Big crowbar module for <4VDC?
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From: Phil Hobbs on 19 Dec 2008 17:12 Phil Hobbs wrote: > Joerg wrote: >> Phil Hobbs wrote: >>> Jim Thompson wrote: >>> >>>> [snip] >>>> >>>> Your numbers match up to mine, protecting a 5V/20A system. >>>> >>>> I saw about a 1000A pulse, only sound was like a faint "click". >>>> >>>> High speed video of the fuse showed the whole segment vaporizing in >>>> ~1usec ;-) >>> >>> Egg-nog overdose alert! What sort of video system was that, exactly? >>> 10^6 frames per second and what, 1000 frames or more? >>> >> >> Check out this series: >> http://www.dubtronic.de/galerie/1280/36/s_003.html >> >> He did that on his kitchen table, gun and all! >> >> http://www.dubtronic.de/galerie/1280/36/s_014.html >> >> [...] >> > > > Very Edgertonesque, except that that's a pellet gun--they don't let them > have real firearms over there anymore, I gather. > > Cheers, > > Phil Hobbs Also, his Leibniz cookies have no chocolate. What a wasted opportunity. (Choco-Leibniz is my son's favourite cookie in the world.) Cheers, Phil Hobbs
From: Jim Thompson on 19 Dec 2008 17:17 On Fri, 19 Dec 2008 17:01:43 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >Jim Thompson wrote: >> On Fri, 19 Dec 2008 16:41:32 -0500, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> Jim Thompson wrote: >>> >>>> [snip] >>>> >>>> Your numbers match up to mine, protecting a 5V/20A system. >>>> >>>> I saw about a 1000A pulse, only sound was like a faint "click". >>>> >>>> High speed video of the fuse showed the whole segment vaporizing in >>>> ~1usec ;-) >>> Egg-nog overdose alert! What sort of video system was that, exactly? >>> 10^6 frames per second and what, 1000 frames or more? >>> >>>> Slow-blow fuses are for fairies and leftist weenies ;-) >>>> >>>> ...Jim >>> Cheers, >>> >>> Phil Hobbs >> >> Smear camera. Actual break time was measured electrically. Video >> showed... now you see it... now you see it glow... now you see Rudolph >> gone ;-) >> >> ...Jim Thompson > >Okay, understood. Optics people don't call streak cameras 'video'. ;) > >You have my official permission to have another eggnog. > >Cheers, > >Phil Hobbs No nog yet. Though I did have a nice, until today unknown to me, "Tunnel of Elms" Cabernet with lunch... quite nice and inexpensive. Found a nice new place for lunch, near Chandler Mall, in spite of its quite paisano name, "Nouveau Bistro" ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
From: Jim Thompson on 19 Dec 2008 17:45 On Fri, 19 Dec 2008 14:09:44 -0800, Joerg <notthisjoergsch(a)removethispacbell.net> wrote: >Jim Thompson wrote: >> On Fri, 19 Dec 2008 13:49:28 -0800, Joerg >> <notthisjoergsch(a)removethispacbell.net> wrote: >> >>> Phil Hobbs wrote: >>>> Jim Thompson wrote: >>>> >>>>> [snip] >>>>> >>>>> Your numbers match up to mine, protecting a 5V/20A system. >>>>> >>>>> I saw about a 1000A pulse, only sound was like a faint "click". >>>>> >>>>> High speed video of the fuse showed the whole segment vaporizing in >>>>> ~1usec ;-) >>>> Egg-nog overdose alert! What sort of video system was that, exactly? >>>> 10^6 frames per second and what, 1000 frames or more? >>>> >>> Check out this series: >>> http://www.dubtronic.de/galerie/1280/36/s_003.html >>> >>> He did that on his kitchen table, gun and all! >>> >>> http://www.dubtronic.de/galerie/1280/36/s_014.html >>> >>> [...] >> >> My wife worked for Doc Edgerton while I was a student at MIT. >> > >Doc must have been one of the greatest professors ever. Played a mean guitar and had steak cook-outs right there in his lab... a wonder we all didn't die of carbon monoxide ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
From: Chris Jones on 19 Dec 2008 19:03 Jim Thompson wrote: > On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams > <tmoranwms(a)gmail.com> wrote: > >>On Dec 17, 7:12 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >>Web-Site.com> wrote: >>> Second question. You _are_ aware that the crowbar goes on the _input_ >>> side of the linear regulator, aren't you ?:-) >> >>Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >>also recommend putting the crowbar at the output? Which is, >>incidentially, the logical place to put it when you want to protect >>$10k equipment powered by said supply anyway. Equipment >> supply, >>protect equipment. QED. >> >>Tim > > Where did you hear that I respected AoE? > > It's nothing more than a compendium of circuits... somewhat on a par > with Ideas for Design, are they not? > > Crowbar on input side of a linear regulator is ideal for speed and > efficacy of fuse blowing. > > Crowbar on the output side is a prayer... hope it can sink more > current than the faulty regulator can deliver, and that the resultant > heating won't violate the various regulatory rules that Joerg