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Film capacitor insulation resistance spec.

Started by Yzordderrex August 2, 2016
Greetings,

I am having difficulty interpreting insulation resistance spec.  It is on first page.  IR C >400 sec. .....


http://datasheets.avx.com/cb-petht.pdf

Can someone interpret?


Thanks,
Bob
N9NEO
On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote:
> Greetings, > > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... > > > http://datasheets.avx.com/cb-petht.pdf > > Can someone interpret? > > > Thanks, > Bob > N9NEO
I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? m
On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote:
> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: > > Greetings, > > > > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... > > > > > > http://datasheets.avx.com/cb-petht.pdf > > > > Can someone interpret? > > > > > > Thanks, > > Bob > > N9NEO > > I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? > > m
Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. Seems simple enough. George H.
On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote:
> Greetings, > > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... > > > http://datasheets.avx.com/cb-petht.pdf > > Can someone interpret? > > > Thanks, > Bob > N9NEO
Ok. Thanks. My boss will probably want me to call AVX and get a number. I will report back to group.
On Tue, 2 Aug 2016 06:55:52 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote: >> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: >> > Greetings, >> > >> > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... >> > >> > >> > http://datasheets.avx.com/cb-petht.pdf >> > >> > Can someone interpret? >> > >> > >> > Thanks, >> > Bob >> > N9NEO >> >> I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? >> >> m > >Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. >Seems simple enough. > >George H.
Some guy here once posted measured time constants of some film caps. The numbers were in years, or possibly centuries. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Tue, 02 Aug 2016 08:29:10 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Tue, 2 Aug 2016 06:55:52 -0700 (PDT), George Herold ><gherold@teachspin.com> wrote: > >>On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote: >>> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: >>> > Greetings, >>> > >>> > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... >>> > >>> > >>> > http://datasheets.avx.com/cb-petht.pdf >>> > >>> > Can someone interpret? >>> > >>> > >>> > Thanks, >>> > Bob >>> > N9NEO >>> >>> I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? >>> >>> m >> >>Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. >>Seems simple enough. >> >>George H. > >Some guy here once posted measured time constants of some film caps. >The numbers were in years, or possibly centuries.
If you have a charged cap that has a big negative temperature coefficient, when the temp increases C decreases, CV is conserved, so the voltage goes up. Stored energy increases. So does the charged cap have a higher specific heat than a discharged cap? -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Tuesday, August 2, 2016 at 11:44:00 AM UTC-4, John Larkin wrote:
> On Tue, 02 Aug 2016 08:29:10 -0700, John Larkin > <jjlarkin@highlandtechnology.com> wrote: > > >On Tue, 2 Aug 2016 06:55:52 -0700 (PDT), George Herold > ><gherold@teachspin.com> wrote: > > > >>On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote: > >>> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: > >>> > Greetings, > >>> > > >>> > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... > >>> > > >>> > > >>> > http://datasheets.avx.com/cb-petht.pdf > >>> > > >>> > Can someone interpret? > >>> > > >>> > > >>> > Thanks, > >>> > Bob > >>> > N9NEO > >>> > >>> I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? > >>> > >>> m > >> > >>Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. > >>Seems simple enough. > >> > >>George H. > > > >Some guy here once posted measured time constants of some film caps. > >The numbers were in years, or possibly centuries. > > If you have a charged cap that has a big negative temperature > coefficient, when the temp increases C decreases, CV is conserved, so > the voltage goes up. Stored energy increases. > > So does the charged cap have a higher specific heat than a discharged > cap?
Hmm, does the Q*V energy couple to the temperature of the cap? Where does the energy come from? A neg. TC means the cap expands as it warms up... pulling the "plates" apart. I guess that has to come from the thermal energy... I was going to say, "No, specific heat is the same". But I've talked myself into yes. George H.
> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
John Larkin <jjlarkin@highlandtechnology.com> wrote:
> On Tue, 02 Aug 2016 08:29:10 -0700, John Larkin > <jjlarkin@highlandtechnology.com> wrote: > >>On Tue, 2 Aug 2016 06:55:52 -0700 (PDT), George Herold >><gherold@teachspin.com> wrote: >> >>>On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote: >>>> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: >>>> > Greetings, >>>> > >>>> > I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... >>>> > >>>> > >>>> > http://datasheets.avx.com/cb-petht.pdf >>>> > >>>> > Can someone interpret? >>>> > >>>> > >>>> > Thanks, >>>> > Bob >>>> > N9NEO >>>> >>>> I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? >>>> >>>> m >>> >>>Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. >>>Seems simple enough. >>> >>>George H. >> >>Some guy here once posted measured time constants of some film caps. >>The numbers were in years, or possibly centuries. > > If you have a charged cap that has a big negative temperature > coefficient, when the temp increases C decreases, CV is conserved, so > the voltage goes up. Stored energy increases.
It may be wrong to assume CV is conserved. There's quite a bit of literature on dielectric constant changes for various films over temperature ranges, but I haven't come across any that explain what happens to a stored charge during a change in temperature or dielectric constant. It may be lost as heat. Another fun question is does storing a charge affect the melting/glass/transition temperatures of dielectrics? Anybody here ever make a parrafin wax electret? I havan't, yet.
On Tue, 2 Aug 2016 06:38:14 -0700 (PDT), the renowned Yzordderrex
<powersupplyguy@netzero.net> wrote:

>Greetings, > >I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... > > >http://datasheets.avx.com/cb-petht.pdf > >Can someone interpret? > > >Thanks, >Bob >N9NEO
It says IR C > 400 seconds. That means that the insulation resistance times the capacitance (the self-discharge RC time constant) is > 400 seconds. So if your cap is 2.2uF then R > 181M ohms. In practice this kind of spec tends to be an artificially 'bad' limit set by the maximum test time they want to allot, test equipment leakage or something like that. The insulation resistance of a film cap (that hasn't been damaged or contaminated- like a reworked SMT film cap that has split apart and got moisture inside!) is likely much higher than the guaranteed spec- by orders of magnitude- probably
>>10G.
--sp -- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
On 8/2/2016 2:47 PM, Cydrome Leader wrote:
> John Larkin <jjlarkin@highlandtechnology.com> wrote: >> On Tue, 02 Aug 2016 08:29:10 -0700, John Larkin >> <jjlarkin@highlandtechnology.com> wrote: >> >>> On Tue, 2 Aug 2016 06:55:52 -0700 (PDT), George Herold >>> <gherold@teachspin.com> wrote: >>> >>>> On Tuesday, August 2, 2016 at 9:49:25 AM UTC-4, mako...@yahoo.com wrote: >>>>> On Tuesday, August 2, 2016 at 9:38:26 AM UTC-4, Yzordderrex wrote: >>>>>> Greetings, >>>>>> >>>>>> I am having difficulty interpreting insulation resistance spec. It is on first page. IR C >400 sec. ..... >>>>>> >>>>>> >>>>>> http://datasheets.avx.com/cb-petht.pdf >>>>>> >>>>>> Can someone interpret? >>>>>> >>>>>> >>>>>> Thanks, >>>>>> Bob >>>>>> N9NEO >>>>> >>>>> I would "guess" there is a typo and it should say TC (time constant) > 400 seconds? >>>>> >>>>> m >>>> >>>> Hmm... I would just read it as IR (insulation resistance) * C > 400 seconds. >>>> Seems simple enough. >>>> >>>> George H. >>> >>> Some guy here once posted measured time constants of some film caps. >>> The numbers were in years, or possibly centuries. >> >> If you have a charged cap that has a big negative temperature >> coefficient, when the temp increases C decreases, CV is conserved, so >> the voltage goes up. Stored energy increases. > > It may be wrong to assume CV is conserved. There's quite a bit of > literature on dielectric constant changes for various films over > temperature ranges, but I haven't come across any that explain what > happens to a stored charge during a change in temperature or dielectric > constant. It may be lost as heat. Another fun question is does storing a > charge affect the melting/glass/transition temperatures of dielectrics? > > Anybody here ever make a parrafin wax electret? I havan't, yet.
I'm pretty sure charge is conserved... it would be a pretty strange world if it weren't and so far, I've not see any physicist say it isn't conserved. So CV is constant. But let's consider another example. A capacitor is made with some dielectric with a large relative permittivity, say 4, giving a capacitance of C. Charge the capacitor up to voltage V. So the charge is CV and the energy is CV^2. Now, remove the dielectric. The charge is still CV but it is also C'V' where C' is C/4, so V' must be V*4. The energy is now 4*CV^2. Clearly if this is correct, energy was added by removing the dielectric. Since the only source of energy was force times distance, there must be a force exerted on the dielectric as it is removed. D delta E = Integral F(x) dx 0 -- Rick C