Yes, the Samsung Galaxy S9 has a headphone jack | 19mm Momentary Push Button

For transient rise times of 0.1 to 0.2 μs, twice the unit value of surge capability is required on stator windings. When rise times reach 1.2 μs or greater, 4.5 times the unit value is stipulated. In the case of external transients such as lightning, this would equate to a surge voltage capability of 918 VPEAK for a 230-V motor (full load current = 12 A) on a 250-V high-line condition. (Lightning surges can exceed these values, so stator windings would also need a suppression element for protection.)

Agreed…. I used to have a small plastic box in our workshop. It had two copper contacts on opposite surfaces, and a 9V battery, relay and tilt switch inside, and a Caution High Voltage sticker on it,

I flashed Tasmota firmware onto the Sonoff, and configured GPIO2 as a counter, and I now have the whole setup reporting to Node Red, which switches the pumps on and off on schedule, or as desired. I’m quite chuffed with the result, although now I need to learn a lot more about how Node Red works!

The problem is that the triac may dissipate more than 15W when using it at 10A, which requires a good heatsink and ventilation. That’s a lot of overkill if you just want to control a 6W LED lamp.

That said, 12A @ 240V is only a little less than the most our Volt will use even on a proper charger, so it’s still a good thing.

But at the end of the training it says “you can ignore all of this if you are troubleshooting”. If you are afraid of live circuits, stay at your desk where it is safe…

The crimp terminals I am using are rated for 24A, and I am using a ratcheting crimping tool. I have checked, and therefore I do not believe you.

I have used a setup like this using two back-to-back “door-bell” transformers (220V to 9V) to play with neon tubes when I was a kid. The current was so low that even a lightbulb wouldn’t turn on. However, it was enough to teach me about electric shock from mains voltage when I have carelessly put my finger across the output terminals …

I’ve spent four to eight years in apprentice school learning how to plan, install, inspect, and repair electrical products. Don’t insult my intelligence by implying otherwise.

The control circuit for the 12V/24V can be as simple as a MOSFET and don’t even need to be isolated if you know what you are doing. Because you are using a regulated supply, the same heated bed can be used at different countries with different voltages. The safety regulatory stuff get you covered as 12/24V are considered to be low voltage.

Your friend died of what and why? Testing mains voltage across the back of his hand? Please. Mains voltage is not scary if you know what you are about. I dealt with volts up to 132KV and mega amps and megawatts in my career I worked in the UK electrical power industry.

Step 2:  To determine which MOV disc size to use, first identify the MOV series that minimally meet the 1000-A surge requirement. Inspecting the table above suggests a 20-mm MOV with a 31-V dc maximum continuous voltage rating (part number V20E25P) as a possible solution to meet the requirements.