Big crowbar module for <4VDC?
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From: Joerg on 19 Dec 2008 18:38 Phil Hobbs wrote: > 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. > Archie Bunker put a penny underneath. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 19 Dec 2008 18:46 On Fri, 19 Dec 2008 15:38:41 -0800, Joerg <notthisjoergsch(a)removethispacbell.net> wrote: >Phil Hobbs wrote: >> 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. >> > >Archie Bunker put a penny underneath. I've been known to cure recalcitrant equipment by sawing off a piece of pot shaft as a replacement for a fuse ;-) ...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 18:50 On Sat, 20 Dec 2008 00:03:42 +0000, Chris Jones <lugnut808(a)yahoo.com> 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. Indeed. > >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. Thank you! Finally someone understands! > >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 My approach had the storage cap, the fuse, and the SCR in a _very_ tight loop, with wide traces. I have even been known to solder bus bar on top of this path to ensure that high currents are reached quickly ;-) ...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: Joerg on 19 Dec 2008 19:10 Jim Thompson wrote: > On Sat, 20 Dec 2008 00:03:42 +0000, Chris Jones <lugnut808(a)yahoo.com> > 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. > > Indeed. > >> 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. > > Thank you! Finally someone understands! > A transformer that overheats before the primary fuse goes is a serious design flaw. Either the thermoswitch must open or the fuse. What else would protect upon overload caused be a faulty electrolytic? Unless you pepper the whole unit with fuses. >> 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 > > My approach had the storage cap, the fuse, and the SCR in a _very_ > tight loop, with wide traces. I have even been known to solder bus > bar on top of this path to ensure that high currents are reached > quickly ;-) > Just received another schematic, for da big mother of all linear supplies. The one that needs modding. The SCR is, tada, you guessed it, on the output. Rock-solid American manufacturer, in business since 1973. Good products, top notch customer service (I had the schematic within the hour). The SCR is a serious edition, size of a silver Dollar. If you do the super high current spike thing (I wouldn't, but you know that by now) make sure they never put in a plain old glass fuse. Exploding glass is no fun. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Chris Jones on 19 Dec 2008 21:16
Joerg wrote: > Jim Thompson wrote: >> On Sat, 20 Dec 2008 00:03:42 +0000, Chris Jones <lugnut808(a)yahoo.com> >> 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. >> >> Indeed. >> >>> 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. >> >> Thank you! Finally someone understands! >> > > A transformer that overheats before the primary fuse goes is a serious > design flaw. Either the thermoswitch must open or the fuse. Yes, but it is not at all trivial to get it to work without the thermoswitch. If I were to hang my crowbar on someone else's PSU, then I guess I might feel duty bound to know the likely and less likely outcomes of the crowbar being activated, in the presence of whatever fault inside the PSU was the original cause of the overvoltage (so maybe the current limit doesn't work right anymore, etc.). Perhaps that is doing the PSU designer's job for them. > What else would protect upon overload caused be a faulty electrolytic? > Unless you pepper the whole unit with fuses. I agree that the transformer should ideally be protected from fire in the case of a long term short circuit appearing at its output, as well as any current between normal and the short circuit current. The worst case is probably not a short circuit (if this blows the fuse) but rather whatever current nearly but not quite blows the fuse (and there is some manufacturing variation in fuses too, even the non-user-replaceable ones). I am wary of the possibility that the original design did not necessarily achieve this degree of protection. I am not sure what is legally required but I have seen some commercial designs that worry me. Admittedly it is mostly smaller transformers than the one you are looking at, where I worry that the primary current with a nearly-shorted secondary is not quite enough to blow a primary fuse. In things like wall warts I am much more reassured when there is a thermal cutout embedded in the primary winding as well. Maybe I'm being paranoid and the flame retardants in the modern insulation are possibly better than I have assumed. I have had an old waxed-paper transformer catch fire in some audio equipment (without blowing the fuse), fortunately whilst I was there in the room to unplug it, but that experience did make me look at transformers with more suspicion. >>> 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 >> >> My approach had the storage cap, the fuse, and the SCR in a _very_ >> tight loop, with wide traces. I have even been known to solder bus >> bar on top of this path to ensure that high currents are reached >> quickly ;-) >> > > Just received another schematic, for da big mother of all linear > supplies. The one that needs modding. The SCR is, tada, you guessed it, > on the output. Rock-solid American manufacturer, in business since 1973. > Good products, top notch customer service (I had the schematic within > the hour). > > The SCR is a serious edition, size of a silver Dollar. How do they cut off the current after the SCR fires? Is it the primary fuse, or maybe the pass transistor emitter bondwire? I guess they tested it at some stage. > If you do the super high current spike thing (I wouldn't, but you know > that by now) make sure they never put in a plain old glass fuse. > Exploding glass is no fun. > The fuses that they use in mains plugs in the UK are surprisingly robust. I'm not sure what the official rating is but they are made of ceramic not glass and they are filled with sand. They are used in such large numbers that the price is very very low. Chris |