>> > >>>> Teflon might be lower leakage, but the only sources I know of are > >>>> surplus USSR parts on ebay that are usually physically huge and of > >>>> unknown and probably quite adventurous history, or by slaughtering a > >>>> Tektronix scope, which ought to be illegal. > >>> > >>> There's still plenty of teflon film cap makers in the US. Teflon caps > >>> have > >>> high temp ratings, that's about it. It's not the end-all dielectric > >>> material. > >> > >> Yes, I had seen that there are companies that make them, however there > >> are none at Mouser and there is only one range in digi-key and the > >> largest value is 47pF, so I still consider them hard to get in higher > >> capacitance values. > >> > >> Do you know of any distributors that stock a good range of them? > >> > >> I know they are not magical, but probably have slightly less leakage > >> than polystyrene, and certainly a better combination of low leakage and > >> also withstanding soldering temperatures. > > > >Octopart doesn't have show high-value PTFE-dielectric caps in stock > >anywhere. > > > >Cheers > > > >Phil Hobbs > > Does anyone have a use for super-low-leakage caps?I wanted to try 'em in a high Q LC BP filter. Low dissipation factor is what I read. (at some point leakage will look like dissipation... I think.?*) The fact that you can't buy 'em implies there is no real market. I always wonder what's the market for the big 10 uF film panasonic caps I like. (mentioned above.) George H. *so what's the analog of charge in mechanical mass- spring system? I'm thinking the mass.> > Teflon has a horrible TC, so the voltage on a charged cap will change > with temperature. That could look like leakage, or anti-leakage. > > Interesting: is the energy conserved after a temperature cycle? > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●June 17, 20202020-06-17
On Wednesday, June 17, 2020 at 11:38:22 AM UTC-7, John Larkin wrote:> Does anyone have a use for super-low-leakage caps?Well, yeah; Keithley electrometers used a lot of 500V rated Mallory SX polystyrene caps, for low-voltage parts of their innards. I assumed that they were the good solution at that time (but you can't reflow-solder polystyrene parts very well).
Reply by ●June 17, 20202020-06-17
Chris Jones <lugnut808@spam.yahoo.com> wrote:> On 17/06/2020 17:14, Cydrome Leader wrote: >> Chris Jones <lugnut808@spam.yahoo.com> wrote: >>> On 15/06/2020 12:12, Phil Allison wrote: >>>> jla...@highlandsniptechnology.com wrote: >>>> >>>> ========================================= >>>> >>>>> >>>>> Somebody here once measured self-discharge of some film caps, over >>>>> years. I recall discharge levels something like one per cent per year. >>>>> >>>> >>>> ** Must have been some large value polystyrene types. >>>> >>>> Lowest tempco and leakage of any film cap. >>> >>> Teflon might be lower leakage, but the only sources I know of are >>> surplus USSR parts on ebay that are usually physically huge and of >>> unknown and probably quite adventurous history, or by slaughtering a >>> Tektronix scope, which ought to be illegal. >> >> There's still plenty of teflon film cap makers in the US. Teflon caps have >> high temp ratings, that's about it. It's not the end-all dielectric >> material. > > Yes, I had seen that there are companies that make them, however there > are none at Mouser and there is only one range in digi-key and the > largest value is 47pF, so I still consider them hard to get in higher > capacitance values. > > Do you know of any distributors that stock a good range of them?They're not high production items, so you skip the distributor and call the manufacturer up. Ask about surplus or overruns. makers are bycap electrocube arizona capacitor Electronic Concepts, but they suck as a company> I know they are not magical, but probably have slightly less leakage > than polystyrene, and certainly a better combination of low leakage and > also withstanding soldering temperatures.I don't have any spec sheets in front of me, but I don't recall teflon having impressive megohms/uF values. If you need high temp go teflon. For anything else, other dielectrics tend to be better. The whole shakeup over polystrene and why only one company still makes them has to do with the problem of only the highest quality plastic films can be used to make capacitors, and capacitor makers are the smallest user of plastic films. One of the above companies actually has their own plastic film production line as nobody else can make film to a usable yield. One factory I went to had a mountain of pallets of plastic film that was rejected by their QC. It was probably good film, but not good enough for capacitors.
