I Don't Know Where The Big "BOOM" Came From!!! - Page 1
Forum section: electronics / testgear

author: Chris56000
author_rank: Frequent Contributor
timestamp: April 13, 2018, 12:03:57 am
content: Hi!I did an 18 month spell at a T & M Calibration/Repair house a few years ago, it wasn't a gratifying experience for me because of a personal dislike of me on the part of my immediate supervisor there, and also got a totally unjust accusation of deliberately damaging equipment!(Surely I can't be as bad at that former employer made out? I've had almost a lifetime doing everything from Radio & TV, to pc gear, T & M and industrials! If I do have a fault, it's getting engrossed in something far too deeply out of a desire to complete a repair and spending far more time than is cost–effective!)On a more light–hearted related note, I'd like to start this topic with all what my Brother–In–Law calls "Piff–Paff–Puff!!!" – tell us all about the worst accidental T & M equipment howlers that produced the most smoke, the biggest heartaches to repair, the most expensive "fuses" (things that blow to protect the actual glass fuse!) and disaster–tales that happen just when you think you've got it all working!Chris Williams

author: mzzj
author_rank: Super Contributor
timestamp: April 13, 2018, 08:05:47 am
content: 230 VAC to 0-1v input on some industrial measurement card. Both had same connectors so they got swapped at some point.Pretty much every IC on the card blew up, 5 meters of circuit traces vaporized and dozen of tantalum caps explode in fires and throw burning pieces of tantalum around.Multiple secondary fires around workbench from burning tantalum chipsTantalum cap pieces burn real hot!

author: CJay
author_rank: Super Contributor
timestamp: April 13, 2018, 11:44:03 am
content: Dunno, it breaks my heart every time I blow one of the 11A or 440mA fuses in my meters because it's such a dumb thing to do..The OhNoSecond, the period of time taken to realise you forgot to move the meter leads from the amps socket to the volts socket on a multimeter when trying to measure the voltage across a source capable of sourcing enough current to blast the arse out of the fuse in the meter and is always longer than the rupture time of the fuse.

author: Berni
author_rank: Super Contributor
timestamp: April 13, 2018, 12:27:58 pm
content: I haven't had any major catastrophic smoke generators so far.One i remember was when i was fixing a 4 channel HP rack mount PSU. One of its channels was dead so troubleshooted it for a while, found a useful test mode, poked my scope around and found a faulty quad opamp chip. I get the thing sucked out and replaced with a DIP socket, but after going trough my boxes of parts i couldn't find a opamp that had the right combination of specs to replace it. I really wanted to know of this is the only thing that was wrong so i looked for some more and found that i have some SOIC dual opamps that have the specs i need so i dead bug soldered a adapter that turns two of those into one DIP quad opamp. So i plug it into the socket and turn on the power supply, reaching for the buttons to go trough the menus and suddenly there was a pop and smoke coming out of it. I quickly turn it off and check where the smoke came out. It turned out it came from those dead bug wired opamps... upon closer inspection i plugged it into the socket the wrong way around.At that point i had enough and just went to order the correct replacement opamp from LT. Once it got here i stuck it into the socket (Paying a lot more attention to where pin 1 is this time around), i power up the PSU...no smoke this time, but the channel was still dead. More troubleshooting later i had no idea what was going wrong, it was having a different kind of fault, for a moment i thought i also blew up the DAC. Eventually i traced it down to a via being open circuit next to that opamp. Looks like the fault current from my backwards connected opamp blew it up. Fixed the via and suddenly the PSU works again.

author: GreyWoolfe
author_rank: Unknown
timestamp: April 13, 2018, 02:49:27 pm
content: Some years ago, someone gave me 2 tube scopes that someone gave him. Mind you, I didn't have a variac or dim bulb tester, now I have both. I just plugged the first one in and there was a trace. I plugged the second scope in and nothing. Noting that the plug in modules were the same model numbers in both scopes, I decided to swap them in one at a time into the working scope. The first scope was a rack mounted model, can't remember any details, without the covers on it. The first module went in and the scope came to a trace. When I plugged in the second module, there was a couple of loud pops and a 3 inch flame rose up out of the scope. I quickly unplugged the scope, however, the smell of what ever blew up lingered, actually for quite a few hours. Unfortunately, the smell was still strong when SWMBO came home from work. She was madder than a wet cat and made me put both scopes out on the curb. Yes I am whipped but for a very good reason that I won't get into!

author: Chris56000
author_rank: Frequent Contributor
timestamp: April 13, 2018, 02:53:51 pm
content: Hi!Keep the tales coming ladies and gents – they're .asking me feel a bit better already!Any Chain–Reaction Tales of tales of multitudes of surface–mount sparklers, anyone?!Chris Williams

author: Fungus
author_rank: Super Contributor
timestamp: April 13, 2018, 03:12:55 pm
content: What's the most expensive piece of gear anybody's destroyed when a moment's thought could have avoided it?

