Before an important demo, the power supply engineer was nervous. Really nervous.
In early 1980s, I was a member of a team working on a nuclear magnetic resonance system, which required a very stable 100V 10A power supply for the magnetic field.
The stability requirement was a tough ~1ppm of noise and hum, and my colleague who was designing the power supply built a coarse 3-phase thyristor regulation, followed by a smoothing linear regulator.
To his big disappointment, those thyristors, even when abundantly over-dimensioned, kept misfiring, and the high inrush current into a large capacitor bank kept melting the semiconductors down, and causing in turn a short on the 3-phase mains, triggering the automatic circuit breakers, both on the PS rack, and the main ones, shutting the whole department off. It was happening several times a week, so it soon became rather annoying.
Finally to everyone's relief, my colleague has managed to reduce that inrush current, and also obtained some 70A rated thyristors, which cured the problem.
As the delivery day of the NMR system approached, we invited a professional photographer to take pictures for the documentation, and that's where I got my bad idea...
Demo day arrives
On the day before the demonstration for our customer, we were all busy with the last checks and preparations, and the PS designer was naturally rather nervous himself, he was sitting by the PS and an oscilloscope with the probe attached to the output voltage, the input AC coupled and the sensitivity maximized to show the line ripple, fine- tuning some trimpots, and watching carefully the changes on the output waveform.
I approached quietly behind him, with a photographic flash light fully charged, and as he reached once again for one of the trimpots I pressed the flash button. The flash light fired with a silent "PUFF".
For a few microseconds the time stood still. Then as in a slow-motion my colleague jumped up, the screwdriver which he was using to adjust the trimpots went left, the chair flew backwards, his glasses to the right and as he was falling on the floor he reached for the power switch and pulled it down.
The room burst into laughter.
After we all calmed down again my boss approached me and told me that my little joke could have had some very serious consequences if, by chance, my colleague dropped the screwdriver into the PS.
"I know, boss," I said, "so I gave him my plastic screwdriver last week!"
Once when I was at tech college, we were looking at a 1kW transmitter. My friend and I hid behind it (it was a full rack unit with some nice big bottles in it). He lit a cigarette and blew some smoke through from the back. I waited a bit - till the smoke would have been wafting out the front - and then banged the side of the cabinet. Our instructor shut down the transmitter's main power supply pronto. He had a bit of a sense of humour failure and I don't think ever really forgave us, though he did see the funny side of it a bit later. I realised that that it is best to pull these stunts on your colleagues or equals, not your boss or instructor.....
Once when I was an electronics tech fixing pro-audio gear, I was deep into troubleshooting a power supply on a tape deck, when my boss, ever the prankster, rolled his chair over a sheet of bubble wrap. Thought I fried the whole supply and it took quite a while for my heart rate to return to normal.
This reminds me off our boss and sales and marketing department. We did many projects for US DoD and after sending First Article (FA), we at Engineering and Design department eagerly await customer feedback. Many a time my boss and sales people play possum and give us wrong feedback that there is problem in FA and is coming back or order may get cancelled. The concern engineer is so worried for few days or hours and eventually they tell the truth. By this time, they take out some improtant information from us or has got some realy low price for engineering job.
I was working on a bench that looked through the risers on my bench and the one facing my bench towards a third bench where the other hardware design engineer was bringing up an offline smps. There had been had a few small explosions of the power switch as the unite was being tested under high line conditions. I had received a new part packed in large bubble wrap. Not intending to cause a ruckus but just because it is fun to role the stuff up and twist it to pop several bubbles at once, I did. I did not know the guy working on the supply was just turning it on as I gave the first big twist with several loud pops. That guy must have jumped nearly a meter in the air and slammed the switch off. Seeing him jump like that I walked around the bench to see him shaking like a leaf. I apologized and he told me that he was just turning the thing on at high line when the bubbles popped. He went out and smoked a few cigarettes before returning to work. On the next power cycle his supply did emit it's own rather loud report again. I eventually took over that project and that supply is now employed world wide. Even in Russia where the power can swing between 190 and 300VAC!
