this post was submitted on 15 Mar 2025
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[–] brucethemoose@lemmy.world 208 points 1 day ago* (last edited 1 day ago) (4 children)

Shoudn't it be 25%?

Current is not controlled here, resistance (aka the soldering iron) and voltage are.

Power = Voltage ^ 2 / Resistance. Double the voltage, that quadruples the power. So you only want to plug in 25% of the time to get the equivalent power of 120V.

But it might not melt at double power? Maybe the extra heat helps, I can't find a resistance/temperature curve for a soldering iron...

Source: EE dropout.

[–] homesweethomeMrL@lemmy.world 115 points 1 day ago

nnnNNEEEEEEERRRRRRRRRd!

[–] uneatable@lemmy.world 14 points 23 hours ago (3 children)

Ok. I was acountless on lemmy for a long time, your comment made me finally register. Thanks!

So, yeah, with double the voltage you get 4x the power. But you you put 4 times the power at 50% of the time, you get only 2x the power. And the other half of the time, you get 0 power. On the average you get the same power output.

[–] ch00f@lemmy.world 23 points 22 hours ago (1 children)

You double counted there.

You said 4x power 50% of the time and then said “the other half of the time.”

So you’re calculating 50% of 50% which is 25% duty cycle.

[–] uneatable@lemmy.world 16 points 22 hours ago (2 children)

Oh no, I didn't. Should I draw a graph? Pop out some equations?

Let's say P is the nominal power. When I said "The other half" I meant when the solder iron is not plugged. So:

50% of the time at 4xP 50% of the time at 0...

Oh shizzzz, you're right!

[–] Riprif@lemmy.world 2 points 16 hours ago

I imagine this is more or less what it felt like to be in the room at the time. A whole group of people discussing electrical theory and optimal soldering techniques and meanwhile the one guy standing there holding the actual device notices the power cord is a little loose and pushed it in another 1/8" without mentioning it because everyone is so involved in their nerdy conversation.

[–] Juvyn00b@lemmy.world 2 points 21 hours ago

Oh man I was going through it in my head too...

[–] brucethemoose@lemmy.world 7 points 20 hours ago (1 children)
[–] uneatable@lemmy.world 5 points 19 hours ago
[–] brucethemoose@lemmy.world 1 points 21 hours ago* (last edited 20 hours ago)

I had to think about it too, lol. This is an equation for DC/instantaneous power, and if you want to get into AC math, this is more like a square wave. Averaging the power out over time doesn’t necessarily work with the equation, as you figured out, as it doesn’t when you try to measure AC (sinusoidal) power by average voltage or whatever.

[–] ch00f@lemmy.world 47 points 1 day ago (1 children)
[–] rickyrigatoni@lemm.ee 18 points 1 day ago (2 children)

If only the oop was here to see this 😔

[–] ch00f@lemmy.world 9 points 1 day ago

In my defense, I've been helping a friend with an EVSE install where the load (electric vehicle) is smart. In that context, it's just voltage X current capacity of the line = power. The rest of the story is true as far as I know.

[–] 0ops@lemm.ee 4 points 20 hours ago

What are you lookin at

[–] Cenotaph@mander.xyz 16 points 1 day ago (1 children)

I sure hope someone will be fired for this obvious blunder

[–] Rooty@lemmy.world 2 points 15 hours ago (1 children)

If my company fired people for trade show cock-ups we would change the entire staff every couple months. There is a lot of stuff being moved in a short time period, shit is stressfull and you're working at a diminished capacity at least a week aferwards. As long as the stand is not on fire during the show, all is good.

[–] Cenotaph@mander.xyz 2 points 14 hours ago

Oh, absolutely. I was just making a bad simpsons reference