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 <[email protected]> wrote: > From: Jack Smith <[email protected]> > Subject: Re: [Elecraft] Fw: Inductive relay "kick" > To: "Bill Coleman" <[email protected]> > Cc: [email protected], "WCØV" <[email protected]> > 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" > <[email protected]> > >> To: <[email protected]> > >> 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" <[email protected]> > >>> To: "WCØV" > <[email protected]> > >>> 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:[email protected] > >>>>> > >>>>> 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:[email protected] > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: > http://www.qsl.net/donate.html > >> > > > > George William Coleman mail: > [email protected] > > Senior Software Developer phone: 770 > 978-0196 > > > > Bill Coleman, AA4LR, PP-ASEL Mail: > [email protected] > > 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:[email protected] > > > > 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:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
