Your stupidest mistakes

[peteb2]

Going back to the days i'd a father-in-law, i watched in awe one arvo as he single handedly... survived electrocuting himself.

Here in NZ we have the same mains plugs as Aussy:



"Dad's" biggest hobby was his 20ft speedboat that he used purely for fishing and much of it he had built or modified. This included the crazy rear facing 'trailer' board for use during towing. It sat width-wise across the upper part of the boat and carried the rear running lights, brakes, turn indicators plus illumination for the license plate. "Dad" had wired the whole thing himself but i was not happy he had used mains plugs and sockets everywhere! I argued for weeks he needed proper automotive stuff and never to use mains connectors for anything else because muckups can happen. Stubborn old fart, knew better though.

In the getup had 2 short length plug to plug (known as suicide lead) and a socket to socket 'jumpers' that joined (plugged into) into what was a backbone loom that would be run out from the rear of the towing vehicle hitch point and then connected plug/sockets on the board to power the lights.

OK it worked well enough.

Oneday 'Dad' was on another project, ran out his longest mains extension cord to the back garden that needed him to use the old skill-saw. That lead wasn't long enough so he then unrolled his 2nd longest extension only he ran it the wrong way round so he ended up with it's plug where the socket needed to be. No problem, the boat was sitting there on the trailer so he grabbed the two 'death leads' and adapted the ends of his 2nd extension lead.

Then he picked up the skilly only to be thrown off his feet, and hurl it into the air plus yell a whole lot of obscene words. His trailer adapter leads put mains Active onto the body of the crusty shinny old alloy body of the saw. No amount of protest on my part made him chuck the entire setup away and rerun the 2nd extension lead. The obnoxious old fool simply set about changing the wires to which pins in his death leads. He just would not listen to me... a friking electronics tech at the time!

Funny thing though.... Next time he went out with the boat the wrong lamps came on and he couldn't work out why!

[steaky1212]

The top of the stairs featured a perfect spot for a bookcase. Perfect, except for the switch of a fused switched spur that fed the old immersion heater in the attic. The immersion heater had been stripped out and replaced with a combi-boiler in the kitchen so this was now redundant. So I figured  that the switch could come off the wall and the hole plastered over. I switched the circuit labelled "immersion heater" off at the circuit box, removed the faceplate and checked the circuits were dead with my DMM. At this point my GF was saying "are you sure you should be doing that? Maybe we should get an electrician in?".
Hey, I'm an EE and I know what I'm doing...

The DMM showed 0V so I got my trusty sidecutters and BANG!! As it turned out, the DMM had a latching button for HOLD and that had been accidentally pressed, and that circuit was a spur from the sockets.

I don't know what was more damaged, my sidecutters or my reputation. Needless to say, she takes great delight in recounting the story.

[IanJ]

Last weekend:

A mate said his cooker hood was intermittent, the lights flashed/pulsed and the fan had trouble starting.
Sounded like bad caps on the control board so I went round. We powered the hood down at the fuse box, I checked no mains present at the hood and removed the control board. The caps looked ok, but decided to take the pcb away and change them anyways........

I returned an hour later and went to work re-fitting the pcb........BANG!

So my mate had turned the hood power back on at the fuse whilst I was away!........for the kettle or something.

Ian.

[TheAdmiralty]

...Welp, if you're going to make a PCB using an excessive amount of surface-mount tantalum caps, make sure you link the anode and cathode on the footprint to the proper schematic pins.

It's quite a sight watching 26 significantly large tantalums all vaporize at the same time when hit with -12V.  Makes sense now why they list a risk of "detonation due to catastrophic thermal runaway" when overvolted into a short, though I'm not sure reverse polarity really applies to that.   

I've developed a bad habit of double-checking everything after a run of prototypes have been sent in for fabrication.  I wouldn't recommend it at this point.

[Cyril.Anthony]

When i was a noob i thought the marking in tantalum capacitor signified negative like in the electrolytic capacitors. lol i was soo wrong that small 22uF capacitor blew like a fire cracker

[basinstreetdesign]

If you want to talk about expensive mistakes...
Some decades ago I worked for a small (5-7 employees) broadcast video manufacturer in Toronto and as I was the resident technical knob there, I was given the task of organizing the manufacture of 50 new copies of a standard product of ours, a time code reader with a lerge 2-sided board.  The pcb layout was done as two-colour tape on a polycarbonate film which was then photographed and colour-separated to produce the master production negatives for the PCB fab shop.  These films happen to have no textual info on them except silk screen legend.  I got the boards underway and then bought all of the parts and when they arrived got the girls to assemble them.  My boss decided he would try out one of the first to be ready.

The board shop assigned the top and bottom negatives of the copper layers at random, assuming it didn't matter and went ahead with it.  This wouldn't have mattered to the operation of the circuit except that there was an edge connector on it.  A big one.  All of the top-side pins and bottom side pins of that edge connector were swapped and proved to be unfixable making the entire run of boards scrap.  We lost a lot of money and 6 weeks in that screw up which could have been avoided in about 1 minute of correctly marking the artwork with a sharpie.

My job survived but not by much.

[raptor1956]

Many moons ago, while working as an Avionics Tech in the USAF, I was working on a panel light on the instrument panel and since it was 28VDC I didn't feel any need to power it off first.  So, I grab the thing and am working on it and I leaned in and my upper lip touched the yolk.  The 28VDC went into my hand, through my body, and exited through the contact patch my lip made with the yolk -- it felt like someone jammed a knitting needle through my lip -- f'n hurt like hell!

So, don't mess with 28VDC.


Brian

[eugenenine]

I did similar but it was the strip the wire with your teeth on a telephone ring generator that I thought was not powered on.

[ptricks]

I cut the end off a usb cable and assumed red was positive and black was negative.
Apparently china doesn't care about wire color,  I let the magic smoke out on a very expensive circuit due to reverse polarity on the wires.

[meeko]

Maybe not the stupidest, but probably the biggest bang I've made...

Taking electronics in high school, the lab had a big power distribution panel, that fed 120V/15A AC, variable AC and variable DC (the same voltage to every desk) to all the desks.  Then each desk had a grounded metal box with the various connectors.

We were building a mains lamp flasher, with a 555 and a relay.  The lamps were powered from pigtails plugged into the 120V outlets, with bare wires that we hooked onto with alligator clips.  I bumped my mains wiring, and the hot came too close to the side of the power box, with predictable results--a flash and a bang.  There were individual breakers for each desk, but I guess only 1 GFI on the input to the distribution panel, and that was what tripped, so I knocked out everybody's power.  Whoops... 

[dimkasta]

From an early age I exhibited a tendency to take apart and "fix" anything around my house that we did not necessarily need anymore.
All I needed was my screwdrivers and my tongue firmly attached to the right side of my upper lip for extra concentration.

The scariest thing I ever did (not realizing it then of course) was taking apart my grandfather's tube radio. Fortunately, it seems I was lucky enough to never touch any capacitors

And the second one was to connect an old washing machine motor directly to mains to see if it would turn. Fortunately for just a split second.

I always was a fraidy-cat with mains voltages, and thank God for that. I have a few melted test-screwdrivers as a reminder that it's always right to be paranoid about mains voltages.

It's the same thing with guns. It is the empty/safe ones that kill.

[eugenenine]

the washing machie motor reminds me.   We picked up a treadmill from the curb and it has a 90vdc motor.  I showed my son how to colder up a bridge rectifier so we could test the motor from mains.  He soldered it up and was ready to plug it in as I was yelling 'wait'.  The big flywheel was heavier than the motor so the motor started turning at full speed winding the wires around it as it pulled the plug back out of the wall and his hand.  he took off running as fast as the cats did.

[Tom45]

Hard to say what my stupidest mistake might have been, but a memorable mistake was when I set my house on fire.

Nearly 60 years ago when I was a kid experimenter, I built a Jacob's ladder using a neon transformer in my basement workshop. It worked quite well. Then, leaving it on, I went upstairs to get a snack. While eating I smelled smoke. Ran downstairs and found my workshop on fire. The arc had set some nearby paper on fire. I managed to get it put out before the fire department arrived.

