Forums

configure esr for noncharted caps

Started by medusa March 25, 2016
Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets?
On Fri, 25 Mar 2016 05:46:00 -0700 (PDT), medusa
<medusa569@verizon.net> wrote:

>Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets?
Is there a simple way to do something that wasn't easy in the first place? No. RL
On Friday, 25 March 2016 12:46:06 UTC, medusa  wrote:
> Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets?
Approach 1: look up a table of typical values. Hit & miss, inevitably. Approach 2: use a bridge. Simple, yes. Quick, not really. Approach 3: buy an ESR meter. Cheapest I've seen are &#2013266083;12 on ebay, but their lower R limit is basic & only useful for electrolytics. NT
medusa wrote...
> > Is there a simple way without oscilloscope to > estimate the expected esr of caps that are not > on the charts and don't have access to data sheets?
Yes. Start with a power resistor chosen to place a substantial current load on the charged capacitor. Switch the bottom (ground) end of the resistor with a power MOSFET, drive the MOSFET from a pulse generator. Use your scope in its ac-coupled mode to see the step changes in voltage vs load on-off across the capacitor terminals. To keep it all honest, move the probe from the top to the bottom of the cap to verify the voltage step change, as opposed to ground-wiring voltage drops. This will work, but I prefer an HP LCR meter with variable test frequency and milli-ohm sensitivity. Get them used on eBay. I like the hp 4192A. -- Thanks, - Win
On Fri, 25 Mar 2016 05:46:00 -0700 (PDT), medusa
<medusa569@verizon.net> wrote:

>Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets?
What equipment do you have? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 25 Mar 2016 10:15:26 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

>medusa wrote... >> >> Is there a simple way without oscilloscope to >> estimate the expected esr of caps that are not >> on the charts and don't have access to data sheets? > > Yes. > > Start with a power resistor chosen to place a > substantial current load on the charged capacitor. > Switch the bottom (ground) end of the resistor > with a power MOSFET, drive the MOSFET from a pulse > generator. Use your scope in its ac-coupled mode > to see the step changes in voltage vs load on-off > across the capacitor terminals. To keep it all > honest, move the probe from the top to the bottom > of the cap to verify the voltage step change, as > opposed to ground-wiring voltage drops. > > This will work, but I prefer an HP LCR meter with > variable test frequency and milli-ohm sensitivity. > Get them used on eBay. I like the hp 4192A.
He doesn't have an oscilloscope! Here's a 50 ohm function generator making a square wave into an electrolytic cap. You can see C, ESR, and ESL in the waveform. https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Polymer_ESR.JPG Time domain rules! -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 3/25/2016 12:50 PM, John Larkin wrote:
> On 25 Mar 2016 10:15:26 -0700, Winfield Hill > <hill@rowland.harvard.edu> wrote: > >> medusa wrote... >>> >>> Is there a simple way without oscilloscope to >>> estimate the expected esr of caps that are not >>> on the charts and don't have access to data sheets? >> >> Yes. >> >> Start with a power resistor chosen to place a >> substantial current load on the charged capacitor. >> Switch the bottom (ground) end of the resistor >> with a power MOSFET, drive the MOSFET from a pulse >> generator. Use your scope in its ac-coupled mode >> to see the step changes in voltage vs load on-off >> across the capacitor terminals. To keep it all >> honest, move the probe from the top to the bottom >> of the cap to verify the voltage step change, as >> opposed to ground-wiring voltage drops. >> >> This will work, but I prefer an HP LCR meter with >> variable test frequency and milli-ohm sensitivity. >> Get them used on eBay. I like the hp 4192A. > > He doesn't have an oscilloscope! > > Here's a 50 ohm function generator making a square wave into an > electrolytic cap. You can see C, ESR, and ESL in the waveform. > > https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Polymer_ESR.JPG > > Time domain rules!
To quote JL: "He doesn't have an oscilloscope!"
On 3/25/2016 10:43 AM, John Larkin wrote:
> On Fri, 25 Mar 2016 05:46:00 -0700 (PDT), medusa > <medusa569@verizon.net> wrote: > >> Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets? > > What equipment do you have? > >
http://www.daqarta.com/dw_0o0z.htm
On Fri, 25 Mar 2016 13:42:38 -0700, mike <ham789@netzero.net> wrote:

>On 3/25/2016 10:43 AM, John Larkin wrote: >> On Fri, 25 Mar 2016 05:46:00 -0700 (PDT), medusa >> <medusa569@verizon.net> wrote: >> >>> Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets? >> >> What equipment do you have? >> >> >http://www.daqarta.com/dw_0o0z.htm
My square wave trick might work. Or do it in the frequency domain: inject a sine wave current, sweep the frequency, measure the terminal voltage. It should be a sort of bathtub curve, with the low, flat part defining ESR. But they have an ESR app: http://www.daqarta.com/dw_0o0z.htm -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Fri, 25 Mar 2016 14:31:15 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Fri, 25 Mar 2016 13:42:38 -0700, mike <ham789@netzero.net> wrote: > >>On 3/25/2016 10:43 AM, John Larkin wrote: >>> On Fri, 25 Mar 2016 05:46:00 -0700 (PDT), medusa >>> <medusa569@verizon.net> wrote: >>> >>>> Is there a simple way without oscilloscope to estimate the expected esr of caps that are not on the charts and don't have access to data sheets? >>> >>> What equipment do you have? >>> >>> >>http://www.daqarta.com/dw_0o0z.htm > >My square wave trick might work. Or do it in the frequency domain: >inject a sine wave current, sweep the frequency, measure the terminal >voltage. It should be a sort of bathtub curve, with the low, flat part >defining ESR. > >But they have an ESR app: > >http://www.daqarta.com/dw_0o0z.htm
Is that the same Robert Macy that used to post here? Cheers