Back in the 70's I curiously watched as a technician merrily was twisting together a bunch of 4.7 ohm 1 watt resistors together while across the lab another design group was about to power up a several hundred watt switching power supply for the first time. The dynamics of switching power supply design back in the 70's meant there was quite a bit of trepidation during First Turn-On. Meanwhile, our tech had hooked this string of resistors up to a variable transformer connected to the AC line and place them in front of a computer fan. As they started up the power supply, He turned up the voltage just enough to make the resistors began to sweat. After about a minute a very faint wiff of "O' de Ohm" made it across the room, and suddenly we hear "SHUT IT DOWN! SHUT IT DOWN !". I made it a point to not stand to close to the chuckling tech as these miffed engineers turned around and glared.
Thinking back, I wonder sometimes if I was just an irresponsible idiot at times. Maybe i was, but it now seems that my distorted sense of humor is shared by a large number of excellent engineers. I'm relieved to discover that. Thank you all.
Joshua...there's a saying that's very relevant here.
"It's never too late to have a happy childhood"
Which is I think what most of us were doing when we got up to these pranks. In most cases they did no long term harm to anyone or anything.
As you've observed, Engineers by and large have a good sense of humour (sorry, humor to you!)and often the jokes are appreciated as much by the "jokees" as the joker. I don't think it's irresponsible, jsut makes work more fun.
David, in my opinion engineering is by an large very humorless profession and i attribute it to the dangerous nature of the practical joke. Working with high current, voltages, heavy equipment etc need very careful handling otherwise disasters are just round the corners.
Sounds like you've been working with the wrong guys Himanshu!!
Yep, we sometimes work with dangerous stuff but how often do you hear of a practical joke going really wrong? I think most engineers know how far to go without putting someone in danger.
Hence the last line of the post:
"I know, boss," I said, "so I gave him my plastic screwdriver last week!"
Erik, was that the truth or was that just quick thinking on your part?
I agree with you David, as long as there is a measure of safety first displayed by the prankster, all is fun and is fair game, as far as I am concerned.
We have placed electrolytic caps in reverse (in purpose) for a technician to debug, and the moment of power-up is priceless for those in the know.
Once a colleague was repairing a measurement unit a customer nearly ruined. It took all morning and he was cursing a lot. He was really annoying.
When he was sure the repair was finished, he left for lunch.
In the mean time we placed a 0207 resistor underneath the unit, which was housed in a 19" 21 TE cabinet, wired it to a power supply well hidden on the next desk and adjusted the voltage. When our colleague returned, he continued - trying to bring the unit into service again.
You might imagine his reaction when he switched the unit on and - as the "auxiliary power supply" was activated at the same moment - a thin trail of smoke escaped from the overhauled unit. That was the time we defined new classes of parts: LET = Light Emitting Transistor, SER = Smoke Emitting Resistor, LER = LE Resistor (use a bit more power and you can remove the coating and watch the metal film glow).
Years ago I was working on the B1 bomber gyro platform and I was using a number of fans to cool the electronics box. One night another engineer brought a big blower to the empty bench next to mine and plugged it into the same outlet that ran the box. He had filled it with chad, little punches of paper from card stock used to program an old HP computer. The next morning, I turned the box on and instantly my world was filled with blown chad. I immediately shut it down and everyone thought it was pretty funny. It took me a half day to clean it up.
Then, I noticed that only a small part of the huge pile of chad actually blew out. Plotting revenge, early on Thursday afternoon I returned the blower to him, placing it on the empty bench next to his. He made some comment about any left over chad but I smiled and mentioned that he had no worries as it was all over at my bench. That brought about another round of good laughter.
I came in on Friday morning around 5 am. I plugged it into his bench and covered the power cord with some of the piles of papers on his desk. I also placed two "decoy" power cords next to the blower, thinking he might unplug them first.