author: hansibull
author_rank: Regular Contributor
timestamp: April 13, 2018, 04:16:17 pm
content: First day at new job, destroyed the graphics driver on a brand new LeCroy Quantum Data 780. It still works but the colors are all messed up.In order to replace the battery you'll have to remove the LCD panel, which was just a standard 2mm pitch header connector with no keying. An offset by one really did the trick!

author: bob225
author_rank: Frequent Contributor
timestamp: April 13, 2018, 05:53:47 pm
content: Never smoked a piece of test gear, But i did get thrown 4ft backwards and killed £2500 worth of Sony CRT, The smell of burning skin/hair, pcb and dead caps filled the airIt took a week to get rid of the smell out of workshop

author: KD4PBS
author_rank: Contributor
timestamp: April 13, 2018, 06:33:17 pm
content: Not me personally, and not test equipment, but I have in a former life had to repair many pieces of expensive high-end broadcast equipment over the years, typically always due to a TV news videographer who thought he would get the next Edward R. Murrow award. It always went one of a few ways:1) Hurricane or some other extreme weather phenomenon that happens frequently, news photog feels it is best to shoot video right in the middle of the storm instead of from a protected site (typically inside the live truck or the door to the hotel), waterlogging the camera, and doesn't even bother removing the easily-removable battery. $12,000 USD and 40 hours' labor later, the camera is working.2) The news photog feels it's best to not bother bringing the camera back to the shop for the engineer to fix those 99-cent loose handle screws on the camera, so he uses a $1.99 toenail clipper to do it every now and again. As a result, handle separates from camera and ends up dropping into salt water. Doesn't even bother removing the easily-removable battery. $30,000 later for a new camera, lens, and VCR deck, and all is well.3) The news photog is an ace. So much so, he knows how to set the backfocus without a backfocus chart. While camera is on his shoulder. Walking backwards. Down a flight of stairs. In doing so, he ends up turning the lens locking cam instead, and the whole camera and deck slides from his shoulder and tumbles 12 flights of steps down the stairwell. At least he still has the lens in his hand. $15,000 later for almost everything new in and on the camera and VCR, and 120 hours' labor to repair, and all is well.4) The news photog walks away from the camera while it's still on the tripod. In doing so, he trips over the camera power cord, causing the whole assembly to fall square on the lens. Lies about it all stating that the camera "just fell for no reason". Thankfully one of the competitors showed the video proof to his engineer, who showed the video proof to me, who shows the video proof to the news director and general manager. New lens, chassis, and optical prism block and assembly later, along with the 40 hours' labor and $10,000 parts cost, and all is well.What's worse is that none of them ever got called to the table for these kinds of shenanigans.Take my word of advice; no news is good news.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: April 13, 2018, 07:47:54 pm
content: I blew up an oscilloscope in my A-level physics practical exam. I still got grade S1 in the special paper.Still not as good though as when the physics teacher put a 6V battery directly across a galvanometer.The chemistry teachers were the ones out to impress though. They always had a competition on Nov 5th, but I still remember an impressive demo of melting a screwdriver by lying it across the terminals of a car battery...( I'm more careful now its my own personal oscilloscope.).

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: April 13, 2018, 08:03:50 pm
content: Most spectacular demise of a multimeter that I witnessed happened when I was working with traffic signals dept. a long time ago. In a circuit where some low voltage was expected, a swapped connection + a inter-departmental CF resulted in 750V DC streetcar power coming through. If I remember correctly, it was a H&B, but that is a bit hazy. It flashed within such that it shone somehow through the instrument.Inside, it was a black mess.Some years ago, I bought a huge sturdy 4-channel paper recorder. Japanese maker, but I have no record which. When going through the initial testing, the transformer blew. It started with a sizzling noise, then a lot of smoke came out. My flat stank for days.Small Voltcraft experimenters power supply which a friend brought in for test/repair. I was just starting to probe when the main cap blew. I stood in the rain of corrosive fluff while the aluminium cup, which flew away completely, settled noisyly in some corner after it's zigzag journey through the lab.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 13, 2018, 08:47:04 pm
content: while charging an ni cad battery, it overheated, exploded, and left an awful black powder 5 feets around it ( like photocopier ink) was very hard to remove, incrusted ... the first day at my new work lollthe second one in old crt tv's, an 34 inch tube tv, while discharging the tube with an screwdriver connected to ground, my hand had some transpiration, it made an beautiful ark and a small burned hole in my hand while reaching to the ground ...oh almost forgot that one, an friend asked me to check with him a noise coming from a tv, while i was approaching the tv capacitors blown aways up to the roof, my friend and i where lucky, the capacitors passed near my face an his face and lodged into the roof sound isolation tiles, the tv totally died, almost every ic's and transistors blew away.

author: Cerebus
author_rank: Super Contributor
timestamp: April 13, 2018, 09:39:02 pm
content: Quote from: KD4PBS on April 13, 2018, 06:33:17 pmAh, cameramen, ya gotta love 'em. When they're not breaking things they're lining up shots of tits and bums until they the producer shouts at them and gets them back on shot...

