Big crowbar module for <4VDC?
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From: Jim Thompson on 19 Dec 2008 10:24 On Fri, 19 Dec 2008 15:06:56 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Fri, 19 Dec 2008 07:53:00 -0700) it happened Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in ><q9dnk45qjgfe4u4upnc3a7kvpivet4f0r1(a)4ax.com>: > >>On Fri, 19 Dec 2008 10:51:25 GMT, Jan Panteltje >><pNaonStpealmtje(a)yahoo.com> wrote: > >>>Crowbars are to protect the LOAD, not the supply, and should be at the OUTPUT. >>>In case of a 100K$ load and a 100$ supply, the choice is easy. >>>Shorting before the regulator does not guarantee energy in any caps and >>>or inductors in the circuit does not make it to the load. >>>Simple. >> >>Nope. Simple-minded analysis. > >Maybe you can address this issue: > > 'Shorting before the regulator does not guarantee energy in any caps and > or inductors in the circuit does not make it to the load.' > >versus insulting, you leftist commie ;-) > [snip] Naaah! YOU be the leftist commie jerk. ...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: Jan Panteltje on 19 Dec 2008 10:59 On a sunny day (Fri, 19 Dec 2008 08:24:29 -0700) it happened Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in <93fnk4tcqa4vd6lrtiuo6rrel6r33nrbl1(a)4ax.com>: >>Maybe you can address this issue: >> >> 'Shorting before the regulator does not guarantee energy in any caps and >> or inductors in the circuit does not make it to the load.' >> >>versus insulting, you leftist commie ;-) >> >[snip] > >Naaah! YOU be the leftist commie jerk. That begs the question not only about your knowledge of crowbars, but also if you know the difference between left and right. You can test it here: http://en.citizendium.org/wiki/Right-hand_screw_rule
From: Joerg on 19 Dec 2008 12:21 Jim Thompson wrote: > On Fri, 19 Dec 2008 10:51:25 GMT, Jan Panteltje > <pNaonStpealmtje(a)yahoo.com> wrote: > >> On a sunny day (Thu, 18 Dec 2008 18:32:11 -0800) it happened Joerg >> <notthisjoergsch(a)removethispacbell.net> wrote in >> <TID2l.10279$yr3.2278(a)nlpi068.nbdc.sbc.com>: >> >>>> http://www.hobbyprojects.com/thyristor_triac_and_diac/thyristor_as_a_crowbar.html >>>> >>> Has the author ever heard of a gate trigger voltage? Assume 1.5V for >>> now: Zener 5.1V plus Vgt = 6.6V. Phssst ... crackle ... pop ... *BANG* >>> ... there goes the majority of connected logic chips. Many of those >>> won't take anything above 6V. >>> >>> The proper way to do a crowbar is with a TL431. >> Crowbars are to protect the LOAD, not the supply, and should be at the OUTPUT. >> In case of a 100K$ load and a 100$ supply, the choice is easy. >> Shorting before the regulator does not guarantee energy in any caps and >> or inductors in the circuit does not make it to the load. >> Simple. > > But, according to Joerg, $1 for a fuse is too much ;-) > Not in this case. In this case there simply is no way to install one without major surgery. In other cases (med/aero etc.) a fuse is always considered a fire risk. Because it is one. So every fuse will greatly increase a cert effort. So you only place them where they make sense. Between caps and pass devices they often don't. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Yzordderrex on 19 Dec 2008 12:57 Please allow me to interject my 3rd person impartiality on the subject of crobars. I've only designed one but it might interest you. The application was for a braking unit for a 20HP 480V three phase induction motor drive. The brake is a transistor in series with a braking resistor which is placed across the DC bus. When the buss voltage goes up due to the motor regenerating, the transistor turns on and the bus voltage is clamped into the brake resistor. If for any reason the brake stays on for too long then there is a good chance of a fire developing. If the brake transistor shorts there must be an alternate means to remove the bus voltage. A latching contactor on the input side would work, but is expensive to implement. I used a 90amp SCR module in order to crowbar the bus. The bus was 1000uF at about 700VDC. So the little 90amp scr took the bus voltage down to zero, and also cleared a pair of JJS-60 fuses. And the little scr remained intact to crowbar again if needed. I don;t remember all of the details as it was over 20 years ago, but one factoid I remember is that the currents got up around 7000AMPS! And there was a fairly loud Ker-Chunk noise and the wiring did jump a little . So the point I want to make here is that you might be surprised what kind of punishment a little TO-220 scr might take. The only advice I can give you is when it's time to crowbar don't be shy with the gate drive current. Use a tight loop and hit it hard. regards, Yzordderrex On Dec 18, 9:51 pm, Joerg <notthisjoerg...(a)removethispacbell.net> wrote: > Jim Thompson wrote: > > On Thu, 18 Dec 2008 18:19:08 -0800, Joerg > > <notthisjoerg...(a)removethispacbell.net> wrote: > > > [snip] > >> Hey, maybe you should have done an apprenticeship under Earl William > >> Muntz before going to MIT ;-) > > > My father had a policy of refusing to service Muntz TV's ;-) > > I can understand why. I did the same in Germany, there was a brand named > "Kuba" where I told neighbors that I won't fix those anymore. > > Hey, did you post a few MP3 tunes from your father yet? > > -- > Regards, Joerg > > http://www.analogconsultants.com/ > > "gmail" domain blocked because of excessive spam. > Use another domain or send PM.
From: Joerg on 19 Dec 2008 13:14
Yzordderrex wrote: > Please allow me to interject my 3rd person impartiality on the subject > of crobars. I've only designed one but it might interest you. > > The application was for a braking unit for a 20HP 480V three phase > induction motor drive. The brake is a transistor in series with a > braking resistor which is placed across the DC bus. When the buss > voltage goes up due to the motor regenerating, the transistor turns on > and the bus voltage is clamped into the brake resistor. If for any > reason the brake stays on for too long then there is a good chance of > a fire developing. If the brake transistor shorts there must be an > alternate means to remove the bus voltage. A latching contactor on > the input side would work, but is expensive to implement. > > I used a 90amp SCR module in order to crowbar the bus. The bus was > 1000uF at about 700VDC. So the little 90amp scr took the bus voltage > down to zero, and also cleared a pair of JJS-60 fuses. And the little > scr remained intact to crowbar again if needed. I don;t remember all > of the details as it was over 20 years ago, but one factoid I remember > is that the currents got up around 7000AMPS! And there was a fairly > loud Ker-Chunk noise and the wiring did jump a little . > Ker-chunk plus wire jump with a TO220? Amazing! > So the point I want to make here is that you might be surprised what > kind of punishment a little TO-220 scr might take. The only advice I > can give you is when it's time to crowbar don't be shy with the gate > drive current. Use a tight loop and hit it hard. > Maybe we place several regular OVP-type crowbars in there in parallel, hoping that if one of the TO220's go kablouie the next one will hang on. After all, this thing has to only act once. If it ever does they'll call me in anyhow so see what happened and why. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |