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Comment by kens | Hacker News Reader

> you could see multiple joules of energy into your device

Is that supposed to be a lot? Your phone receives multiple joules every second when charging, even with a slow charger.

One watt is one joule per second. Most things designed to consume power, especially related to wall devices and consumer electronics you'd charge, are capable of ingesting multiple watts. Most things that aren't, aren't. The difference that I'm not sure I'm seeing from the other comments is that a phone takes that energy and stores it as a chemical reaction, with some losses as heat. For everything else, it's all heat. Also, it's uncontrolled. The phone charger circuit can be upwards of 95% efficient, so very little power is getting turned into heat. The ADC input to your scope, on the other hand, would turn 100% of that into heat, which is why it'd blow up.

Practical example is the 50 ohm term. Most scopes I've seen max that at 5 Vrms. P = V^2/R, so 0.5W being dissipated. Now assume you hooked your scope to mains and accidentally turned on 50 ohm term. A low mains voltage is 100Vrms. That's 200W. 400x the maximum. Could a device take 200W? Sure. Could that device? No

It's a question of energy density. Multiple joules into your big phone battery is nothing, multiple joules into a small SMD component means it evaporates immediately in a bright flash!

Yeah, and batteries are deeply weird in that they're a component you put power into and they mostly don't get warm.

"slow" is still measured in milliseconds. That said, the energy is probably in the low hundred Joules. which is a lot when theres no time to dissipate it.

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