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: April 14, 2018, 03:56:04 pm
content: Quote from: Cerebus on April 13, 2018, 09:39:02 pmSomeone has to do documentaries about those small, often overlooked birds and the plight of the homeless!

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: April 15, 2018, 10:38:01 am
content: OK, not test equipment, but I remember many years ago, a friend of my dad's decided he would make himself a variable speed control for his windscreen wipers when such things were very new.He built and installed his circuit, and when he turned it on, the two TO-3 transistors couldn't handle the wiper motor starter current. They both blew, and he ended up with two neat round dents in his car bonnet...

author: CopperCone
author_rank: Super Contributor
timestamp: April 15, 2018, 06:01:38 pm
content: i was probing a broken 30v 30a lambda/xantrax supply and i accidentally bridged a linear regulator, it made a rough noise and blew a fuse.. probably took out half the control board too

author: SeanB
author_rank: Super Contributor
timestamp: April 15, 2018, 07:18:28 pm
content: I saw a Fluke 77 that was Metro electrical issue, returned under "warranty" as it was defective. Probes on this less than a year old meter were best described as ' mostly there, at least the parts near the meter side", as they basically were just burnt wires plugged into the sockets of the meter. Watched as the agents opened the meter, and saw that Fluke had done some interesting shielding inside the case, as it was entirely bright copper coated. PCB had a full complement of parts on it, rotary switch was stuck in voltage measurement, and the LCD came on with random segments on plugging a 9V battery in. However the entire meter from the bottom of the LCD down had not a single copper trace there, all blown clean away, leaving just soldered component pads and bare board with no solder resist where the traces had run. both fuses however were still intact, tested with another meter.Turns out somebody had tried to test the PRIMARY side of a MV distribution transformer, and that, for some reason, the meter did not really like having, as Dave so eloquently says, having 11kV, at a source impedance of practically Bugger All, shoved up it's clacker. No word as to if the primary fuses or the substation trips operated, or if they were ever able to remove the remains of the probe tips from the bolts either. Hopefully no Darwin award either.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: April 15, 2018, 08:07:14 pm
content: Most expensive to date: PM3323.I apparently managed to damage one of the P2CCD-Chips when I tried to repair it (see my PM3323-Thread for more details). The result is an unrepairable scope that is taking up space here while I'm figuring out if I should try to emulate the function of the P2CCD Chip that is unobtainable, has no datasheet anywhere on the net, and is an SMD-component (rather hard to make a interface between a replacement built on a PCB and the old footprint).About 150€ worth of magic smoke in this case. And the lesson to stay away from nasty ceramic chips that are prone to breakingBtw. anyone here who want's the scope for parts?

author: najrao
author_rank: Regular Contributor
timestamp: October 26, 2018, 12:58:27 pm
content: This happened in our testing shop, which has a 400V 3phase 1500kVA feed. Noticing an iron crowbar(?) sitting on a ledge about a foot above live oil circuit breaker terminals, I admonished the test engineer for such recklessness, and told him to take a shutdown to remove the offending metal bar. Minutes later, there was a huge explosion, and a creature emerged on all fours, covered in black soot all over. He had tried to remove the crowbar, and promptly dropped it on the M36 copper stud terminals. His injuries needed 6 months of intensive care, and left him scarred for life.