True to form, at 8 am he turned on his bench and his world was filled with chad. What was even funnier, is that he didn't figure it out at first. Then when he did, he kept unplugging the wrong cords to shut down the blower. By the time he got the blower off, all of the chad was all over his desk. We both were called into the engineering manager's office and got a lecture on that one.
This joke was quite a bit louder and much more exciting, but not very funny. I was working with an electrician and we were in a utilities closet, which was behind a janitors closet, all concrete walls and ceiling. What we did not know was that as a gag, I guess, somebody had dropped some pieces of #10 bare copper wire into the conduit that fed the 3-phase 480 volt power to the main breaker in the panel we were looking at. When the electrician pushed on one wire to get a better view of the terminals, the chunk of #10 wire fell down across all 3 phases, and instantly evaporated, with considerable flash and bang. The acoustics in the small volume made the sound even louder. We never did figure out just who or when the trap was set, which is very fortunate for whoever did it. It was not very funny.
Years later I worked with another electrician who thought that it was quite funny to tie all three phases of the feed to a large motor, downstream of the starter contactor, together with about #20 wire, and then have the engineer, (me), see if I could spot the trouble when they went to start the 75 HP motor. Those watching were dismayed when I was not amused.
As per previous comments, playing jokes like this with 3-phase mains power is neither funny nor clever. The flash from evaporating copper wire can cause serious injury. You can get just as good results without such dangerous practices.
When I was in school in the late 60's, We would have to build up circuits on a proto board, and hook up a bench supply.
Several times we concealed old-fashioned photographic flash bulbs in the protoboards, and wired them to the power. When the victim flipped on the power supply toggle switch to start work they were greeted with a huge flash and pop.
I also remember removing and reversing the cardboard sleeve on foil capacitors. The victim would then not know that they had wired the capacitor in revese polarity. When powered-up this would produce an startling explosion. Sometimes it would un-roll the capacitor.
In high school we had an electronics program. The classes were taught in a detached "trailer" that had its own electrical service. The service was located in the back of the trailer; first one there got to walk in the dark to the back and flip on the breaker. There were desks in the middle facing the board, with electronics stations lining the sides. These held a scope, DVM and bench power supply. One day I decided it would be funny to wire small electrolytics (1uF) across all the power supplies backwards and turn the supply on with the main breaker off. Whoever got there first would turn the breaker on and before they got to the front of the room the caps would be exploding. Well, it was the teacher that got there first, and once everything settled down he was not happy. A "little" joke got out of hand when someone decided if a small cap was good, a bigger one would be better. They did the sme thing but with something like 4700uF. The unreal mess was not expected, and someone could have got very hurt (ok, I know, you could get hurt from little ones as well, but I was a kid). After that anyone doing it would be expelled. That was also the class were we decided wiring a sign transformer (15kV) to the handle on the door was funny as well...
Here's one some of you may recognize: In the old days before test equipment had data storage and file I/O, we used to do data collection with Polaroid cameras that nicely fit over the display of the scope or spectrum analyzer.
The Polaroid film needed to be coated to preserve the image, and each film pack came with a plastic tube containing a squeegee full of the coating goo. The cap on that plastic tube made a very tight seal.
The plastic tube, filled with dry ice, capped and casually dropped into the victim's lab coat pocket would eventually warm up and the CO2 pressure would blow the cap off with a loud popping noise :)
When my roommate and I were working at NOAA during college, his boss was ready to play a joke on him. He had a new circuit built, an o-scope ready to test, and his back to the hallway. His boss walked up behind him with a tall, empty metal trash can that he was going to drop when the probe first touched the circuit. Unfortunately for my roommate, he had a hot AC line where there was supposed to be a low-voltage signal. The probe flashed and self-destructed, and his boss never got the chance to drop the can. An orignal ROFL followed.
January 2016 Cartoon Caption ContestBob's punishment for missing his deadline was to be tied to his chair tantalizingly close to a disconnected cable, with one hand superglued to his desk and another to his chin, while the pages from his wall calendar were slowly torn away.122 comments