worries > more about than good engineering practice... when that melts, then > there's the spike that takes out $BIG load anyway ;-) > > But I suppose there _are_ people who fret over spending $1 to protect > $BIG load <smirk> > > ...Jim Thompson A lot of people have learnt a lot of very useful things from AoE, and the world is significantly better off for its existence. I do agree that the fuse and crowbar SCR should preferably go before the regulator, especially if the transformer is not protected by a fuse in the secondary that will always blow before the transformer overheats (which is difficult unless the transformer is grossly oversized), and/or a thermal cutout in the windings. It can be even more difficult to choose the rating of the fuse in the primary of the transformer such that it will always blow when a steady overload appears at the regulator output, yet does not blow in normal circumstances due to inrush current. Unless there is a thermal cutout in the transformer itself, it may be possible in some cases to set fire to the transformer without first blowing the primary fuse. That could damage the expensive load by purely thermal means (flames, etc.), even if no electrical damage is caused. It is probably worthwhile working out exactly how the current is going to be cut off after the crowbar fires. Putting the fuse and crowbar switching device before the regulator (obviously with the voltage sensing connection after the regulator) sounds like one good way whereby the likelihood of blowing the fuse cleanly could be predicted, with a suitably large capacitor and SCR. Other arrangements might require more analysis and/or testing. Chris
From: Phil Hobbs on 19 Dec 2008 18:07
Chris Jones wrote: > Jim Thompson wrote: > >> On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams >> <tmoranwms(a)gmail.com> wrote: >> >>> On Dec 17, 7:12 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >>> Web-Site.com> wrote: >>>> Second question. You _are_ aware that the crowbar goes on the _input_ >>>> side of the linear regulator, aren't you ?:-) >>> Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >>> also recommend putting the crowbar at the output? Which is, >>> incidentially, the logical place to put it when you want to protect >>> $10k equipment powered by said supply anyway. Equipment >> supply, >>> protect equipment. QED. >>> >>> Tim >> Where did you hear that I respected AoE? >> >> It's nothing more than a compendium of circuits... somewhat on a par >> with Ideas for Design, are they not? >> >> Crowbar on input side of a linear regulator is ideal for speed and >> efficacy of fuse blowing. >> >> Crowbar on the output side is a prayer... hope it can sink more >> current than the faulty regulator can deliver, and that the resultant >> heating won't violate the various regulatory rules that Joerg worries >> more about than good engineering practice... when that melts, then >> there's the spike that takes out $BIG load anyway ;-) >> >> But I suppose there _are_ people who fret over spending $1 to protect >> $BIG load <smirk> >> >> ...Jim Thompson > > A lot of people have learnt a lot of very useful things from AoE, and the > world is significantly better off for its existence. > > I do agree that the fuse and crowbar SCR should preferably go before the > regulator, especially if the transformer is not protected by a fuse in the > secondary that will always blow before the transformer overheats (which is > difficult unless the transformer is grossly oversized), and/or a thermal > cutout in the windings. > > It can be even more difficult to choose the rating of the fuse in the > primary of the transformer such that it will always blow when a steady > overload appears at the regulator output, yet does not blow in normal > circumstances due to inrush current. > > Unless there is a thermal cutout in the transformer itself, it may be > possible in some cases to set fire to the transformer without first blowing > the primary fuse. That could damage the expensive load by purely thermal > means (flames, etc.), even if no electrical damage is caused. > > It is probably worthwhile working out exactly how the current is going to be > cut off after the crowbar fires. Putting the fuse and crowbar switching > device before the regulator (obviously with the voltage sensing connection > after the regulator) sounds like one good way whereby the likelihood of > blowing the fuse cleanly could be predicted, with a suitably large > capacitor and SCR. Other arrangements might require more analysis and/or > testing. > > Chris > And the 'working out' has to include the well-known human tendency to cut corners and then lie to cover it up--I'd want to wear a belt and suspenders there. I've seen too many people use fuses wrapped in foil. Cheers, Phil Hobbs |