author: Zucca
author_rank: Unknown
timestamp: October 26, 2018, 01:20:53 pm
content: I got yesterday some holy smokes events playing with Li ion cells. I did not damage the cells.Li ion cells are scary, if you do a mistake on building the battery pack, there is no way to turn them off... you have to watch them smoke and die until the energy is dissipated.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 26, 2018, 01:35:41 pm
content: Along that line...In the US utilities use an electrical meter that plugs into a socket. The line (supply) terminals are the top 2, the load (house) are the bottom 2. I was building a house and before the utilities put in the meter one of the contractors sent out an HVAC tech to do a trial run on the heating plant. Well, he needs power for that, so he goes to install shorting bars on the meter socket - HORIZONTALLY. (he's using one of those sliding metal fasteners they use to clinch ductwork together and when you bend tabs on it, that's the only way it will fit, right?) The first one across the bottom is fine, the second vaporizes instantly with a loud bang and flash.The tech survived with no injuries, but left soon after without doing his test.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 26, 2018, 01:38:59 pm
content: Anyone who has not witnessed a large, shunt-field DC motor lose its field and spool up until self destruction, has *not yet seen* a catastrophic failure.On a shop I worked many years ago, we assembled large industrial controls...all low voltage <600 V, but large power.We were delivering a 100 HP motor and its controller, and were in the final testing stages, and everything was metered up.One of the critical tests was to ensure that the field loss detection circuit was indeed functional, where one deliberately removes the field excitation. Mind you, this test is done with the armature fully disconnected. You remove the field, and listen for the main contactor releasing.So....this technician decided to cut the field wire. With the motor running at full armature voltage. Unfortunately for him and everyone else, the motor was sitting right next to the control panel where the red emergency stop button was located. You don't want to be near a large motor self destructing by the centrifugal forces.Someone had to run to the building's main breaker panel, to shut off the main breaker.Of course, this large motor was ruined. So were several pieces of equipment, including our brand new Tek scope which had been hit by shrapnel.

author: Berni
author_rank: Super Contributor
timestamp: October 29, 2018, 06:32:35 am
content: Now that motor mishap must have been quite the scene. What gets torn off it anyway? I would think that most of the rotor chunks would get caught by the stator around it so its things like the cooling fan exploding from the forces?

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 29, 2018, 01:27:29 pm
content: Yes, the cooling fan starts disintegrating first.The brushes and commutator suffer also significant damageSo far, things can be repaired.....but when the unbalanced rotor spinning at a freaking speed hits the field poles, then the thing is damaged for good.

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 29, 2018, 05:03:08 pm
content: I didn't witness this, but it was a legend around the EE lab at school. One of the then-current professors had worked with 3-phase generators at a new power plant. These things were built like, bigger than, and probably stronger than, the proverbial tank; if you've seen one, you will get the picture. One of the jobs during new construction involved spinning up a generator and connecting it to the main buss to bring it online. In the olden days, synchronization was done by a set of 3 bulbs wired between the generator and the power buss, such that when the lights all went out there was no voltage differential and the generator could be safely switched in. It's not clear exactly how it happened, but the indicator was mis-wired such that it's display was 180° out of phase with the actual voltage. The operator carefully synced the lights, threw the switch, and...The best description which came down of that event was that there was a hellacious screeching noise, and the generator ripped itself free of the floor mountings and rolled over. Most of the participants were fleeing in terror at that point, so further descriptions were vague.One that I personally was involved with? OK. The school's power lab had a lot of very burly motor and generator equipment, which was used to train power engineers in 3-phase systems. A friend and I were hanging out before a class, and trying to make sense of some of the things we were learning. We had a heated discussion about the differences between 3-phase delta and wye systems, where the delta had a system neutral connection. He insisted that in the same distribution block, the neutrals of both systems came from a common source, should both be near ground potential and could be safely connected together (the power leads, of course, should be left isolated). I felt that was naïve, but couldn't refute his argument without further knowledge of how the secondaries were wired.Sitting right next to us was the distribution panel for the lab's 3-phase power, with both a delta and a wye setup. I suggested, somewhat humorously, that if he was so sure he could just plug the neutrals together right there and prove it! He noted that there were circuit breakers for both systems - just run a big cable between the neutral sockets and flip the breaker, right? If there was current flow the breaker would pop and that would be it. So we switched off the breakers, ran the cable, and I insisted my friend be the one to flip the breakers on since he was SO certain.I don't know exactly where the big BOOM came from (no, not from the lab where we were), but the lab and most of that wing of the building went dark. My friend, eyes as big as saucers, yanked the cable out and flung it into the box where the cables were stored. People came boiling out of the classrooms nearby, in a panic because the rooms had all lost power - and most of them had no windows. I thought we were going to be in big trouble, but thankfully no one seemed to connect us with the event. The professors were running around checking all the breaker panels, and finally found all the right ones to bring power back. It astonished both of us that a test panel, clearly used for high power experiments, affected so many essential circuits - I would have expected it to be split off near the incoming circuits out at the power drop. Perhaps the ground currents were so unbalanced that all the other breakers saw significant excess current?There was no apparent damage, either, despite a significant number of circuits popping their breakers and lots of sensitive test equipment being run in the area. But no one who was in the EE department that day will forget the incident!

