Re: Resistors pulse loading capabilities
Massimo, Just to underscore what others have stated, long ago in one of the resistor mfr's catalogues, there was a discussion of this topic. Essentially, do not violate the DC wattage rating of the resistor based on a 1 second time period. As an example, a 1W, 1 Ohm, carbon composition resistor should be able to handle a. 1A (or 1V potential) continuously, b. 2A (or 2V potential) at 50% duty cycle, i.e. 1/2 second duration, c. 4A at 25% duty cycle, i.e. 1/4 second duration, etc ... all the way up to the maximum voltage rating of the resistor. For a 600V rated resistor, this would mean the maximum pulse allowed would be 600V peak for less than or equal to 1/600th second or 1.6 milliseconds. This particular conclusion I have doubts about. I explain below. Fusing characteristics of wires is non-linear and therefore for large currents through a resistor (I don't know what that might be), I doubt the above. But for low currents, let's say less than 10 times the current rating of the resistor for the sake of argument (in the case above, that would mean anything less than 10 amps), I think that's acceptable. This is all spectulation and I am by no means an expert. But, if there is any question, please consult the mfr. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Resistors pulse loading capabilities
-Original Message- From: John Barnes [mailto:jrbar...@iglou.com] Sent: Tuesday, February 19, 2002 4:45 AM To: emc-p...@majordomo.ieee.org Subject: Re: Resistors pulse loading capabilities Massimo, All the tests that I've seen for evaluating the peak-pulse-power handling capabilities of resistors are based on charging a bank of capacitors to a high voltage, then applying this energy (E = 1/2 * c * V * V) to the part/equipment-under-test through a low-resistance low-inductance switch or relay. You need to be very careful running these tests, because there is enough energy involved to kill you! For the Keytek surge generator that I used to run IBM Lightning Surge Susceptibility tests on network adapter cards, this came to something like 4 joules at 800 volts, with the tester rated to deliver up to 200 amps maximum. That tester required you to toggle two widely-spaced switches to trigger a discharge, to make sure that you had both hands on the tester. I always triple-checked my test setup, then had another experienced engineer double-check me, before I even plugged in the surge tester. I blew up quite a few components, and fried a few circuit boards, while developing/helping develop some 35 IBM and Lexmark networking/digital-office products from 1990 through January 2002. NOTE: You also want to put a direct short across the capacitors when the tester is not in use. Dielectric absorbtion stores some energy in the dielectric of a capacitors as a physical displacement of the atoms. This can take seconds to hours to relax, and as it does it induces a corresponding charge on the capacitors' plates. Without a bleeder resistor of some type across the capacitors, up to 10% or so of the initial charging voltage can appear on the capacitors after they have supposedly been discharged. This could give you a nasty, if non-fatal shock, next time you want to use the tester. As for help choosing the resistors for your circuit, check out The Resistor Handbook by Cletus J. Kaiser (98 pages, 1994, CJ Publishing, Olathe, Kansas, ISBN 0-9628525-1-1). This is the best single source I've found for information on resistors. On page 3, under the subheading One Short Pulse it says: The theory of pulse handling depends on the pulse width. One short pulse of 100 milliseconds or less is assumed to never havetime enough to do more than heat the element. Therefore the calculation is based on the total mass of the element (wire) being heated to the maximum internal hot-spot temperature. As Bob Wilson said, this will depend on the overall type of resistor, and on the specific details of its construction (i.e. manufacturer/ series). You need to consider the bulk sections of the resistor, which have relatively-uniform construction, and the interfaces between them. So I would expect bulk-metal resistors, such as those made by Vishay, to have the highest peak-power/rated-power capability because they are essentially one piece of metal. From there I would look at: 1. Carbon-composition resistors. 2. Wirewound resistors. 3. Untrimmed metal-film resistors. 4. Untrimmed carbon-film resistors. 5. Untrimmed cermet resistors. 6. Trimmed metal-film resistors. 7. Trimmed carbon-film resistors. 