Reply by ●June 18, 20202020-06-18
On 18/06/2020 08:11, Cydrome Leader wrote:> Chris Jones <lugnut808@spam.yahoo.com> wrote: >> On 17/06/2020 17:14, Cydrome Leader wrote: >>> Chris Jones <lugnut808@spam.yahoo.com> wrote: >>>> On 15/06/2020 12:12, Phil Allison wrote: >>>>> jla...@highlandsniptechnology.com wrote: >>>>> >>>>> ========================================= >>>>> >>>>>> >>>>>> Somebody here once measured self-discharge of some film caps, over >>>>>> years. I recall discharge levels something like one per cent per year. >>>>>> >>>>> >>>>> ** Must have been some large value polystyrene types. >>>>> >>>>> Lowest tempco and leakage of any film cap. >>>> >>>> Teflon might be lower leakage, but the only sources I know of are >>>> surplus USSR parts on ebay that are usually physically huge and of >>>> unknown and probably quite adventurous history, or by slaughtering a >>>> Tektronix scope, which ought to be illegal. >>> >>> There's still plenty of teflon film cap makers in the US. Teflon caps have >>> high temp ratings, that's about it. It's not the end-all dielectric >>> material. >> >> Yes, I had seen that there are companies that make them, however there >> are none at Mouser and there is only one range in digi-key and the >> largest value is 47pF, so I still consider them hard to get in higher >> capacitance values. >> >> Do you know of any distributors that stock a good range of them? > > They're not high production items, so you skip the distributor and call > the manufacturer up. Ask about surplus or overruns. > > makers are > > bycap > electrocube > arizona capacitor > Electronic Concepts, but they suck as a company > >> I know they are not magical, but probably have slightly less leakage >> than polystyrene, and certainly a better combination of low leakage and >> also withstanding soldering temperatures. > > I don't have any spec sheets in front of me, but I don't recall teflon > having impressive megohms/uF values. If you need high temp go teflon. For > anything else, other dielectrics tend to be better.I suspect that even if they are better, they will set the specification at the limit of what they can measure in a reasonable time period.> The whole shakeup over polystrene and why only one company still makes > them has to do with the problem of only the highest quality plastic films > can be used to make capacitors, and capacitor makers are the smallest user > of plastic films. One of the above companies actually has their own > plastic film production line as nobody else can make film to a usable > yield. One factory I went to had a mountain of pallets of plastic film > that was rejected by their QC. It was probably good film, but not good > enough for capacitors.Thanks for the interesting story. I had read somewhere that nobody was making the polystyrene film anymore and that capacitor makers who sold them were just using up old stocks of film, but I had no way of knowing if all that was true. For those in Australia, there is a company (Rockby) selling new-old-stock Evox-Rifa polystyrene capacitors, but only a few very odd values, and sometimes discounted to very cheap prices (a few cents). I bought a lifetime stock of a few values and have used a few from time to time, for peak-hold circuits etc. Not all of their polystyrene capacitors are new old stock, I took a chance by ordering one lot that did not have a manufacturer's name and part number, and those seem to be from China.
Reply by ●June 18, 20202020-06-18
On 18/06/2020 06:57, Anthony Stewart wrote:> You might find the Telco’s use Teflon caps for ADSL splitters to minimize leakage load on -48V CO batteries. >No, a nanoamp or two will not flatten their battery, so going to any effort to find a capacitor that leaks less than picoamperes is not sensible in this situation.
Reply by ●June 18, 20202020-06-18
On 18/06/2020 05:45, Phil Hobbs wrote:> On 2020-06-17 14:38, John Larkin wrote: >> On Wed, 17 Jun 2020 13:03:00 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2020-06-17 09:02, Chris Jones wrote: >>>> On 17/06/2020 17:14, Cydrome Leader wrote: >>>>> Chris Jones <lugnut808@spam.yahoo.com> wrote: >>>>>> On 15/06/2020 12:12, Phil Allison wrote: >>>>>>> jla...@highlandsniptechnology.com wrote: >>>>>>> >>>>>>> ========================================= >>>>>>> >>>>>>>> >>>>>>>> Somebody here once measured self-discharge of some film caps, over >>>>>>>> years. I recall discharge levels something like one per cent per >>>>>>>> year. >>>>>>>> >>>>>>> >>>>>>> ** Must have been some large value polystyrene types. >>>>>>> >>>>>>> Lowest tempco and leakage of any film cap. >>>>>> >>>>>> Teflon might be lower leakage, but the only sources I know of are >>>>>> surplus USSR parts on ebay that are usually physically huge and of >>>>>> unknown and probably quite adventurous history, or by slaughtering a >>>>>> Tektronix scope, which ought to be illegal. >>>>> >>>>> There's still plenty of teflon film cap makers in the US. Teflon caps >>>>> have >>>>> high temp ratings, that's about it. It's not the end-all dielectric >>>>> material. >>>> >>>> Yes, I had seen that there are companies that make them, however there >>>> are none at Mouser and there is only one range in digi-key and the >>>> largest value is 47pF, so I still consider them hard to get in higher >>>> capacitance values. >>>> >>>> Do you know of any distributors that stock a good range of them? >>>> >>>> I know they are not magical, but probably have slightly less leakage >>>> than polystyrene, and certainly a better combination of low leakage and >>>> also withstanding soldering temperatures. >>> >>> Octopart doesn't have show high-value PTFE-dielectric caps in stock >>> anywhere. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Does anyone have a use for super-low-leakage caps? >> >> Teflon has a horrible TC, so the voltage on a charged cap will change >> with temperature. That could look like leakage, or anti-leakage.Good point.> Its glass transition is right around room temperature, so CTE and other > TCs go nuts in a very inconvenient region.Yes, I noticed that when I was looking into phase-stable cables for a VNA. Also I suspect that other dielectrics may be better for microwave PCBs in measuring instruments where stability over temperature is important. I guess you could also ovenize everything at a higher temperature, where the TC is lower.
Reply by ●June 18, 20202020-06-18
George Herold <ggherold@gmail.com> writes:> The fact that you can't buy 'em implies there is no > real market. I always wonder what's the market for the > big 10 uF film panasonic caps I like. (mentioned above.)Anything that requires long assured lifetime, like automotive, industrial and medical. Check out the service life of electrolytics in elevated temperatures - even with lifetime temperature scaling, would you accept those for your cars brake or steering system ? -- mikko
Reply by ●June 18, 20202020-06-18
On 17.6.20 16:02, Chris Jones wrote:> On 17/06/2020 17:14, Cydrome Leader wrote: >> Chris Jones <lugnut808@spam.yahoo.com> wrote: >>> On 15/06/2020 12:12, Phil Allison wrote: >>>> jla...@highlandsniptechnology.com wrote: >>>> >>>> ========================================= >>>> >>>>> >>>>> Somebody here once measured self-discharge of some film caps, over >>>>> years. I recall discharge levels something like one per cent per year. >>>>> >>>> >>>> ** Must have been some large value polystyrene types. >>>> >>>> Lowest tempco and leakage of any film cap. >>> >>> Teflon might be lower leakage, but the only sources I know of are >>> surplus USSR parts on ebay that are usually physically huge and of >>> unknown and probably quite adventurous history, or by slaughtering a >>> Tektronix scope, which ought to be illegal. >> >> There's still plenty of teflon film cap makers in the US. Teflon caps >> have >> high temp ratings, that's about it. It's not the end-all dielectric >> material. > > Yes, I had seen that there are companies that make them, however there > are none at Mouser and there is only one range in digi-key and the > largest value is 47pF, so I still consider them hard to get in higher > capacitance values. > > Do you know of any distributors that stock a good range of them? > > I know they are not magical, but probably have slightly less leakage > than polystyrene, and certainly a better combination of low leakage and > also withstanding soldering temperatures.Teflon (PTFE) is notoriously microphonic. Years ago I made a femtoampere-class electrometer, and when testing it the output swinged back and forth at a leisurely rate. The swinging happened synchronously with the movements of the Teflon-insulated input coaxial cable. -- -TV
Reply by ●June 18, 20202020-06-18
On 2020-06-17, Anthony Stewart <tony.sunnysky@gmail.com> wrote:> You might find the Telco’s use Teflon caps for ADSL splitters to minimize leakage load on -48V CO batteries.I can't see why they'd need a less leaky capacitor there than the much larger ones they use for the ringers in phones. -- Jasen.