author: Berni
author_rank: Super Contributor
timestamp: October 29, 2018, 07:20:59 pm
content: I was told in uni about really bad thing happening if you don't synchronize the generator before connecting it to the grid, but they ware never all that specific on what exactly would happen. I did imagine something mechanical would break and grind to a halt and fuses would blow, but i didn't think one of these massive generators would fling themselves across the room!And yes we also managed to knock out the power on an entire hall in school when a schoolmate wired up some contactors for star and delta switching of a motor. There is the usual procedure of first powering it up with big powerful incandescent lamps in series with all phases so that a short circuit just lights them up. It passed that check but then it was tested with the lamps bypassed. Motor started up fine in star but then when it was switched into delta the contractors for star did not open while the delta contractors closed, effectively shorting all three phases in a bang while everything went dark. The short did trip the breakers in the classrooms distribution box as it should but it also tripped the bigger ones for the whole hall. This could be because there ware classrooms full of PCs in that hall that likley put a significant load on it while the fault current on top of it convinced the big breakers to trip too. The school had its own transformer substation inside the building the short cable runs provided lots of peak current capability in a fault.

author: HerbTarlek
author_rank: Contributor
timestamp: October 30, 2018, 03:20:45 am
content: Quote from: GregDunn on October 29, 2018, 05:03:08 pmPetition to change the thread name to "I don't know exactly where the big BOOM came from: Test (and Other) Equipment Disasters!

author: BradC
author_rank: Super Contributor
timestamp: October 30, 2018, 07:20:11 am
content: Quote from: GregDunn on October 29, 2018, 05:03:08 pmI have a photo somewhere (that I have been persistently unable to find) that was given to me by a grizzled old gentleman of an event that occurred well before I was born. It was a beaut photo of a small power house with a generator sized hole in the wall and the remains of a generator and its turbine sitting on the ground outside. Reputedly another 180deg out of phase event.That's 3 massively destructive ones I've heard of over the years, so they're probably not as uncommon as one might think. They do seem to get hushed up though.My old man tells one when he was a junior power engineer. One of the guys in the class synced up the demo motor/generator set out of phase and knocked out the power for about 4 blocks in East Perth back in the 60's. Apparently damage to the generator and some upstream popped breakers, but nothing left the floor.The worst (most expensive) I've done is poked 240V into the USB port of a very expensive laptop. I have melted a screwdriver on a battery, but while spectacular nothing exploded.I also vote the thread title change proposed above : "I don't know exactly where the big BOOM came from: Test (and Other) Equipment Disasters!".

author: vk6zgo
author_rank: Super Contributor
timestamp: October 30, 2018, 01:55:31 pm
content: Nothing quite so disastrous as some of the previous posters, but I have experienced a few of these.Imagine, if you will, a large attended Radio Station, just after lunch in the mid 1960s, with the Boss playing cribbage with a couple of cronies in the Lunchroom.The rest of us took the time to study, work on "foreigners" (private jobs), or to meander through some of the less strenuous daily routines.A Cadet Engineer had, as his project, to test the low voltage characteristics of some silicon HT rectifiersbeing considered as replacements for the existing mercury vapour rectifiers.He needed a high current low voltage supply, so a lead acid cell suggested itself.The 24 volt diesel start battery consisted of a lot of individual cells all connected in series, so off he went, trailed by a Technician in Training holding an Avometer, some wander leads, a couple of big resistors for a load, & clipboard for writing down the results.The Cadet EE decided to slightly loosen the two terminals on a cell, then quickly connect his test set up.He grabbed his "crescent spanner" (adjustable wrench) & set to.As these things are wont to, the spanner slipped & shorted the two terminals of the cell.The rest of us heard a resounding bang, & appeared out of our various workshops, offices, etc, rather in the manner of ants from a disturbed nest.We were confronted by an ashen faced, but otherwise unharmed "Ginger Beer" & a battery case with a gaping hole where the guts had been.His "offsider" was also OK, having leapt backwards over the protruding exciter on the big alternators.The Boss "did his block" --- there was steam coming out of his ears, whilst the forlorn perpetrator cowered.We ran with one less cell for a few days, & everything seemed to work OK.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 30, 2018, 02:07:53 pm
content: Thankfully all these accidents related so far, did not cause any human tragedy, and thus can be told as a funny experience.There have been some other electrical accidents which have indeed caused injury or even death. Youtube has several very scary videos of switchboard faults.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 30, 2018, 02:35:41 pm
content: But wait, there's more!24 volts from the aforesaid battery bank were reticulated around the building .There were a number of alarm systems, & so on,which required -24 volts, which was normally provided by a Mains powered supply.When Mains power was lost, these alarms, etc, would automatically switch to the battery.Yours Truly was told to replace the electrolytic capacitors on this supply, as they were a bit "long in the tooth".I duly turned the supply off, the battery took up the job, so I pulled the thing out, & made a nice, neat job offitting the new ones .I turned it on----BANG!! followed by what looked like a snowstorm in the Control Room.Yep! electros back to front!---forgot it was a -24volt supply!Many years later, at a different employer, a Trainee came to me so I could check his construction of a "Dick Smith" kit he was building for a work application.A cursory look showed "all good", electrolytically all polarised as per the PCB, etc.He turned it on & BANG!That's right! Dick Smith had got the PCB labelling wrong!Going back in time, at my first employer, we had some tube radio chassis left over from a long finished run of mono "Radiograms".My job was to test them prior to them being put out on special.To this end, I grabbed a big 12" Rola loudspeaker, & looked at the radio to see where the speaker connected.All I could see was a length of "figure 8" cable coming out through a grommet on the side of the chassis."Aha!" Thought I, connected it up to the "12OX" speaker, & turned the radio on.There was a sound like a rifle shot, & the voice coil was no more.Turns out the length of "figure 8" was Mains to power a record player, so it could be turned off with the radio "on/off"switch.Strangely, the speaker looked quite intact, apart from the open circuit voice coilThe Boss didn't get as angry as I thought he would, so I still had my job

