Fw: Inductive relay "kick"
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----- Original Message ----- From: "Carl, WCØV" <[hidden email]> To: <[hidden email]> Sent: Saturday, April 04, 2009 8:50 PM Subject: Re: [Elecraft] Inductive relay "kick" > Good point. The diode will conduct the back EMF minus internal voltage > when the supply voltage to the coil is removed. You do need a diode with a > high enough PIV rating. But even Radio Shack has silicon diodes with 1000 > PIV rating, 2 amps forward current rating at five for a dollar. > > We make electric actuators where I work, motors with internal rollerscrews > and often they get equipped with electric safety brakes (apply when power > is removed, release when power is applied). We normally supply 1N4007 > (1000 PIV rated forward bias) diodes with brake equipped motors. > > 50% of those you ask would do that. The other 50% would use a very fast > switching diode as you suggest. Both work just fine since the only job is > to conduct the EMF coming out of the coil when the actuating voltage is > removed. BUT you do need a diode with a high enough PIV rating. Some of > our bigger unsuppressed motor brake coils can spit out over 600 vdc when > the supply is removed. > > And yes some of our customers hook up the diode or the brake supply > backwards and blow the diode (if they don't blow the supply first). > Protection is gone, and the back EMF from the relay coil is free to blast > wherever it wants to go. > > I am sure the Elecraft relays are way below that. My point to Don was that > simply doubling the voltage rating of the coil to get the back EMF is way > off. A scope will tell the real tale. > > BTW I got yelled at by a medical tech who pointed out that the pain > (real - I tried the relay wire experiment myself) is the voltage going > right across your heart. To some, 450 vdc may be a very bad day. > > 73, Carl WC0V > > ----- Original Message ----- > From: "Bob" <[hidden email]> > To: "WCØV" <[hidden email]> > Sent: Saturday, April 04, 2009 2:07 PM > Subject: Re: [Elecraft] Inductive relay "kick" > > >> Hi Carl, >> >> What am I missing here? Using a regular silicon diode that >> has a fast switching time, or even better a Schottky diode wouldn't they >> clamp at the forward bias of the junction .7 volts of less. If not how >> long could you expect the diode to survive that abuse of 75v across the >> forward biased junction. If the diode then failed open you would never >> know your protection was gone. >> 73, >> Bob >> K2TK >> >> Carl wrote: >> >>>Don, seriously disagree about the magnitude of the "kick". For years I >>>taught a course on industrial installations and demo'ed the "kick" issue >>>by soldering two bare wire to the coil of a small Potter and Brumfield >>>"ice cube" 12 vdc relay. I would pick the biggest guy in the class to >>>hold the wires while I touched them to a nine-volt transistor radio >>>battery. And then watch as he would throw the relay across the room. A >>>reverse diode would vastly reduce the effect. >>> >>>Well, I got yelled at and was told "Hey, Stupid (and stupid wasn't the >>>word they used)! Put that on a storage scope to see what you're messing >>>with." The scope showed a spike of 450 vdc! The diode reduced it to less >>>than 75 vdc. >>>The magnitude is due mainly to the large inductance of the coil, but >>>until some measurements are taken, some caution is advised. The >>>inductance of any coil inside a K2 or K3 is bound to be much smaller. But >>>the phenomenon is the same. >>> >>>73, Carl WC0V >>>______________________________________________________________ >>>Elecraft mailing list >>>Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>Help: http://mailman.qth.net/mmfaq.htm >>>Post: mailto:[hidden email] >>> >>>This list hosted by: http://www.qsl.net >>>Please help support this email list: http://www.qsl.net/donate.html >>> >>> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Carl,
