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Capacitor soakage

Started by Prof78 February 6, 2017
Looking for advice/experience on measurement of capacitor soakage. Would like to determine an approximate equivalent circuit for a 1uF polypropylene capacitor at very low frequency/time intervals of tens of seconds.

Scott Hamilton.
On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78
<scott.hamilton@manchester.ac.uk> wrote:

>Looking for advice/experience on measurement of capacitor soakage. Would like to determine an approximate equivalent circuit for a 1uF polypropylene capacitor at very low frequency/time intervals of tens of seconds. > >Scott Hamilton.
Did you read Bob Pease's article? A bunch of RC's in parallel with an ideal cap should do it. --sp -- Best regards, Spehro Pefhany
Prof78 wrote:
> > > Looking for advice/experience on measurement of capacitor soakage. > Would like to determine an approximate equivalent circuit for a 1uF > polypropylene capacitor at very low frequency/time intervals of tens > of seconds. > >
** Surely you know polyprop caps have very low DA (dielectric absorption) ? The actual performance of examples will vary from one to another, from batch to batch and even with the cap's particular history. Mad to assume they are all the same. Leakage is just as variable too. Try polystyrene is you want to minimise that. ..... Phil
On Monday, 6 February 2017 14:51:38 UTC, Phil Allison  wrote:
> Prof78 wrote: > > > > > > Looking for advice/experience on measurement of capacitor soakage. > > Would like to determine an approximate equivalent circuit for a 1uF > > polypropylene capacitor at very low frequency/time intervals of tens > > of seconds. > > > > > > ** Surely you know polyprop caps have very low DA (dielectric absorption) ? > > The actual performance of examples will vary from one to another, from batch to batch and even with the cap's particular history. > > Mad to assume they are all the same. > > Leakage is just as variable too. > > Try polystyrene is you want to minimise that. > > > > ..... Phil
Yes I am aware of the variability but this is an extreme application where individual systems are hand adjusted to get the desired response.
On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany  wrote:
> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 > <scott.hamilton@manchester.ac.uk> wrote: > > >Looking for advice/experience on measurement of capacitor soakage. Would like to determine an approximate equivalent circuit for a 1uF polypropylene capacitor at very low frequency/time intervals of tens of seconds. > > > >Scott Hamilton. > > > Did you read Bob Pease's article? A bunch of RC's in parallel with an > ideal cap should do it. > > --sp > > > -- > Best regards, > Spehro Pefhany
Yes I have read the articles by Bob Pease but I need to be able to measure and determine the equivalent circuit for a given capacitor so that compensation can be applied. Each unit is hand adjusted. Scott Hamilton.
On 02/08/2017 11:43 AM, Prof78 wrote:
> On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany wrote: >> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 >> <scott.hamilton@manchester.ac.uk> wrote: >> >>> Looking for advice/experience on measurement of capacitor >>> soakage. Would like to determine an approximate equivalent >>> circuit for a 1uF polypropylene capacitor at very low >>> frequency/time intervals of tens of seconds. >>> >>> Scott Hamilton. >> >> >> Did you read Bob Pease's article? A bunch of RC's in parallel with >> an ideal cap should do it. >> >> --sp >> >> >> -- Best regards, Spehro Pefhany > > Yes I have read the articles by Bob Pease but I need to be able to > measure and determine the equivalent circuit for a given capacitor so > that compensation can be applied. Each unit is hand adjusted.
Yikes, that sounds like nailing jello to a tree. Do you have any reason to suppose that all the internal time constants would be temperature-independent? Cuz otherwise that's a nasty calibration table to create. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Wednesday, February 8, 2017 at 11:59:10 AM UTC-5, Phil Hobbs wrote:
> On 02/08/2017 11:43 AM, Prof78 wrote: > > On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany wrote: > >> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 > >> <scott.hamilton@manchester.ac.uk> wrote: > >> > >>> Looking for advice/experience on measurement of capacitor > >>> soakage. Would like to determine an approximate equivalent > >>> circuit for a 1uF polypropylene capacitor at very low > >>> frequency/time intervals of tens of seconds. > >>> > >>> Scott Hamilton. > >> > >> > >> Did you read Bob Pease's article? A bunch of RC's in parallel with > >> an ideal cap should do it. > >> > >> --sp > >> > >> > >> -- Best regards, Spehro Pefhany > > > > Yes I have read the articles by Bob Pease but I need to be able to > > measure and determine the equivalent circuit for a given capacitor so > > that compensation can be applied. Each unit is hand adjusted. > > Yikes, that sounds like nailing jello to a tree. Do you have any reason > to suppose that all the internal time constants would be > temperature-independent? Cuz otherwise that's a nasty calibration table > to create.
Is there any reason to believe it will be linear with the voltage step? (Sounds like a research project.) I thought I read once that teflon caps had low soakage. Maybe they are better than polypropylene? George h.
> > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
On 02/08/2017 01:30 PM, George Herold wrote:
> On Wednesday, February 8, 2017 at 11:59:10 AM UTC-5, Phil Hobbs wrote: >> On 02/08/2017 11:43 AM, Prof78 wrote: >>> On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany wrote: >>>> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 >>>> <scott.hamilton@manchester.ac.uk> wrote: >>>> >>>>> Looking for advice/experience on measurement of capacitor >>>>> soakage. Would like to determine an approximate equivalent >>>>> circuit for a 1uF polypropylene capacitor at very low >>>>> frequency/time intervals of tens of seconds. >>>>> >>>>> Scott Hamilton. >>>> >>>> >>>> Did you read Bob Pease's article? A bunch of RC's in parallel with >>>> an ideal cap should do it. >>>> >>>> --sp >>>> >>>> >>>> -- Best regards, Spehro Pefhany >>> >>> Yes I have read the articles by Bob Pease but I need to be able to >>> measure and determine the equivalent circuit for a given capacitor so >>> that compensation can be applied. Each unit is hand adjusted. >> >> Yikes, that sounds like nailing jello to a tree. Do you have any reason >> to suppose that all the internal time constants would be >> temperature-independent? Cuz otherwise that's a nasty calibration table >> to create. > > Is there any reason to believe it will be linear with the voltage step? > (Sounds like a research project.) > > I thought I read once that teflon caps had low soakage. Maybe they > are better than polypropylene? > > George h.
Film caps are all pretty good--none of the common polymers is ferroelectric, so they don't saturate like titanates and so forth. If I were doing it, I'd probably use a dynamic signal analyzer to measure the transfer function of an RC lowpass and let it run over the weekend. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Wed, 8 Feb 2017 13:39:32 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 02/08/2017 01:30 PM, George Herold wrote: >> On Wednesday, February 8, 2017 at 11:59:10 AM UTC-5, Phil Hobbs wrote: >>> On 02/08/2017 11:43 AM, Prof78 wrote: >>>> On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany wrote: >>>>> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 >>>>> <scott.hamilton@manchester.ac.uk> wrote: >>>>> >>>>>> Looking for advice/experience on measurement of capacitor >>>>>> soakage. Would like to determine an approximate equivalent >>>>>> circuit for a 1uF polypropylene capacitor at very low >>>>>> frequency/time intervals of tens of seconds. >>>>>> >>>>>> Scott Hamilton. >>>>> >>>>> >>>>> Did you read Bob Pease's article? A bunch of RC's in parallel with >>>>> an ideal cap should do it. >>>>> >>>>> --sp >>>>> >>>>> >>>>> -- Best regards, Spehro Pefhany >>>> >>>> Yes I have read the articles by Bob Pease but I need to be able to >>>> measure and determine the equivalent circuit for a given capacitor so >>>> that compensation can be applied. Each unit is hand adjusted. >>> >>> Yikes, that sounds like nailing jello to a tree. Do you have any reason >>> to suppose that all the internal time constants would be >>> temperature-independent? Cuz otherwise that's a nasty calibration table >>> to create. >> >> Is there any reason to believe it will be linear with the voltage step? >> (Sounds like a research project.) >> >> I thought I read once that teflon caps had low soakage. Maybe they >> are better than polypropylene? >> >> George h. > >Film caps are all pretty good--none of the common polymers is >ferroelectric, so they don't saturate like titanates and so forth. > >If I were doing it, I'd probably use a dynamic signal analyzer to >measure the transfer function of an RC lowpass and let it run over the >weekend. > >Cheers > >Phil Hobbs
I'd time-domain it. Charge overnight, short briefly, log the open-circuit voltage for a day or so. You'd need a low-bias-current DVM or follower opamp. There could be a huge range of internal tau's. Someone here once posted long-term (months and years) leakage of some charged film caps. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 02/08/2017 03:38 PM, John Larkin wrote:
> On Wed, 8 Feb 2017 13:39:32 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 02/08/2017 01:30 PM, George Herold wrote: >>> On Wednesday, February 8, 2017 at 11:59:10 AM UTC-5, Phil Hobbs wrote: >>>> On 02/08/2017 11:43 AM, Prof78 wrote: >>>>> On Monday, 6 February 2017 13:57:52 UTC, Spehro Pefhany wrote: >>>>>> On Mon, 6 Feb 2017 05:31:04 -0800 (PST), the renowned Prof78 >>>>>> <scott.hamilton@manchester.ac.uk> wrote: >>>>>> >>>>>>> Looking for advice/experience on measurement of capacitor >>>>>>> soakage. Would like to determine an approximate equivalent >>>>>>> circuit for a 1uF polypropylene capacitor at very low >>>>>>> frequency/time intervals of tens of seconds. >>>>>>> >>>>>>> Scott Hamilton. >>>>>> >>>>>> >>>>>> Did you read Bob Pease's article? A bunch of RC's in parallel with >>>>>> an ideal cap should do it. >>>>>> >>>>>> --sp >>>>>> >>>>>> >>>>>> -- Best regards, Spehro Pefhany >>>>> >>>>> Yes I have read the articles by Bob Pease but I need to be able to >>>>> measure and determine the equivalent circuit for a given capacitor so >>>>> that compensation can be applied. Each unit is hand adjusted. >>>> >>>> Yikes, that sounds like nailing jello to a tree. Do you have any reason >>>> to suppose that all the internal time constants would be >>>> temperature-independent? Cuz otherwise that's a nasty calibration table >>>> to create. >>> >>> Is there any reason to believe it will be linear with the voltage step? >>> (Sounds like a research project.) >>> >>> I thought I read once that teflon caps had low soakage. Maybe they >>> are better than polypropylene? >>> >>> George h. >> >> Film caps are all pretty good--none of the common polymers is >> ferroelectric, so they don't saturate like titanates and so forth. >> >> If I were doing it, I'd probably use a dynamic signal analyzer to >> measure the transfer function of an RC lowpass and let it run over the >> weekend. >> >> Cheers >> >> Phil Hobbs > > > I'd time-domain it. Charge overnight, short briefly, log the > open-circuit voltage for a day or so. You'd need a low-bias-current > DVM or follower opamp. > > There could be a huge range of internal tau's. > > Someone here once posted long-term (months and years) leakage of some > charged film caps. > >
I'd sort of expect leakage and tempco to make the analysis harder that way, though. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net