author: Chris56000
author_rank: Frequent Contributor
timestamp: October 30, 2018, 07:53:30 pm
content: Hi!Mods, I'm more than happy to have the Thread Title changed to "I don't know where the big "BOOM!!!!" came from as that's been the story of my life in over thirty years of assorted fixings!!Please keep the tales coming everyone!!Chris Williams

author: tautech
author_rank: Super Contributor
timestamp: October 30, 2018, 08:00:51 pm
content: Quote from: Chris56000 on October 30, 2018, 07:53:30 pmYou don't need Mods help, just edit the OP yourself !

author: najrao
author_rank: Regular Contributor
timestamp: October 31, 2018, 09:16:21 am
content: I too have seen a 110kW 2000rpm dc motor suddenly lose its field winding feed. But i was near enough to a KILL ALL button to stop it in its tracks quickly. It coasted down in several minutes from the high speed. Nothing broke.Was doing a dead shorting oscillograph test on a 125kVA generator coupled to a dc motor. The cast iron coupling halves were 14" dia and weighed more than 50kg each. When my assistant closed the shorting 600A oil switch for the umpteenth time, something whizzed past my ear, crashed on to shop window some 60 feet away, took the steel window with it and deposited it and self a hundred feet away in the yard. Yes, it was half of a coupling half! Coupling guards became compulsory after. Eye wash ones, I am afraid: were made of 2.0 sheet metal.

author: Brumby
author_rank: Unknown
timestamp: October 31, 2018, 09:40:25 am
content: Quote from: tautech on October 30, 2018, 08:00:51 pmYES! Just go to the original post, hit "Modify" and then pop up to the subject line and change it yourself.

author: Fludo
author_rank: Regular Contributor
timestamp: October 31, 2018, 12:20:00 pm
content: We had a 3 phase 110kVA variac that we used to transform the shop 440 down to various voltages during testing. It was a really large unit, about the size of a refrigerator. The device was ordered with a Wye connected input, but for some reason the engineers connected it as a delta and operated it no problem for 2 years before my time. They had issues with the variac blowing the main 200A circuit breaker and shutting down 1/4 of the machinery on the shop floor, but attributed to a "tired old breaker" and simply moved the device to a different branch. Meanwhile, I called the vendor and he stated that the inrush current peaks at 900A, and the proper startup procedure was to buy a bigger variac to slowly ramp up the voltage on the 110kVA unit, to avoid inrush....We had a request from another department to troubleshoot a 120VAC 3 phase power supply, and this variac was the only available source of power. For good measure, the output was fused at 30A per phase as the person requesting help was a known idiot who always managed to leave a wake of destruction in his path. After juicing the variac, a single output fuse blew but the variac remained operating, creating an imbalanced load with no neutral as a return. The supply tested was faulty and had apparently destroyed other power sources(much more expensive) around the plant.After that incident the variac had one phase 40V lower than the other 2 and the device, and I was called down from the office to troubleshoot. Removing the cover to the enclosure showed no signs of damage, but after measuring continuity for each coil we found that one had significantly lower resistance than the other. It was only after we called the vendor requesting service that he reminded us that the variac was Wye input, and stated very clearly that it was in the orignal quote and on the nameplate. He also mentioned that several fires occurred because people often made the same mistake.Moral of the story:Trust nobodyMake sure you read the name plate