If you look at the datasheet for the relay driver used in the KPA100, you will find that it does indeed have integral clamping diodes. Based on that fact, the inductive kick in the KPA100 should be almost zero, but in reality, there will still be a residual hit. I believe that saying it should never be greater than twice the relay coil voltage is quite a conservative one - we were discussing the KPA100 application in particular, not back EMF in the general.sense. You are quite correct - without clamping, and relay coils with relatively low resistance, the back EMF can grow very large. The energy in an inductor (the relay coil is an inductor) is proportional to the inductance times the square of the current, and if the relay coil resistance is low, the square of the ON current through it can be very large. 73, Don W3FPR Carl wrote: >>>> Don, seriously disagree about the magnitude of the "kick". For years I >>>> taught a course on industrial installations and demo'ed the "kick" issue >>>> by soldering two bare wire to the coil of a small Potter and Brumfield >>>> "ice cube" 12 vdc relay. I would pick the biggest guy in the class to >>>> hold the wires while I touched them to a nine-volt transistor radio >>>> battery. And then watch as he would throw the relay across the room. A >>>> reverse diode would vastly reduce the effect. >>>> >>>> Well, I got yelled at and was told "Hey, Stupid (and stupid wasn't the >>>> word they used)! Put that on a storage scope to see what you're messing >>>> with." The scope showed a spike of 450 vdc! The diode reduced it to less >>>> than 75 vdc. >>>> The magnitude is due mainly to the large inductance of the coil, but >>>> until some measurements are taken, some caution is advised. The >>>> inductance of any coil inside a K2 or K3 is bound to be much smaller. But >>>> the phenomenon is the same. >>>> >>>> 73, Carl WC0V >>>> > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Fw: Inductive relay "kick"
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In reply to this post by Carl, WCØV
1N4007 diodes have a notoriously long switchover time. That's what makes them useful as a poor-man's PIN diode. They aren't quite so useful in back EMF suppression, though. If you use a fast diode, you should be able to keep the back EMF voltage down to the forward-bias voltage of the diode. On Apr 4, 2009, at 9:52 PM, Carl, WCØV wrote: > > ----- Original Message ----- > From: "Carl, WCØV" <[hidden email]> > To: <[hidden email]> > Sent: Saturday, April 04, 2009 8:50 PM > Subject: Re: [Elecraft] Inductive relay "kick" > > >> Good point. The diode will conduct the back EMF minus internal >> voltage >> when the supply voltage to the coil is removed. You do need a diode >> with a >> high enough PIV rating. But even Radio Shack has silicon diodes >> with 1000 >> PIV rating, 2 amps forward current rating at five for a dollar. >> >> We make electric actuators where I work, motors with internal >> rollerscrews >> and often they get equipped with electric safety brakes (apply when >> power >> is removed, release when power is applied). We normally supply 1N4007 >> (1000 PIV rated forward bias) diodes with brake equipped motors. >> >> 50% of those you ask would do that. The other 50% would use a very >> fast >> switching diode as you suggest. Both work just fine since the only >> job is >> to conduct the EMF coming out of the coil when the actuating >> voltage is >> removed. BUT you do need a diode with a high enough PIV rating. >> Some of >> our bigger unsuppressed motor brake coils can spit out over 600 vdc >> when >> the supply is removed. >> >> And yes some of our customers hook up the diode or the brake supply >> backwards and blow the diode (if they don't blow the supply first). >> Protection is gone, and the back EMF from the relay coil is free to >> blast >> wherever it wants to go. >> >> I am sure the Elecraft relays are way below that. My point to Don >> was that >> simply doubling the voltage rating of the coil to get the back EMF >> is way >> off. A scope will tell the real tale. >> >> BTW I got yelled at by a medical tech who pointed out that the pain >> (real - I tried the relay wire experiment myself) is the voltage >> going >> right across your heart. To some, 450 vdc may be a very bad day. >> >> 73, Carl WC0V >> >> ----- Original Message ----- >> From: "Bob" <[hidden email]> >> To: "WCØV" <[hidden email]> >> Sent: Saturday, April 04, 2009 2:07 PM >> Subject: Re: [Elecraft] Inductive relay "kick" >> >> >>> Hi Carl, >>> >>> What am I missing here? Using a regular silicon diode that >>> has a fast switching time, or even better a Schottky diode >>> wouldn't they >>> clamp at the forward bias of the junction .7 volts of less. If >>> not how >>> long could you expect the diode to survive that abuse of 75v >>> across the >>> forward biased junction. If the diode then failed open you would >>> never >>> know your protection was gone. >>> 73, >>> Bob >>> K2TK >>> >>> Carl wrote: >>> >>>> Don, seriously disagree about the magnitude of the "kick". For >>>> years I >>>> taught a course on industrial installations and demo'ed the >>>> "kick" issue >>>> by soldering two bare wire to the coil of a small Potter and >>>> Brumfield >>>> "ice cube" 12 vdc relay. I would pick the biggest guy in the >>>> class to >>>> hold the wires while I touched them to a nine-volt transistor radio >>>> battery. And then watch as he would throw the relay across the >>>> room. A >>>> reverse diode would vastly reduce the effect. >>>> >>>> Well, I got yelled at and was told "Hey, Stupid (and stupid >>>> wasn't the >>>> word they used)! Put that on a storage scope to see what you're >>>> messing >>>> with." The scope showed a spike of 450 vdc! The diode reduced it >>>> to less >>>> than 75 vdc. >>>> The magnitude is due mainly to the large inductance of the coil, >>>> but >>>> until some measurements are taken, some caution is advised. The >>>> inductance of any coil inside a K2 or K3 is bound to be much >>>> smaller. But >>>> the phenomenon is the same. >>>> >>>> 73, Carl WC0V >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[hidden email] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>>> >>>> >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html George William Coleman mail: [hidden email] Senior Software Developer phone: 770 978-0196 Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Web: http://boringhamradiopart.blogspot.com Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Bill:
Are you sure about this? A snubbing diode has to have fast turn on, but slower turn off is not as much of a concern. A while ago I looked at the turn on and turn off times for several diodes including the standard 1N4007 and found all sufficiently fast to work well as a relay snubbing device. Details are at http://www.cliftonlaboratories.com/diode_turn-on_time.htm Jack K8ZOA www.cliftonlaboratories.com Bill Coleman wrote: > 1N4007 diodes have a notoriously long switchover time. That's what > makes them useful as a poor-man's PIN diode. They aren't quite so > useful in back EMF suppression, though. > > If you use a fast diode, you should be able to keep the back EMF > voltage down to the forward-bias voltage of the diode. > > On Apr 4, 2009, at 9:52 PM, Carl, WCØV wrote: > > >> ----- Original Message ----- >> From: "Carl, WCØV" <[hidden email]> >> To: <[hidden email]> >> Sent: Saturday, April 04, 2009 8:50 PM >> Subject: Re: [Elecraft] Inductive relay "kick" >> >> >> >>> Good point. The diode will conduct the back EMF minus internal >>> voltage >>> when the supply voltage to the coil is removed. You do need a diode >>> with a >>> high enough PIV rating. But even Radio Shack has silicon diodes >>> with 1000 >>> PIV rating, 2 amps forward current rating at five for a dollar. >>> >>> We make electric actuators where I work, motors with internal >>> rollerscrews >>> and often they get equipped with electric safety brakes (apply when >>> power >>> is removed, release when power is applied). We normally supply 1N4007 >>> (1000 PIV rated forward bias) diodes with brake equipped motors. >>> >>> 50% of those you ask would do that. The other 50% would use a very >>> fast >>> switching diode as you suggest. Both work just fine since the only >>> job is >>> to conduct the EMF coming out of the coil when the actuating >>> voltage is >>> removed. BUT you do need a diode with a high enough PIV rating. >>> Some of >>> our bigger unsuppressed motor brake coils can spit out over 600 vdc >>> when >>> the supply is removed. >>> >>> And yes some of our customers hook up the diode or the brake supply >>> backwards and blow the diode (if they don't blow the supply first). >>> Protection is gone, and the back EMF from the relay coil is free to >>> blast >>> wherever it wants to go. >>> >>> I am sure the Elecraft relays are way below that. My point to Don >>> was that >>> simply doubling the voltage rating of the coil to get the back EMF >>> is way >>> off. A scope will tell the real tale. >>> >>> BTW I got yelled at by a medical tech who pointed out that the pain >>> (real - I tried the relay wire experiment myself) is the voltage >>> going >>> right across your heart. To some, 450 vdc may be a very bad day. >>> >>> 73, Carl WC0V >>> >>> ----- Original Message ----- >>> From: "Bob" <[hidden email]> >>> To: "WCØV" <[hidden email]> >>> Sent: Saturday, April 04, 2009 2:07 PM >>> Subject: Re: [Elecraft] Inductive relay "kick" >>> >>> >>> >>>> Hi Carl, >>>> >>>> What am I