RE: Use of PCB Traces as Fuse and Voltage suppressor
I can't verify the part that after a wrench was dropped on the -48V bus bars, all the other equipment was blown, but I can throw a little light on this. The previous company I worked for made Telco rectifiers. Our largest system had an output of over half a megawatt (!) at -48V. The bus bars were not little 1 diameter rods, but laminated copper bars that were 6 x 4 in cross section. One customer was worried about what would happen when ol' Bubba dropped his wrench across the bars, and I had to prove that the bars would not tear themselves loose due to the repulsive force caused by peak short circuit current from the batteries being charged by the rectifier system. The current was not insubstantial: 100,000 Amps would flow for about 15mS before the fuse cleared. It was assumed that not only would Bubba's wrench vapourize, but so would Bubba. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Robert Macy [mailto:m...@california.com] Sent: February 25, 2002 10:34 PM To: Jim Bacher; ieee pstc list Subject: Re: Use of PCB Traces as Fuse and Voltage suppressor Jim, You touch on an important issue concerning a fuse - just how does it blow? Years ago I discovered by accident that fuses were designed with some remarkable properties, when we had to make our own transient generator to verify some telcom equipment's compliance to a BABT power supply transient spec. The BABT spec required that you simulate some very husky power transients. It was like a short occurs in adjacent electronics followed by the inductive kick. The -48 voltage would clamp to around 10 volts then pop up to over 300 volts capable of supplying 500A for something like more than 50mS. If you didn't design your protection properly you would have a lot of unintentional PCB trace fuses. [ Actually heard that the spec originated because a workman had dropped his wrench across the 1 inch diameter rods which supply the -48 to the telco building from the battery building. After the wrench evaporated, they found the whole room of equipment was blown, thus the spec. Somebody verify that? ] The simulator used 4 deep discharge current vehicle batteries supplying the telcom equipment through 50uH of inductance (that was cable on a spool). Parallel to that you used a starter solenoid to short out a fuse with a dead short. Amazingly the larger fuses never produced much kick back. They were designed to blow gently away. Tried all kinds. Most of the 8AG didn't do much, other types, nothing, even the 100 amp cartridge types, nothing, The absolute best was a 1A 8AG type. When that went, you'd get a flash of light, 300 volts trying to drive 500 amps into everything, and even the coil would jump up off the floor. Talk about PCB traces acting like fuses. Anyway, I learned a respect for people who design fuses to make them go away so gently when there is an incredible potential for some extremely high voltage transients. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: Jim Bacher jim.bac...@paxar.com To: 'Cortland Richmond' 72146@compuserve.com; Chris Maxwell chris.maxw...@nettest.com; ieee pstc list emc-p...@ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, February 25, 2002 3:04 PM Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor Long time ago we found that the traces worked well as fuses when the batteries were fully charged. However, when the batteries were mostly discharged, the PC Board traces did not work well as fuses. At lower battery charge levels, the traces became very hot and ignited the PC Board rather than opening the traces up. I therefore would recommend against using PC Board traces as fuses. Jim Jim Bacher, Senior Engineer Paxar Corp. e-mail: jim.bac...@paxar.com or j.bac...@ieee.org voice: 1-937-865-2020 fax: 1-937-865-2048 -Original Message- From: Cortland Richmond [mailto:72146@compuserve.com] Sent: Thursday, February 21, 2002 12:53 AM To: Chris Maxwell; ieee pstc list Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor When do you need a fuse? Level II is the only time you are allowed to lose functionality, and the requirement for THAT is, it can't catch fire or explode. I've seen trace fuses tried. The problem comes after the trace blows. You are at the mercy of your board shop, and if you use a number of them, results might not be all that repeatable. AS i said earlier, I've had a board catch fire in my hand (though not as a result of stress, but a solder splash). It is instructive. Cortland --- 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
Re: Use of PCB Traces as Fuse and Voltage suppressor