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 31, 2018, 03:05:07 pm
content: Fludo:3. RTFM!Every Lab has its own ISO9000-certified idiot.In a lab for a power supply company I used to work for, we had to make sure "universal input" units met specs both at 120V/ 60Hz and 230V/ 50Hz. As such, the lab was equipped with both North America and European type outlets. Foolproof enough? Not quite for a certified idiot.We had some 120v only units that he required to test. He went to this particular bench, where the US-outlet had something plugged already, and only the European-outlet was available.You guess what happened next. He found an European to US plug converter, and proceeded to sequentially plug a total of 30 units, one after another, and blow the fuse on every single one of them.The units like most power supply nowadays, had a non-user replaceable fuse. Which meant that every single one had to be reworked.This guy, in another occasion, also connected an array of 12VDC fans to 120VAC.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 31, 2018, 03:37:18 pm
content: At university our electrical machines lab was always source of several interesting events, ranging from a yellow glowing 200W variable resistor to blown bakelite ammeters. Each bench had several outlets and, for good measure, they were fitted with 2A glass fuses all around - the replacement rate used to be at least a dozen each class. Anyhow, the most interesting event was not electrically related, but mechanical: one of our colleagues was running a motor/dynamo combination and everything was going great, but some of the meters were behind the machines and we had to stretch ourselves over the running set to take the readings. Well, this colleague was using a loose shirt, which was caught by the axle and started to rip his shirt out. Fortunately someone else was able to cut the power of the bench before injuries happened. We had a good laugh.On another occasion I needed ~300VDCand, given our outlets were 220VAC, what could possibly go wrong by simply fitting a full wave bridge rectifier directly on the outlet? After borrowing four 1N4007 from the lab inventory and a hefty capacitor, I set out to solder everything to a universal board and properly isolate everything. When I plugged the circuit to the outlet on the wall, there was a loud BANG and two of the 1N4007 diodes vapourized. By elimination I realized that one of the 1N4007 diodes was shorted (damn students that blow up devices but are too afraid and return them to the inventory).Anyhow, I set out to the inventory parts bin again and got two more 1N4007 diodes. This time they were looking quite new and the chances of a second diode being shorted are zero, right? Right? RIGHT? Well, one thing lead to another and the second BANG proved too much for the poor wire: the plug was still in my hands but the wire had been pushed back towards me - no breakers were opened as the wire had become the fuse. Anyhow, I ended up finishing this another day as my friend was cursing me for the scare I gave him twice.

author: 0culus
author_rank: Super Contributor
timestamp: November 01, 2018, 05:11:20 pm
content: Some of the stories in this thread are just crazy...I fortunately have never personally done a "Big Boom" (yet). But when I was reading up on multimeter safety a while back, I came across a story (that of course I cannot find now) about someone deciding it would be a good idea to connect a Fluke multimeter across test points on some kV class equipment at a mine, if I recall correctly. Wasn't much multimeter left, as it was massively above the 8 kV pulse rating that they state on the back of the meter. Perhaps someone remembers this or a similar story?

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 01, 2018, 05:23:31 pm
content: There is a Youtube video which describes a very similar accident on a paper mill, if I recall correctly.Unfortunately there was a casualty on this instance, and the people who witnessed the accident mention on the video that the poor guy was essentially on fire.The strange thing about this particular accident is that the deceased was a *very experienced* and certified electrician. Overconfidence, perhaps? We'll never know.

author: 0culus
author_rank: Super Contributor
timestamp: November 01, 2018, 11:04:22 pm
content: Quote from: schmitt trigger on November 01, 2018, 05:23:31 pmDamn. That's sad. Complacency is dangerous though.

author: bd139
author_rank: Super Contributor
timestamp: November 02, 2018, 12:01:55 am
content: Had a near miss a couple of days ago. This is in the TEA thread but I thought I'd repeat it here.Getting a bit tired and dropped a scope probe into the live power supply on scope. Flipping loud crack like you've never heard before as one of the caps emptied through the probe, into my TDS210 and back out of the other probe to ground in the scope. Sounded like a firework going off. One dead DUT! Fortunately the TDS210 survived that little incident unharmed.My nice new Tek probe had a nice burn on itHowever fortunately this wasn't a total disaster. Just blew the line fuse but I spent half an hour testing all the rectifiers and transformer taps to make sure I hadn't properly screwed stuff up.But poo nearly came out of me as it was a not too shabby Tek 250MHz 475A with DM44 I thought I had buggered completely for a few minutes.Resulting lesson:No less than a week before this I smoked some nice Pomona leads by being lazy and using black for positive because it was the nearest thing to my hand... That made a not insignificant fire and stank the place out for about 5 hours

author: Brumby
author_rank: Unknown
timestamp: November 02, 2018, 01:08:46 am
content: Quote from: bd139 on November 02, 2018, 12:01:55 amI get really uneasy when I don't have a lead of an appropriate colour at hand, especially for power connections, for exactly this sort of possibility. As a result, if I use an "alternative" colour, I will keep to cool colours for negative and warm colours for positive. Once I did use a black lead for power - but I put a loose knot in the end to remind me it was "knot" what the colour suggested. Even then, that was easy to mistake for a cable that just had a loop in it and I wasn't comfortable.