missing here? Using a regular silicon diode that >>>> has a fast switching time, or even better a Schottky diode >>>> wouldn't they >>>> clamp at the forward bias of the junction .7 volts of less. If >>>> not how >>>> long could you expect the diode to survive that abuse of 75v >>>> across the >>>> forward biased junction. If the diode then failed open you would >>>> never >>>> know your protection was gone. >>>> 73, >>>> Bob >>>> K2TK >>>> >>>> Carl wrote: >>>> >>>> >>>>> Don, seriously disagree about the magnitude of the "kick". For >>>>> years I >>>>> taught a course on industrial installations and demo'ed the >>>>> "kick" issue >>>>> by soldering two bare wire to the coil of a small Potter and >>>>> Brumfield >>>>> "ice cube" 12 vdc relay. I would pick the biggest guy in the >>>>> class to >>>>> hold the wires while I touched them to a nine-volt transistor radio >>>>> battery. And then watch as he would throw the relay across the >>>>> room. A >>>>> reverse diode would vastly reduce the effect. >>>>> >>>>> Well, I got yelled at and was told "Hey, Stupid (and stupid >>>>> wasn't the >>>>> word they used)! Put that on a storage scope to see what you're >>>>> messing >>>>> with." The scope showed a spike of 450 vdc! The diode reduced it >>>>> to less >>>>> than 75 vdc. >>>>> The magnitude is due mainly to the large inductance of the coil, >>>>> but >>>>> until some measurements are taken, some caution is advised. The >>>>> inductance of any coil inside a K2 or K3 is bound to be much >>>>> smaller. But >>>>> the phenomenon is the same. >>>>> >>>>> 73, Carl WC0V >>>>> ______________________________________________________________ >>>>> Elecraft mailing list >>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>> Post: mailto:[hidden email] >>>>> >>>>> This list hosted by: http://www.qsl.net >>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>> >>>>> >>>>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > > George William Coleman mail: [hidden email] > Senior Software Developer phone: 770 978-0196 > > Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] > Web: http://boringhamradiopart.blogspot.com > Quote: "Not within a thousand years will man ever fly!" > -- Wilbur Wright, 1901 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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There is a lesson here: before making any pronouncements, check Jack's website for the test results first. --- On Tue, 4/7/09, Jack Smith <[hidden email]> wrote: > From: Jack Smith <[hidden email]> > Subject: Re: [Elecraft] Fw: Inductive relay "kick" > To: "Bill Coleman" <[hidden email]> > Cc: [hidden email], "WCØV" <[hidden email]> > Date: Tuesday, April 7, 2009, 7:43 PM > Bill: > > Are you sure about this? A snubbing diode has to have fast > turn on, but > slower turn off is not as much of a concern. A while ago I > looked at the > turn on and turn off times for several diodes including > the standard > 1N4007 and found all sufficiently fast to work well as a > relay snubbing > device. Details are at > http://www.cliftonlaboratories.com/diode_turn-on_time.htm > > Jack K8ZOA > www.cliftonlaboratories.com > > > > Bill Coleman wrote: > > 1N4007 diodes have a notoriously long switchover time. > That's what > > makes them useful as a poor-man's PIN diode. They > aren't quite so > > useful in back EMF suppression, though. > > > > If you use a fast diode, you should be able to keep > the back EMF > > voltage down to the forward-bias voltage of the diode. > > > > On Apr 4, 2009, at 9:52 PM, Carl, WCØV wrote: > > > > > >> ----- Original Message ----- > >> From: "Carl, WCØV" > <[hidden email]> > >> To: <[hidden email]> > >> Sent: Saturday, April 04, 2009 8:50 PM > >> Subject: Re: [Elecraft] Inductive relay > "kick" > >> > >> > >> > >>> Good point. The diode will conduct the back > EMF minus internal > >>> voltage > >>> when the supply voltage to the coil is > removed. You do need a diode > >>> with a > >>> high enough PIV rating. But even Radio Shack > has silicon diodes > >>> with 1000 > >>> PIV rating, 2 amps forward current rating at > five for a dollar. > >>> > >>> We make electric actuators where I work, > motors with internal > >>> rollerscrews > >>> and often they get equipped with electric > safety brakes (apply when > >>> power > >>> is removed, release when power is applied). We > normally supply 1N4007 > >>> (1000 PIV rated forward bias) diodes with > brake equipped motors. > >>> > >>> 50% of those you ask would do