Jim, You touch on an important issue concerning a fuse - just how does it blow? Years ago I discovered by accident that fuses were designed with some remarkable properties, when we had to make our own transient generator to verify some telcom equipment's compliance to a BABT power supply transient spec. The BABT spec required that you simulate some very husky power transients. It was like a short occurs in adjacent electronics followed by the inductive kick. The -48 voltage would clamp to around 10 volts then pop up to over 300 volts capable of supplying 500A for something like more than 50mS. If you didn't design your protection properly you would have a lot of unintentional PCB trace fuses. [ Actually heard that the spec originated because a workman had dropped his wrench across the 1 inch diameter rods which supply the -48 to the telco building from the battery building. After the wrench evaporated, they found the whole room of equipment was blown, thus the spec. Somebody verify that? ] The simulator used 4 deep discharge current vehicle batteries supplying the telcom equipment through 50uH of inductance (that was cable on a spool). Parallel to that you used a starter solenoid to short out a fuse with a dead short. Amazingly the larger fuses never produced much kick back. They were designed to blow gently away. Tried all kinds. Most of the 8AG didn't do much, other types, nothing, even the 100 amp cartridge types, nothing, The absolute best was a 1A 8AG type. When that went, you'd get a flash of light, 300 volts trying to drive 500 amps into everything, and even the coil would jump up off the floor. Talk about PCB traces acting like fuses. Anyway, I learned a respect for people who design fuses to make them go away so gently when there is an incredible potential for some extremely high voltage transients. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: Jim Bacher jim.bac...@paxar.com To: 'Cortland Richmond' 72146@compuserve.com; Chris Maxwell chris.maxw...@nettest.com; ieee pstc list emc-p...@ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, February 25, 2002 3:04 PM Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor Long time ago we found that the traces worked well as fuses when the batteries were fully charged. However, when the batteries were mostly discharged, the PC Board traces did not work well as fuses. At lower battery charge levels, the traces became very hot and ignited the PC Board rather than opening the traces up. I therefore would recommend against using PC Board traces as fuses. Jim Jim Bacher, Senior Engineer Paxar Corp. e-mail: jim.bac...@paxar.com or j.bac...@ieee.org voice: 1-937-865-2020 fax: 1-937-865-2048 -Original Message- From: Cortland Richmond [mailto:72146@compuserve.com] Sent: Thursday, February 21, 2002 12:53 AM To: Chris Maxwell; ieee pstc list Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor When do you need a fuse? Level II is the only time you are allowed to lose functionality, and the requirement for THAT is, it can't catch fire or explode. I've seen trace fuses tried. The problem comes after the trace blows. You are at the mercy of your board shop, and if you use a number of them, results might not be all that repeatable. AS i said earlier, I've had a board catch fire in my hand (though not as a result of stress, but a solder splash). It is instructive. Cortland --- 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 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:
RE: Use of PCB Traces as Fuse and Voltage suppressor
Long time ago we found that the traces worked well as fuses when the batteries were fully charged. However, when the batteries were mostly discharged, the PC Board traces did not work well as fuses. At lower battery charge levels, the traces became very hot and ignited the PC Board rather than opening the traces up. I therefore would recommend against using PC Board traces as fuses. Jim Jim Bacher, Senior Engineer Paxar Corp. e-mail: jim.bac...@paxar.com or j.bac...@ieee.org voice: 1-937-865-2020 fax: 1-937-865-2048 -Original Message- From: Cortland Richmond [mailto:72146@compuserve.com] Sent: Thursday, February 21, 2002 12:53 AM To: Chris Maxwell; ieee pstc list Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor When do you need a fuse? Level II is the only time you are allowed to lose functionality, and the requirement for THAT is, it can't catch fire or explode. I've seen trace fuses tried. The problem comes after the trace blows. You are at the mercy of your board shop, and if you use a number of them, results might not be all that repeatable. AS i said earlier, I've had a board catch fire in my hand (though not as a result of stress, but a solder splash). It is instructive. Cortland --- 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: Use of PCB Traces as Fuse and Voltage suppressor
