On Sunday 09 December 2012 07:50:34 dave did opine: > On Sat, 2012-12-08 at 23:56 -0500, Gene Heskett wrote: > > On Saturday 08 December 2012 23:49:28 Jon Elson did opine: > > > Gene, > > > > > > You can get aircraft breakers, designed for 32 V DC, and some are > > > quite small. They have push/pull kinds that pop out when tripped, > > > and bat handle types used as on/off switches, too. New can be > > > expensive, but they may be available on the surplus market. > > > I have a few. > > > > > > Jon > > > > That too might be a possibility, but not until I have explored the > > options for some sort of an excessive pid.error out shutdown that > > works fast enough to save the fuse 90% or more of the time. My > > previous lashup using comp worked well about 75% of the time. > > > > OTOH, tripping a breaker the first 100 times is generally free. Once > > the breaker has been paid for... And at this current level, it > > really should last a lot longer than that. > > > > Cheers, Gene > > Many years ago I was using a Heinemann magnetic breaker in series with > an I^2R fuse to protect a pair of SCR's. On a fault the breaker always > beat the fuse thereby saving rather expensive fuses. > > Dave
Heinamann's breakers do have a failure mode I don't care for. A 3 phase, 40 amp, running a 20 hp waterpump for cooling the klystrons at KXNE-TV failed in the middle of the morning of the broadcast day, about 10 minutes after I had walked into the building and had turned on all the monitors to check on its general health. I was standing in front of the control console when I heard a motor get single phased. My hand made it about half way of the 30" to the beam power off button before the lights went out because the buildings entrance breaker, a 1200 amp Westinghouse went down with a bang like a 10 ga shotgun. That of course started the 335 cummalong standby so I had lights in 5 or 6 seconds. The post mortem disclosed that the center phase contacts in that breaker were burned to a crisp, the pump itself was fine, and that the visual klystron was shorted, full of very highly deionized water where a very good vacuum was supposed to be. Apparently the beam had pierced the beam collector funnel at the bottom of the tube, fairly easy when there isn't 70 gallons a minute flowing around it to cool it. The beam currant is about 5.7 amps, with just short of 20 kilovolts pushing it, for a total heat input of about 120kw. They had to call in a quorum of the Nebraska Legislature (its a unicameral system and was not in session at the time) and pass a bill authorizing the purchase of a new klystron for me. They were, in '75, only $150,000 each. Had that $200 breaker not failed, that klystron would have functioned another 4 or 5 years. That little incident got a circuit made up that watched the 3 cables going to the pump, which is a phase sneezed for about a cycle, opened and latched open a 50kv, 50 amp rated vacuum relay in series with the wire to the tubes cathodes. The supply, a 3 phase bridge, choke input filter, had 20 kv rated capacitors in it. Suddenly disconnecting a 10 ampere load sent the supply to nearly 40 kv until it bled off, as that trip cascaded back an opened the GE AK-225 breaker that fed those 3 pole cans wired backwards to make that high voltage. Even if one of those caps would have failed, it was way cheaper than a new klystron. That failure would have been quite a show, 32 u-farads with 38kv in them would be about what the N.I.F. is using to fire one laser in that boondoggle we've put trillions into by now. Probably one hell of a mess to clean up too. Only so much you can expect a 14"x14"x7" tin can full of pcb's to contain. Broadcasting can be an expensive, interesting line of work. I am probably one of the last 20 people in the country that can lift one of those out of its shipping cradle, dress it up with all the cavities, set it down into its 2200 lb magnet/dolly, hook it up, tune and adjust it for use. One wrong magnet adjustment, for 20 milliseconds, and you have another $150,000 worth of junk. But now its a dead talent. That technology was replaced 30 years ago with a more efficient technology, and broadcasters, looking at their 4 and 5 digit monthly power bills didn't waste a lot of time switching. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! It usually takes more than three weeks to prepare a good impromptu speech. -- Mark Twain I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