that. The other > 50% would use a very > >>> fast > >>> switching diode as you suggest. Both work just > fine since the only > >>> job is > >>> to conduct the EMF coming out of the coil when > the actuating > >>> voltage is > >>> removed. BUT you do need a diode with a high > enough PIV rating. > >>> Some of > >>> our bigger unsuppressed motor brake coils can > spit out over 600 vdc > >>> when > >>> the supply is removed. > >>> > >>> And yes some of our customers hook up the > diode or the brake supply > >>> backwards and blow the diode (if they > don't blow the supply first). > >>> Protection is gone, and the back EMF from the > relay coil is free to > >>> blast > >>> wherever it wants to go. > >>> > >>> I am sure the Elecraft relays are way below > that. My point to Don > >>> was that > >>> simply doubling the voltage rating of the coil > to get the back EMF > >>> is way > >>> off. A scope will tell the real tale. > >>> > >>> BTW I got yelled at by a medical tech who > pointed out that the pain > >>> (real - I tried the relay wire experiment > myself) is the voltage > >>> going > >>> right across your heart. To some, 450 vdc may > be a very bad day. > >>> > >>> 73, Carl WC0V > >>> > >>> ----- Original Message ----- > >>> From: "Bob" <[hidden email]> > >>> To: "WCØV" > <[hidden email]> > >>> Sent: Saturday, April 04, 2009 2:07 PM > >>> Subject: Re: [Elecraft] Inductive relay > "kick" > >>> > >>> > >>> > >>>> Hi Carl, > >>>> > >>>> What am I missing here? Using a > regular silicon diode that > >>>> has a fast switching time, or even better > a Schottky diode > >>>> wouldn't they > >>>> clamp at the forward bias of the junction > .7 volts of less. If > >>>> not how > >>>> long could you expect the diode to survive > that abuse of 75v > >>>> across the > >>>> forward biased junction. If the diode > then failed open you would > >>>> never > >>>> know your protection was gone. > >>>> 73, > >>>> Bob > >>>> K2TK > >>>> > >>>> Carl wrote: > >>>> > >>>> > >>>>> Don, seriously disagree about the > magnitude of the "kick". For > >>>>> years I > >>>>> taught a course on industrial > installations and demo'ed the > >>>>> "kick" issue > >>>>> by soldering two bare wire to the coil > of a small Potter and > >>>>> Brumfield > >>>>> "ice cube" 12 vdc relay. I > would pick the biggest guy in the > >>>>> class to > >>>>> hold the wires while I touched them to > a nine-volt transistor radio > >>>>> battery. And then watch as he would > throw the relay across the > >>>>> room. A > >>>>> reverse diode would vastly reduce the > effect. > >>>>> > >>>>> Well, I got yelled at and was told > "Hey, Stupid (and stupid > >>>>> wasn't the > >>>>> word they used)! Put that on a storage > scope to see what you're > >>>>> messing > >>>>> with." The scope showed a spike > of 450 vdc! The diode reduced it > >>>>> to less > >>>>> than 75 vdc. > >>>>> The magnitude is due mainly to the > large inductance of the coil, > >>>>> but > >>>>> until some measurements are taken, > some caution is advised. The > >>>>> inductance of any coil inside a K2 or > K3 is bound to be much > >>>>> smaller. But > >>>>> the phenomenon is the same. > >>>>> > >>>>> 73, Carl WC0V > >>>>> > ______________________________________________________________ > >>>>> Elecraft mailing list > >>>>> Home: > http://mailman.qth.net/mailman/listinfo/elecraft > >>>>> Help: http://mailman.qth.net/mmfaq.htm > >>>>> Post: mailto:[hidden email] > >>>>> > >>>>> This list hosted by: > http://www.qsl.net > >>>>> Please help support this email list: > http://www.qsl.net/donate.html > >>>>> > >>>>> > >>>>> > >> > ______________________________________________________________ > >> Elecraft mailing list > >> Home: > http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:[hidden email] > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: > http://www.qsl.net/donate.html > >> > > > > George William Coleman mail: > [hidden email] > > Senior Software Developer phone: 770 > 978-0196 > > > > Bill Coleman, AA4LR, PP-ASEL Mail: > [hidden email] > > Web: http://boringhamradiopart.blogspot.com > > Quote: "Not within a thousand years will man ever > fly!" > > -- Wilbur Wright, 1901 > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[hidden email] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: > http://www.qsl.net/donate.html > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: > http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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