On Sat, 20 Jun 2020 05:56:48 -0500, amdx <nojunk@knology.net> wrote:
>On 6/19/2020 8:36 AM, jlarkin@highlandsniptechnology.com wrote:
>> On Fri, 19 Jun 2020 04:04:33 -0700 (PDT), amdx62@gmail.com wrote:
>>
>>> On Sunday, June 14, 2020 at 6:31:16 AM UTC-5, Tim Williams wrote:
>>>> https://www.eevblog.com/forum/metrology/film-and-ceramic-capacitor-leakage-current/
>>>>
>>>> Tim
>>>>
>>>> --
>>>> Seven Transistor Labs, LLC
>>>> Electrical Engineering Consultation and Design
>>>> Website: https://www.seventransistorlabs.com/
>>>
>>>
>>> I'm sure many have seen this, but for those that haven't it I interesting.
>>> https://www.electronicdesign.com/technologies/test-measurement/article/21773611/whats-all-this-teflon-stuff-anyhow
>>> Mikek
>>
>> Electronic Design is pitiful. I received the printed mag yesterday; I
>> have no idea why. The entire issue isn't much thicker than a business
>> card. The few articles are pitiful, mostly blather about silly
>> software. The online version is unbearable.
>>
>
> I think you have mentioned this before. It seems with the internet
>revolution, most print media has gone downhill, even my local newspaper
>has shrunk in pages and in physical dimensions.
> But that's a different subject, I presented the link to show info
>about Teflon, that I thought was interesting. I do think I originally
>saw the write up in a different source, but when I searched, this is the
>source I found. Sorry it set you off!
It's a discussion group. We need stuff to discuss, ideally on the
topic of electronics.
> I suggest you unsubscribe and don't read the online version of
>Electronic Design.
I have no idea why they have started mailing me the silly skinny mag.
I don't look at their online version any more. It's annoying and
useless.
I do need to keep current on what's happening. The mags (ED, EDN, EE
Times, Electronics Weekly, All About Circuits) are barely worth a
quick glance, and some are so loaded up with web tricks that they are
unbearable. Why does anyone need 35 cookies?
Once a month roughly, I cruise the various semiconductor web sites and
look at the new product listings. Digikey and Mouser have new product
pages too.
Any other ideas on how to keep up to date? One would think that such a
giant industry as ours would support at least one decent mag.
The optics mags are still fat and good, full of ads and articles and
product releases. As are the microwave mags, but I don't do RF (ie,
narrowband frequency domain) much, so only a fraction of their content
is useful to us.
Repeated rant: the DC specs of RF parts are usually terrible.
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by ●June 19, 20202020-06-19
On Fri, 19 Jun 2020 04:04:33 -0700 (PDT), amdx62@gmail.com wrote:
Electronic Design is pitiful. I received the printed mag yesterday; I
have no idea why. The entire issue isn't much thicker than a business
card. The few articles are pitiful, mostly blather about silly
software. The online version is unbearable.
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by ●June 19, 20202020-06-19
On Sunday, June 14, 2020 at 6:31:16 AM UTC-5, Tim Williams wrote:
> 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.
I noticed that too, in pH meter inputs. Teflon had low leakage but high
triboelectric charge generation.
Ever seen demo set ups for ESD generation? They place a metal plate on
top of a teflon block, then press (or slide) it, then pull it up.
Kilovolts get generated (big sparks). Teflon seen to be very (negative
charge) triboelectric, see
https://en.wikipedia.org/wiki/Triboelectric_effect
Reply by Jasen Betts●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.
Reply by Tauno Voipio●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 Mikko OH2HVJ●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 Chris Jones●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 Chris Jones●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 Chris Jones●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.