Mick, Mike et al,
I recommend resistors from HVR. They have “non-inductive” resistors and will help you decide what you need based on joule ratings instead of wattage ratings. Sometimes they have some stuff in stock and they can let you know. Often I end up putting their resistors in parallel or series to achieve the values I need based on what is in stock as I usually don’t have a week or more to wait. We have not had a single resistor failure and we use these all the time for external networks. http://www.hvrapc.com/products.asp Jim Jim Wiese Senior Compliance Engineer ADTRAN, Inc. 901 Explorer Blvd. Huntsville, AL 35806 256-963-8431 256-714-5882 (cell) 256-963-6218 (fax) jim.wi...@adtran.com ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Mick Maytum on Gmail Sent: Thursday, October 29, 2009 2:19 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Cc: Michael Hopkins Subject: Re: [PSES] Converting energy to power rating for surge transient I need to determine what power rating a resistor has to be to adequately dissipate 0.5J (a 1.2/50us surge of 500V from a 500 ohm source). Anyone have a conversion formula? Like Mike I'm puzzled by 0.5 J number as well. The Exponential Impulse waveforms Annex of the ATIS 0600338 Electrical Coordination of Primary and Secondary Surge Protection for Use in Telecommunications Circuits states the i^2*t of an exponentially decaying current impulse of amplitude I and 50% decay time Td is 0.72*I^2*Td. The energy in a resistance R will be R*0.72*I^2*Td. I assume you are trying to dimension the 500 ohm source resistor. A 500 ohm resistor with a 1 A peak impulse current decaying in 50 µs will have an energy dump of 500*1^2*50E-6 or 25 mJ. Although the peak VI power is 500 W the average power at one impulse per minute is only 0.4 mW (25 mJ/ 60s) - so John is right continuous power rating isn't important If you are using a 1.2/50-8/20 combination wave generator then the impulse waveshape with a 500 ohms load will be 1.2/50 (least with the generators Mike was associated with) I would look for some high voltage pulse resistors. For these sort of energy and voltage levels I would start with thick film versions. Composite carbon resistors do have good HV withstand (carbon film variants don't have good HV withstand), but for the long term other technologies are preferable. Mick Maytum UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>