Gas discharge tubes can be very complex devices and have a number of specifications. Normally the voltage spec that you see is the DC specification, in other words, the firing voltage if the voltage is slowly ramped up (2kV/second is on rate used); however, the impulse voltage -- the voltage at which the tube fires with a fast pulse (anywhere from 100V/us to 10kV/us) is normally much higher. One of the objectives in gas tube design is to get the DC and impulse voltages to be as consistent as possible, and as close together as possible (actually very difficult). Gas mixtures, doping, electrode geometry, etc. are all critical to the design. Some gas is sensitive to light, some work better in the light and for a while, some were doped with radioactivity to help control the firing point under different voltage impulse conditions. Hope this helps Nothing's ever simple. Best Regards, Mike Hopkins Thermo KeyTek. -Original Message- From: Robert Macy [mailto:m...@california.com] Sent: Wednesday, February 20, 2002 7:18 PM To: Chris Maxwell; bogda...@pacbell.net Cc: EMC-PSTC Internet Forum Subject: Re: Use of PCB Traces as Fuse and Voltage suppressor Our experience with gas discharge tubes was that they worked according to spec in the lab. fired perfectly around 400V like they're supposed to, but down inside of the PVC oil tank holding the 150KV isolation transformer they liked to fire at 600V+ Guess they needed photon energy to make the gas trigger or something. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: Chris Maxwell chris.maxw...@nettest.com To: bogda...@pacbell.net bogda...@pacbell.net Cc: EMC-PSTC Internet Forum emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Wednesday, February 20, 2002 2:15 PM Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor Hi Bogdan, I'm sorry if you thought that my previous message was an endorsement for using necked down PCB traces as a fuse. I understand and share the sentiment that it is an unpredictable and probably not even cost effective solution. I was wondering why anyone would shape a PCB trace in such a way (two triangles pointing at each other with a thin trace between the points). A fuse is probably not the likely intention. A reasonable explanation may be a cut jumper. The triangles make the trace visible; while the thin trace provides an easy spot for the trace to be cut with an exacto knife which permanently removes the jumper.Another reason (suggested by a colleage) are alignment marks used by the PCB fab house to help align layers. Just to be sure... I'm not suggesting the above as design ideas. I'm just trying to figure out why anyone would do such a thing. One solution to the original problem that I haven't seen suggested is the good old air discharge tube, gas-discharge tube, gas tube ...whatever you want to call them. Of course, they aren't free (about $1 each). They are more predictable than open air terminals, they are UL/CSA recognized and they can handle some massive breakdown currents. They are available from Bourns and Sankosha USA... probably some other manufacturers as well. Chris -Original Message- From: bogdan matoga [SMTP:bogda...@pacbell.net] Sent: Wednesday, February 20, 2002 4:19 PM To: gab...@simex.ca; Chris Maxwell; emc-p...@mahordomo.ieee.org Subject: Use of PCB Traces as Fuse and Voltage suppressor Gabi: I believe that there is a basic rule which is not published anywhere: when you design something, then do it right. When transient suppressors are needed, then use the correct component, which will not depend on Paschen's Law and give predictable performance. Same for necked down fuses. When you want performance, then do it right. The above original suggestions are perfect for Mickey-Mouse-engineering. Bogdan. --- 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 message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit
RE: Use of PCB Traces as Fuse and Voltage suppressor
When do you need a fuse? Level II is the only time you are allowed to lose functionality, and the requirement for THAT is, it can't catch fire or explode. I've seen trace fuses tried. The problem comes after the trace blows. You are at the mercy of your board shop, and if you use a number of them, results might not be all that repeatable. AS i said earlier, I've had a board catch fire in my hand (though not as a result of stress, but a solder splash). It is instructive. Cortland --- 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: Use of PCB Traces as Fuse and Voltage suppressor