Wikipedia has the following in their article on Jacob's ladders:

Traveling-arc devices are dangerous. The sparks can burn through thin paper and plastic and start fires, and contact with the exposed high-voltage conductors can be lethal.[citation needed]

Citation needed? 

I didn't stop to think about the possible fire danger although I was well aware of the high voltage danger. But if someone had told me at the time that there was a fire danger I surely wouldn't have said "I don't believe it. What is your source?".

[Codebird]

We picked up a treadmill from the curb and it has a 90vdc motor.

I've read those are good motors for using as dynamos in DIY wind turbines.

[eugenenine]

We picked up a treadmill from the curb and it has a 90vdc motor.

I've read those are good motors for using as dynamos in DIY wind turbines.

Thats what I've seen too.  Going to put one up beside the cabin someday.

[8086]

When I was about 5 years old, I put a lemon shaped soap into a lamp fitting.

Luckily, it was off.

 

[meeko]

When I was about 5 years old, I put a lemon shaped soap into a lamp fitting.

Luckily, it was off.

 

Doesn't really count, as it was in a role-playing game, but one time a (female) character I was playing seduced the "big bad's" right-hand man, had "relations" with him then, when he fell asleep, killed him by jamming a certain lower-body appendage into a lamp socket and turning it on.  Yeah, that character was kind of messed up...

[LaserSteve]

Four foot long, brand new glass-ceramic Krypton  Ion Laser Plasma tube with gas ballast attached by 6" stainless steel corrugated flex line to the plasma tube/...  Was installing it into its water cooled magnet.  My helper had a muscle spasm..  My boss heard me yelp when the flex line cracked.  Near tears, thinking my job was over due to 7500$ loss, heard, in deep Russian accent,  "You have served us well over many years, you get a mistake once in a while.   Personally drive to the factory in St. Louis and pick up  another one, see it running there. The purchasing  paperwork will be done before you arrive.  Install it yourself, like you usually do without the helper  and be back here in three days, I have research to do..."    I could not believe my ears...   I set a new record for Cleveland to St. Louis, installed a new one there, and set a new record for slowest  drive with a fragile object on the way back...

Steve

[eugenenine]

Doesn't really count, as it was in a role-playing game, but one time a (female) character I was playing seduced the "big bad's" right-hand man, had "relations" with him then, when he fell asleep, killed him by jamming a certain lower-body appendage into a lamp socket and turning it on.  Yeah, that character was kind of messed up...

Yea, sure, it was the characters idea.

[Deridex]

my most stupidest mistake is something i did quite a few times:
I did not check the voltage of a powersupply despite the fact that i knew it was unrealible.
Result was: smoking stuff on boards
At least my coworker roasted a few boards that way too...

[RoGeorge]

https://hackaday.io/project/7590-retardo-davinci

[TheWelly888]

Touching the metal tab of a switching FET on a live SMPSU, fortunately it was running from an isolated 115V source!

[SingedFingers]

I just spent three weeks procrastinating on a project because I couldn't find a 5 position rotary switch because the  12 way one I have has too many positions 

(for those who don't know, there is a little latching bar you can adjust the travel to any number between 2-12 positions)

I've only been using these switches 20 years and never even noticed it until 5 minutes ago.

[dimkasta]

Which reminds me...


Can's say if he's trolling or if he's just plain stupid...

[kolbep]

My Most Stupid (and Costly Mistake), Warning, EXTREMELY CRINGEWORTHY

Customer supplied a decent size Variable Speed Drive (Inverter) for one of their Oil Circulation Pumps (A large Oil Factory).
Ok, So install an outdoor enclosure, isolator, run the 3 Phase 400V Supply. Then check that the Inverter supply must connect on the bottom right of the Inverter, with the Load on the bottom Left. Ok? that seems opposite to convention. Double Check it according to the Manual, yep that is the way it is supposed to be.

Guess What I do? Yep, Even after double checking, I went and hooked the supply up to the left, and the load to the right.
Switch on the Isolator, and there are Sparks, Flames and Smoke. Completely destroyed the Output Stage of the Inverter, as well as the main control board. ZAR15000 Later for a new VSD, I have learned my lesson. I now check it 5 times, and also have my helper double check...