It depend very much of the heat properties of the resistor. I would go for a large resistor, with lots of thermal buffer. The power rating would be 500 W x 50E-6 = 2.5 mW as that is the total power per second (assuming < 1 pulse /sec). (= continuous power x pulse width) which is way less then any resistor available. All will do for that. But the problem is that in small resistors, the resistor coating will evaporate in 50 microseconds. That is why it needs to be a bit bulky. I guess that most metal film resistors of 1 watt and larger are big enough. I would exclude SMD's.
Gert Gremmen Ce-test Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens John Woodgate Verzonden: donderdag 29 oktober 2009 18:32 Aan: emc-p...@ieee.org Onderwerp: Re: Converting energy to power rating for surge transient In message <541403.70322...@web52201.mail.re2.yahoo.com>, dated Thu, 29 Oct 2009, Dave Wilson <davewilson...@yahoo.com> writes: > >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? It's not a matter of power rating. You need a resistor that will withstand the thermal shock of 1 A being applied over 1.2 μs, in addition to the 500 V applied. It also needs to have negligible inductance. There are companies that make resistors specially for this sort of application. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK Help stamp out intolerance! - 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>