Our experience with gas discharge tubes was that they worked according to spec in the lab. fired perfectly around 400V like they're supposed to, but down inside of the PVC oil tank holding the 150KV isolation transformer they liked to fire at 600V+ Guess they needed photon energy to make the gas trigger or something. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: Chris Maxwell chris.maxw...@nettest.com To: bogda...@pacbell.net bogda...@pacbell.net Cc: EMC-PSTC Internet Forum emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Wednesday, February 20, 2002 2:15 PM Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor Hi Bogdan, I'm sorry if you thought that my previous message was an endorsement for using necked down PCB traces as a fuse. I understand and share the sentiment that it is an unpredictable and probably not even cost effective solution. I was wondering why anyone would shape a PCB trace in such a way (two triangles pointing at each other with a thin trace between the points). A fuse is probably not the likely intention. A reasonable explanation may be a cut jumper. The triangles make the trace visible; while the thin trace provides an easy spot for the trace to be cut with an exacto knife which permanently removes the jumper.Another reason (suggested by a colleage) are alignment marks used by the PCB fab house to help align layers. Just to be sure... I'm not suggesting the above as design ideas. I'm just trying to figure out why anyone would do such a thing. One solution to the original problem that I haven't seen suggested is the good old air discharge tube, gas-discharge tube, gas tube ...whatever you want to call them. Of course, they aren't free (about $1 each). They are more predictable than open air terminals, they are UL/CSA recognized and they can handle some massive breakdown currents. They are available from Bourns and Sankosha USA... probably some other manufacturers as well. Chris -Original Message- From: bogdan matoga [SMTP:bogda...@pacbell.net] Sent: Wednesday, February 20, 2002 4:19 PM To: gab...@simex.ca; Chris Maxwell; emc-p...@mahordomo.ieee.org Subject: Use of PCB Traces as Fuse and Voltage suppressor Gabi: I believe that there is a basic rule which is not published anywhere: when you design something, then do it right. When transient suppressors are needed, then use the correct component, which will not depend on Paschen's Law and give predictable performance. Same for necked down fuses. When you want performance, then do it right. The above original suggestions are perfect for Mickey-Mouse-engineering. Bogdan. --- 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: Use of PCB Traces as Fuse and Voltage suppressor
I read in !emc-pstc that Chris Maxwell chris.maxw...@nettest.com wrote (in 83d652574e7af740873674f9fc12dbaaf7d...@utexh1w2.gnnettest.com) about 'Use of PCB Traces as Fuse and Voltage suppressor', on Wed, 20 Feb 2002: I'm sorry if you thought that my previous message was an endorsement for using necked down PCB traces as a fuse. I understand and share the sentiment that it is an unpredictable and probably not even cost effective solution. It is an effective way of coping with the problem of protecting against a (highly improbable) almost direct short-circuit of a high-energy battery. -- 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
RE: Use of PCB Traces as Fuse and Voltage suppressor
Hi Bogdan, I'm sorry if you thought that my previous message was an endorsement for using necked down PCB traces as a fuse. I understand and share the sentiment that it is an unpredictable and probably not even cost effective solution. I was wondering why anyone would shape a PCB trace in such a way (two triangles pointing at each other with a thin trace between the points). A fuse is probably not the likely intention. A reasonable explanation may be a cut jumper. The triangles make the trace visible; while the thin trace provides an easy spot for the trace to be cut with an exacto knife which permanently removes the jumper.Another reason (suggested by a colleage) are alignment marks used by the PCB fab house to help align layers. Just to be sure... I'm not suggesting the above as design ideas. I'm just trying to figure out why anyone would do such a thing. One solution to the original problem that I haven't seen suggested is the good old air discharge tube, gas-discharge tube, gas tube ...whatever you want to call them. Of course, they aren't free (about $1 each). They are more predictable than open air terminals, they are UL/CSA recognized and they can handle some massive breakdown currents. They are available from Bourns and Sankosha USA... probably some other manufacturers as well. Chris -Original Message- From: bogdan matoga [SMTP:bogda...@pacbell.net] Sent: Wednesday, February 20, 2002 4:19 PM To: gab...@simex.ca; Chris Maxwell; emc-p...@mahordomo.ieee.org Subject: Use of PCB Traces as Fuse and Voltage suppressor Gabi: I believe that there is a basic rule which is not published anywhere: when you design something, then do it right. When transient suppressors are needed, then use the correct component, which will not depend on Paschen's Law and give predictable performance. Same for necked down fuses. When you want performance, then do it right. The above original suggestions are perfect for Mickey-Mouse-engineering. Bogdan. --- 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
