Big crowbar module for <4VDC?
in [Design]
|
Prev: Ultra-simple discrete 10W audio power stage for guitar use - would this work?
Next: Mitashi 4 GB Mp4 Player - MW156
From: Jim Thompson on 19 Dec 2008 16:33 On Fri, 19 Dec 2008 09:57:13 -0800 (PST), Yzordderrex <powersupplyguy(a)netzero.net> 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 . > >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 > > [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 ;-) Slow-blow fuses are for fairies and leftist weenies ;-) ...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: Phil Hobbs on 19 Dec 2008 16:41 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
From: Joerg on 19 Dec 2008 16:45 Jim Thompson wrote: > On Fri, 19 Dec 2008 09:57:13 -0800 (PST), Yzordderrex > <powersupplyguy(a)netzero.net> 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 . >> >> 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 >> >> > [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 ;-) > > Slow-blow fuses are for fairies and leftist weenies ;-) > You must have never used a serious electric welder. Fast-act breakers and fuses are a weight-loss program: Bphzt, bzzzzzzzzzzzzzzzzt, bzzzzzzt, bzzzzzzzzzzzzzzzzzt, clunk ... "S..t!". Up the stairs, toggle breaker, downs the stairs, back to the welder. It once took two dozen such trips until I had new hinges on a gate. -- 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 16:49 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 [...] -- 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 16:56
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 -- | 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 |