8. Trimmed cermet resistors. The untrimmed film resistors have rather sloppy tolerances, on the order of +/-20% or so, but have much higher pulse-power handling capability than their trimmed brethren. (We got bitten by this, when purchasing had trouble getting the part we had specified for a Token-Ring card, and substituted a part that the salesman said was even better than the one we wanted.) If you must use a trimmed resistor, because of tolerances, abrasive trimming would probably be better than laser trimming, because it makes a smoother cut and leaves less debris. I found it very educational to look at resistors under a microscope (about 10-30x magnification sufficed), both before and after running the Lightning Surge Susceptibility test. The failed resistors looked like they had been machine-gunned, with a vertical line of pits across the surface of the resistor from the corner of the L (left by trimming) to the edge of the resistor. John Barnes dBi Corporation --- Let me add one more type of resistor, right at the top of your list. I have used silicon carbide resistors (made by Carborundum, then Ceseiwid, now the name has changed again) as pulse generator loads and source impedance adjustors. These resistors have the inductance of a similar sized piece of rod stock, and can handle tremendous short duration currents. They can function properly right up to the point of glowing. They withstand high voltages pretty well (best to choose a rod shape rather than a thick washer or hockey puck shape). These resistors withstand power only
Re: Resistors pulse loading capabilities
Massimo, All the tests that I've seen for evaluating the peak-pulse-power handling capabilities of resistors are based on charging a bank of capacitors to a high voltage, then applying this energy (E = 1/2 * c * V * V) to the part/equipment-under-test through a low-resistance low-inductance switch or relay. You need to be very careful running these tests, because there is enough energy involved to kill you! For the Keytek surge generator that I used to run IBM Lightning Surge Susceptibility tests on network adapter cards, this came to something like 4 joules at 800 volts, with the tester rated to deliver up to 200 amps maximum. That tester required you to toggle two widely-spaced switches to trigger a discharge, to make sure that you had both hands on the tester. I always triple-checked my test setup, then had another experienced engineer double-check me, before I even plugged in the surge tester. I blew up quite a few components, and fried a few circuit boards, while developing/helping develop some 35 IBM and Lexmark networking/digital-office products from 1990 through January 2002. NOTE: You also want to put a direct short across the capacitors when the tester is not in use. Dielectric absorbtion stores some energy in the dielectric of a capacitors as a physical displacement of the atoms. This can take seconds to hours to relax, and as it does it induces a corresponding charge on the capacitors' plates. Without a bleeder resistor of some type across the capacitors, up to 10% or so of the initial charging voltage can appear on the capacitors after they have supposedly been discharged. This could give you a nasty, if non-fatal shock, next time you want to use the tester. As for help choosing the resistors for your circuit, check out The Resistor Handbook by Cletus J. Kaiser (98 pages, 1994, CJ Publishing, Olathe, Kansas, ISBN 0-9628525-1-1). This is the best single source I've found for information on resistors. On page 3, under the subheading One Short Pulse it says: The theory of pulse handling depends on the pulse width. One short pulse of 100 milliseconds or less is assumed to never havetime enough to do more than heat the element. Therefore the calculation is based on the total mass of the element (wire) being heated to the maximum internal hot-spot temperature. As Bob Wilson said, this will depend on the overall type of resistor, and on the specific details of its construction (i.e. manufacturer/ series). You need to consider the bulk sections of the resistor, which have relatively-uniform construction, and the interfaces between them. So I would expect bulk-metal resistors, such as those made by Vishay, to have the highest peak-power/rated-power capability because they are essentially one piece of metal. From there I would look at: 1. Carbon-composition resistors. 2. Wirewound resistors. 3. Untrimmed metal-film resistors. 4. Untrimmed carbon-film resistors. 5. Untrimmed cermet resistors. 6. Trimmed metal-film resistors. 7. Trimmed carbon-film resistors. 8. Trimmed cermet resistors. The untrimmed film resistors have rather sloppy tolerances, on the order of +/-20% or so, but have much higher pulse-power handling capability than their trimmed brethren. (We got bitten by this, when purchasing had trouble getting the part we had specified for a Token-Ring card, and substituted a part that the salesman said was even better than the one we wanted.) If you must use a trimmed resistor, because of tolerances, abrasive trimming would probably be better than laser trimming, because it makes a smoother cut and leaves less debris. I found it very educational to look at resistors under a microscope (about 10-30x magnification sufficed), both before and after running the Lightning Surge Susceptibility test. The failed resistors looked like they had been machine-gunned, with a vertical line of pits across the surface of the resistor from the corner of the L (left by trimming) to the edge of the resistor. John Barnes dBi Corporation --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Resistors pulse loading capabilities
I suspect that this will depend very strongly on the characteristics of specific type of resistor. Further, there will undoubtedly be very significant differences from manufacturer to manufacturer, in the ability to absorb stresses well beyond normal design intent. I think it would be rather hard (or even perhaps impossible) to make generalizations that would apply to, for example, all 1 Watt resistors. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Massimo Polignano [mailto:massimo.polign...@esaote.com] Sent: February 18, 2002 6:03 AM To: emc-p...@majordomo.ieee.org Subject: Resistors pulse loading capabilities Does anybody out of there know what are the methods to evaluate resistors pulse loading capabilities (maximum peak pulse voltage without failing to open circuit)? Is there any standard models? This could be very useful to design the power supply circuit parts involved in a surge immunity test. Thanks in advance. m.p. - ESAOTE S.p.A. Massimo Polignano Research Product DevelopmentDesign Quality Control Mngr Via di Caciolle,15tel:+39.055.4229402 I- 50127 Florence fax:+39.055.4223305 e-mail: massimo.polign...@esaote.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Resistors pulse loading capabilities
Hi Massimo, Try http://www.vtm.co.uk/. They had a good calculation method in the printed version of their catalog which does not seem to be available on the website ( I haven't looked very hard for it). It worked well for sizing in-rush limiting resistors. Regards - Chris -Original Message- From: Massimo Polignano [SMTP:massimo.polign...@esaote.com] Sent: Monday, February 18, 2002 2:03 PM To: emc-p...@majordomo.ieee.org Subject:Resistors pulse loading capabilities Does anybody out of there know what are the methods to evaluate resistors pulse loading capabilities (maximum peak pulse voltage without failing to open circuit)? Is there any standard models? This could be very useful to design the power supply circuit parts involved in a surge immunity test. Thanks in advance. m.p. - ESAOTE S.p.A. Massimo Polignano Research Product DevelopmentDesign Quality Control Mngr Via di Caciolle,15tel:+39.055.4229402 I- 50127 Florence fax:+39.055.4223305 e-mail: massimo.polign...@esaote.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list This e-mail has been scanned for all viruses by Star Internet. The service is powered by MessageLabs. For more information on a proactive anti-virus service working around the clock, around the globe, visit: http://www.star.net.uk This e-mail has been scanned for all viruses by Star Internet. The service is powered by MessageLabs. For more information on a proactive anti-virus service working around the clock, around the globe, visit: http://www.star.net.uk --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Resistors pulse loading capabilities
I read in !emc-pstc that Massimo Polignano massimo.polign...@esaote.com wrote (in OF78266151.726D3F50-ONC1256B64 .004c7...@esaote.com) about 'Resistors pulse loading capabilities', on Mon, 18 Feb 2002: Does anybody out of there know what are the methods to evaluate resistors pulse loading capabilities (maximum peak pulse voltage without failing to open circuit)? Is there any standard models? This could be very useful to design the power supply circuit parts involved in a surge immunity test. Try IEC60115 (a multi-part standard) and IEC/TR60440. Brief details are available at http://www.iec.ch The specification sheets for metal glaze resistors, such as Philips VR25 and VR37, may be informative. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. PLEASE do NOT copy news posts to me by E-MAIL! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
