Laptop power bricks is probably where I see it most. Or if you plug in something with a motor already switched on. Listen for a soft popping noise if you plug in a big power brick.
Many, many big power-smoothing capacitors inside those jumping from 0 to 120V in a microsecond, that’s why. The better-smoothed the power supply, the more capacitors and the bigger the sparks tend to be, although some really high quality ones put most of them behind inrush-current limiters to reduce the sparking, but that can also marginally reduce efficiency. High power electronics are always a bit of a tradeoff. The problem is that capacitors charge and discharge almost instantly in most cases, and when empty they act like a short circuit until they’re filled, so they can create some pretty big sparks, even though the actual energy going in is minuscule by any reasonable measurement. It’s almost like a static shock, huge spark, tiny energy.
Some motors will also spark badly when disconnected, but the reason is slightly different. They have a huge electromagnetic field which suddenly fills or collapses and that inductance in the coils can draw a lot of amps on startup and generate some pretty high voltages, more than enough to spark across the gap. Like the capacitors, they are very nearly a short circuit until they start moving.
Laptop power bricks is probably where I see it most. Or if you plug in something with a motor already switched on. Listen for a soft popping noise if you plug in a big power brick.
You’re right, now that I think about it. Laptop power does it more than anything else.
Many, many big power-smoothing capacitors inside those jumping from 0 to 120V in a microsecond, that’s why. The better-smoothed the power supply, the more capacitors and the bigger the sparks tend to be, although some really high quality ones put most of them behind inrush-current limiters to reduce the sparking, but that can also marginally reduce efficiency. High power electronics are always a bit of a tradeoff. The problem is that capacitors charge and discharge almost instantly in most cases, and when empty they act like a short circuit until they’re filled, so they can create some pretty big sparks, even though the actual energy going in is minuscule by any reasonable measurement. It’s almost like a static shock, huge spark, tiny energy.
Some motors will also spark badly when disconnected, but the reason is slightly different. They have a huge electromagnetic field which suddenly fills or collapses and that inductance in the coils can draw a lot of amps on startup and generate some pretty high voltages, more than enough to spark across the gap. Like the capacitors, they are very nearly a short circuit until they start moving.
Ah, this is fantastic. I learned some stuff, thank you.