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Re: Capacitor soakage

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On 02/09/2017 11:30 AM, John Larkin wrote:
> On Wed, 8 Feb 2017 16:11:08 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> 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
>
> Leakage is just one more component of the circuit model, the 1st order
> time constant. But a good film cap apparently leaks a fraction of a
> per cent per year.
>
> Capacitance tempco will change the voltage, so I guess it should be
> tested at constant temperature. But then the OP will have to run the
> actual thing at a constant temp if he expects to compensate to the
> measured accuracy.

I'd be very surprised if he didn't have to in any event, since the sorts 
of relaxation processes that give rise to soakage must have fairly 
dramatic temperature dependences.

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

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Capacitor soakage Prof78 <scott.hamilton@manchester.ac.uk> - 2017-02-06 05:31 -0800
  Re: Capacitor soakage Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-06 08:57 -0500
    Re: Capacitor soakage Prof78 <scott.hamilton@manchester.ac.uk> - 2017-02-08 08:43 -0800
      Re: Capacitor soakage Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 11:59 -0500
        Re: Capacitor soakage George Herold <gherold@teachspin.com> - 2017-02-08 10:30 -0800
          Re: Capacitor soakage Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 13:39 -0500
            Re: Capacitor soakage John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-08 12:38 -0800
              Re: Capacitor soakage Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 16:11 -0500
                Re: Capacitor soakage John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-09 08:30 -0800
                Re: Capacitor soakage Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:55 -0500
            Re: Capacitor soakage bill.sloman@ieee.org - 2017-02-08 14:53 -0800
              Re: Capacitor soakage Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-08 19:11 -0500
          Re: Capacitor soakage Frank Miles <fpm@u.washington.edu> - 2017-02-08 22:36 +0000
            Re: Capacitor soakage George Herold <gherold@teachspin.com> - 2017-02-08 17:48 -0800
              Re: Capacitor soakage John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-09 11:17 -0800
                Re: Capacitor soakage "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-09 16:46 -0600
                Re: Capacitor soakage krw@notreal.com - 2017-02-09 20:44 -0500
                Re: Capacitor soakage bill.sloman@ieee.org - 2017-02-09 19:15 -0800
                Re: Capacitor soakage John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-09 20:54 -0800
            Re: Capacitor soakage John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-09 11:16 -0800
              Re: Capacitor soakage George Herold <gherold@teachspin.com> - 2017-02-09 12:02 -0800
          Re: Capacitor soakage Robert Baer <robertbaer@localnet.com> - 2017-02-08 20:50 -0800
            Re: Capacitor soakage George Herold <gherold@teachspin.com> - 2017-02-09 06:36 -0800
      Re: Capacitor soakage Phil Allison <pallison49@gmail.com> - 2017-02-08 17:10 -0800
  Re: Capacitor soakage Phil Allison <pallison49@gmail.com> - 2017-02-06 06:51 -0800
    Re: Capacitor soakage Prof78 <scott.hamilton@manchester.ac.uk> - 2017-02-08 08:32 -0800
      Re: Capacitor soakage Tim Wescott <seemywebsite@myfooter.really> - 2017-02-08 17:48 -0600
      Re: Capacitor soakage "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-08 17:56 -0600

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