Just charge them up with your DC hipot tester to peak voltage when in the off state.if the circuit and your hipot tester allow. May work in some circumstances with simple front ends.
Dan From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Monday, October 17, 2022 10:12 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Assess risk of electric shock from charged capacitors I'm curious as to the rationale behind that. It should be obvious that the power was turned off at the appropriate time. That would be demonstrated using an o'scope, just as in the hit or miss method. What's different? Ken Javor Phone: (256) 650-5261 _____ From: "doug...@gmail.com" <doug...@gmail.com> Reply-To: "doug...@gmail.com" <doug...@gmail.com> Date: Mon, 17 Oct 2022 17:37:21 -0600 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Assess risk of electric shock from charged capacitors Ken, Yes, but I have had certification engineers hesitate or disallow using any home-brew solid state circuits to control safety testing. -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> (UTC -06:00) Mountain Time (US-MDT) On Mon, Oct 17, 2022 at 1:18 PM Ken Javor <ken.ja...@emccompliance.com> wrote: A simple circuit can provide disconnect at the peak of the ac waveform. Ken Javor Phone: (256) 650-5261 _____ From: "doug...@gmail.com <http://doug...@gmail.com> " <doug...@gmail.com <http://doug...@gmail.com> > Reply-To: "doug...@gmail.com <http://doug...@gmail.com> " <doug...@gmail.com <http://doug...@gmail.com> > Date: Mon, 17 Oct 2022 13:08:17 -0600 To: <EMC-PSTC@LISTSERV.IEEE.ORG <http://EMC-PSTC@LISTSERV.IEEE.ORG> > Subject: Re: [PSES] Assess risk of electric shock from charged capacitors On the question of probe resistance, I always recommend 100:1 probes which will have a negligible effect on overall timing. Additionally, it may be necessary to perform the test a number times to ensure the disconnect occurs at the peak of the sine wave. For me, experience has shown this may take up to 10x attempts. -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com <http://doug...@gmail.com> LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> (UTC -06:00) Mountain Time (US-MDT) On Mon, Oct 17, 2022 at 11:32 AM Richard Nute <ri...@ieee.org <http://ri...@ieee.org> > wrote: Hi Scott: Many dual channel scopes (whether digital or analog) include an "add" function for the two channels. One channel must be inverted to measure the charged capacitance. The resistance of the two probes must be accounted for in the capacitance discharge time. (The same - for only one probe -- is true for the scheme using an isolating transformer.) You should get the same results for both methods. Best regards, Rich IEEE Life Fellow IEEE Medal for Environmental and Safety Technologies From: Scott Xe <scott...@gmail.com <http://scott...@gmail.com> > Sent: Monday, October 17, 2022 8:18 AM To: EMC-PSTC@LISTSERV.IEEE.ORG <http://EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Assess risk of electric shock from charged capacitors In order to judge if there is no risk of electric shock from charged capacitors, it is required to measure the voltage across L and N of mains plug after the removal of power input. To avoid grounding loop between test equipment and the unit under test, an isolating transformer is strongly recommended. I have learnt another way by using Add Function and two hot probes of a dual channel DSO. Can someone advise which way is more common in safety conformity test. Especially the latter one, I have not tried it yet before and appreciate any notes I must take in the measurement. 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