Lenovo’s retro ThinkPad 25 laptop leaks | 19mm Momentary Push Button

@ [Martin] DC can kill you hours later because it goes through your body like lightning, it takes the path of the lowest resistance (usually the most moist path) and cooks everything in it’s path including vital organs.

“If you can power the logic side with some +5V derived from mains, there is no point keeping the optocouplers, right?”

He did specifically mount/build that setup around the possibility of failure. He talks about it in the first few minutes of the video. Kinda a hyped up headline.

I’ve been looking for a capacitor for microwaves. I have this idea that I could use it for warming my coffee on the beach.

Still can’t bring myself to install SSRs on “high current” applications, either. High quality mechanical relays.

Clearing the work space and moving any furniture before I arrive means I can get in and out faster, so I can charge you for less of my time.

You are right, FR-4 has a glass transition temperature of around 120°C, so if you heat up your traces above that, and take into account the mechanical stress from expanding copper traces, delamination is something waiting to happen sooner or later (especially if you design corners in your traces). Add to that the fact that you usually don’t measure the temperature directly on the traces to regulate input power, you could go way beyond 120°C in your copper traces. I don’t think a lot of DIY guys actually know that there would be high-TG materials on the market better suited for PCB based heater applications…

You don’t need a big contactor to switch 1A at 120v, you can get little “ice cube” relays that switch up to 10A at 120V and they have a plug-in base so easy to change out when they inevitably fail. Most of them, in new perfect condition, make barely any sound. Nothing compared to the noise of fans and stepper motors. The only issue I can see is running AC mains voltage through wiring that is going in parallel with low voltage. Would need to use thick jacketed, shielded cable to prevent too much EMI. Maybe it’d be better suited using a separate transformer just for the heated bed, rectified/regulated but still a higher voltage for better efficiency. Speaking just from my experience as an electrician and hobbyist level electronics/3d printing experience.

The third incident was also while I was working for the welding repair company. I had a previously perfectly working high-pot tester and needed to test the insulation on a transformer. The tester itself failed and shorted to the case – and I took 11kv AC to the fingers just by turning the power on. That stung a bit, but I got a new high-pot out of the deal, so a net positive.

– Use isolated differential probes to measure high voltage. – Use current clamps or current transformers to measure current. – Put bleeding resistors in any big capacitor in your circuit. – Don’t change the position of the probes in the power circuit without power everything down. – Don’t work with high voltages alone. – If there’s more people involved in your experiment, block any circuit breaker, button or at least put some signs to prevent people from turning them on while you are messing with the circuit. Paranoids may even ground things while they are playing with the installation to direct the current to the ground in case someone makes a mistake.

The only thing I would add would be a (redundant) circuit breaker (Airpax, Heinemann, et al) on each input that was two-pole with a common trip bar. That, and I would build it in a metal enclosure.

my first “real” job was in a video game arcade back in the 80’s my boss was a really cheap prick that used to buy asian cocktail machines that were “native” 110V, with a 240V to 110V step down transformer wedged in where it would fit, my second day I was fishing out a 20 cent coin that had missed the coin box, I got “zapped” hard enough to blow my finger nail in half and stop my heart.