author: Apollyon25_
author_rank: Regular Contributor
timestamp: November 02, 2018, 02:16:24 am
content: My first day at a new job began rather innocently when I was asked to test a large variable speed drive (in the test area) before taking it into the power lab and wiring it up to do a specific test. All the precursor low energy tests went well so I flicked the 3ph ON switch. BANG. (These retailed for about $150k) I sheepishly went back into the office to an eruption of applause...Same company several months later, a colleague and I were testing an inside-delta configuration on two of the largest drives we made (at the time), we paper-scissors-rocked for the turn-on honours, and as I threw the switch, the inrush bounced the cables in the overhead tray, dislodging a ~1m length of wood that had been thrown up there...Same company... during the testing of an overspeed algorithm the large, test motor's rotor expanded out and hit it's stator, ripping the motor out, and rolling it across the floor, dragging the VSD off the bench, and leaving us holding the test box (on/off switch and a speed pot) with some dangling wires...Same company (boy we had some good times there!) - a new staff member had made up a 240Vac mains powered board, and was probing it. I suggested that he may want to tape up the mains connections so he didn't kill himself. I go back to find he had used packing tape. I suggested that he perhaps use some nomex sheet and some insulation tape instead (both readily available in our lab) as any pressure would simply puncture through that tape... He nodded at me, and proceeded to ignore me.Literally, as I sat back down at my desk, I hear him yelling, and trying to shake the mains wire spike out of his finger, while being electrocuted. At that point, I became incapable of rendering assistance, instead laughing my proverbial off. A colleague, also watching the previous exchange, manages to compose himself just long enough to hit the emergency stop button...And now I think about it, I have a bunch more...

author: GregDunn
author_rank: Frequent Contributor
timestamp: November 02, 2018, 02:30:34 am
content: Quote from: Brumby on November 02, 2018, 01:08:46 amSame idea I had - I have some test leads which are yellow and blue which are handy when I already have red/black ones connected to a circuit. No chance of confusing them at either end.

author: bd139
author_rank: Super Contributor
timestamp: November 02, 2018, 07:55:26 am
content: I just bought a few more red and black ones and persuaded myself that I need to be less lazy.Mid project my bench looks like Jim Williams and Bob Pease had a hacking session on it which doesn’t help. Need to be more organised.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 02, 2018, 02:04:10 pm
content: Don't forget the small silly mistakes......Back when single sided, thru hole boards were the norm, jumpers were extensively used.In large operations jumper-wire insertion machines were used, to avoid slowing down the component sequencer and auto insertion machines.I burned my fingers when someone attached to a spool of wire with some 63/37 solder labels. Nice prank for a newbie!Had also a couple of large electrolytics blow because they were installed backwards. Your clothes would stink for hours.

author: HKJ
author_rank: Super Contributor
timestamp: November 02, 2018, 02:34:33 pm
content: Quote from: schmitt trigger on November 02, 2018, 02:04:10 pmWhen you have both solder and that type of wire on your bench it is easy to pick the wrong one. I have sometimes had some "solder" that would not melt, but got very hot to hold

author: vk6zgo
author_rank: Super Contributor
timestamp: November 03, 2018, 02:05:06 am
content: Quote from: HKJ on November 02, 2018, 02:34:33 pmIt was a common trick to very carefully solder a length of "tinned copper wire" into a section of solder, then wind it back onto the solder spool, & wait for some busy person to get caught out.I've caughtmyselfout with nastier things.(Maybe it was Karma for doing the trick described above).I was trying to patch up a rusty old car by welding new sections of metal in with an oxy acetylene torch.A problem is, that it is easy to pick up the rod by the end you've just used( the hot end).A magazine suggested bending a hook on the cold end, so you would always know which was which.It worked well, until one time, I absent-mindedly picked up the rod by the centre portion.The "hook" became caught up under the car wheel arch, so I heaved , it came free, & my hand swung through the "outer envelope" of the gas flame!Ouch!!!, Super Ouch!!!

author: Cerebus
author_rank: Super Contributor
timestamp: November 03, 2018, 11:23:32 am
content: One presumes youwerewearing welding gloves, or your handle on here would be some variation on "hooky".

author: vk6zgo
author_rank: Super Contributor
timestamp: November 04, 2018, 02:04:21 am
content: Quote from: Cerebus on November 03, 2018, 11:23:32 amNope!Just very sore like abadscald from hot water, but a lot more localised.Hurt like mad, made me swear a lot, but that's it.Not many DIY prople doing gas welding use gloves, as they are too unwieldy--- cutting, or arc welding, yes!

author: 0culus
author_rank: Super Contributor
timestamp: November 05, 2018, 02:56:22 am
content: This thread would not be complete without this: