982
PWM power supply (szmer.info)
submitted 4 days ago by Ludrol@szmer.info to c/microblogmemes@lemmy.world
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Source: https://lemmy.world/comment/15569796

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[-] brucethemoose@lemmy.world 205 points 4 days ago* (last edited 4 days ago)

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 117 points 4 days ago

nnnNNEEEEEEERRRRRRRRRd!

[-] ch00f@lemmy.world 48 points 4 days ago

Right you are. Oops.

[-] uneatable@lemmy.world 17 points 4 days ago

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 22 points 4 days ago

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 15 points 4 days ago

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!

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[-] brucethemoose@lemmy.world 7 points 3 days ago

Also, welcome to Lemmy!

[-] uneatable@lemmy.world 5 points 3 days ago

thanks!

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[-] Cenotaph@mander.xyz 16 points 4 days ago

I sure hope someone will be fired for this obvious blunder

[-] oldfart@lemm.ee 26 points 3 days ago

Finally, an usecase for USB irons!

[-] Bronzie@sh.itjust.works 6 points 3 days ago* (last edited 3 days ago)

I just got one, and it’s so practical with a PD battery bank. Can now solder inside or outside on my car/bike with zero hazzle

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[-] EmoDuck@sh.itjust.works 76 points 4 days ago

There are gas powered soldering irons that are essentially lighters with metal around the flame. Real life savers

[-] zaphod@sopuli.xyz 67 points 4 days ago

There are also battery powered soldering irons.

[-] BastingChemina@slrpnk.net 39 points 4 days ago* (last edited 4 days ago)

I like the pinecil, usb-c powered soldering iron with temperature control. If you are not doing anything intensive any fast smartphone charger will power it.

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[-] melpomenesclevage@lemmy.dbzer0.com 13 points 4 days ago

yes but that sounds boring and doesn't require having a functionally super-hot piece right near a reserve of acetylene.

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[-] jpreston2005@lemmy.world 58 points 4 days ago

It's only stupid if it doesn't work

[-] Xatolos@reddthat.com 53 points 4 days ago

Should have just left it in, and been able to get the soldering done twice as fast.

[-] betterdeadthanreddit@lemmy.world 18 points 3 days ago

New manufacturing hack unlocked: Install 240v outlets at workstations and fire half of the workforce. Golden parachute and douchey, hand-wavey TED Talk, please!

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[-] melpomenesclevage@lemmy.dbzer0.com 42 points 4 days ago* (last edited 3 days ago)

there's the STEM bell curve. XKCD shows the axes as 'how well your computer works' vs 'how well you know computers'. that is accurate.

but if you've ever known serious engineers who didn't just live boring white collar work-home-work-and-some-marvel-shit lives, you'll have seen things that make this look mild.

edit: and it gets really crazy when you're talking about a civil engineer. closest thing you'll ever find to an eldritch location.

[-] anton 50 points 4 days ago


xkcd.com/1785

[-] melpomenesclevage@lemmy.dbzer0.com 5 points 3 days ago

I think there's another one, where the right side references operating systems, and another without the graph that's along similar lines. long runners sometimes return to the same wells, I guess.

[-] affenlehrer@feddit.org 20 points 3 days ago

I've had a similar experience as a child. I live in Germany and found this voltage switch on a hair dryer. My thoughts were like: Switching it to less couldn't possibly hurt, could it? Well it could. It was super efficient though but only for a few seconds before it self destructed.

[-] tfowinder@lemmy.ml 23 points 4 days ago

Don't they have switches?

[-] farcaster@lemmy.world 25 points 4 days ago

Sounds like a cheap portable soldering iron, which just heats up to some roughly usable temperature whenever it's plugged in.

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[-] RisingSwell@lemmy.dbzer0.com 12 points 3 days ago

Why plug and unplug? Doesn't the wall outlet have a switch?

[-] Azzu@lemm.ee 40 points 3 days ago

I have actually never met a wall outlet with a switch.

[-] RisingSwell@lemmy.dbzer0.com 14 points 3 days ago

Really? Where are you for that? I don't have a wall outlet without a switch, and I've never seen one because why would it just be live all the time?

I'm in Australia for reference.

[-] Tenniswaffles 34 points 3 days ago

We're the exception, most places don't have switches on their outlets.

[-] nik9000@programming.dev 14 points 3 days ago

Looks like it's mostly a UK, Australia, and New Zealand thing.

[-] crmsnbleyd@sopuli.xyz 4 points 3 days ago

India as well!

[-] southernbrewer@lemmy.world 3 points 3 days ago

I'm in NZ and I've always hated it. Someone always goes and switches them off, and they're totally unnecessary when every device already has its own switch

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[-] Azzu@lemm.ee 13 points 3 days ago* (last edited 3 days ago)

Germany. It's just live all the time, because why wouldn't it? If you plug something in, you want it to work. If you don't want it to work, you either plug it out (which works just as well as a switch, with the same convenience), OR you use the switch at the appliance because why would you try to reach the hypothetical switch at the wall outlet if the wall outlet is behind a drawer, under a table, or whatever inconvenient place? I use my remote control to turn the TV on or off, I don't physically walk to the wall power outlet.

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[-] Johanno@feddit.org 8 points 3 days ago

Afaik it is a safety thing that is handled differently in different countries.

Uk and their colonised countries have this. The reason is that the fuses are in each plug. But no (or almost no) fuses in the power grid of the house. In Europe most countries have a single GFCI and several fuses for power grid sectors in a single place in the house where the power comes in.

I assume the switches on the power outlets are for turning off a switch because there is no GFCI in the house.

[-] jeeva@lemmy.world 5 points 3 days ago

I think in the UK at least this view might be a little outdated - every house I've ever lived in has had GFCI sectors across the house, or had to be updated to have it when work was done.

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[-] Fermion@feddit.nl 20 points 4 days ago

They need a 1/4 duty cycle.

[-] RangerJosey@lemmy.ml 9 points 3 days ago

Hey. If it works, it works.

Any port in a storm right?

[-] Kaput@lemmy.world 16 points 4 days ago

Person Wait Modulation.

[-] observantTrapezium@lemmy.ca 13 points 4 days ago

I had the opposite problem, I brought a soldering iron from Europe to Canada, and despite using a step up transformer, it just couldn't get hot enough to melt the solder!

[-] lauha@lemmy.one 24 points 4 days ago

You should have used 200% duty cycle

[-] TomMasz@lemmy.world 11 points 4 days ago

Reminds me of the time when I helped install some 120 VAC ceiling fans and the electrician* wired them to the 220 VAC line. They spun like a helicopter trying to take off.

*Worked for the local electric utility, we trusted him, foolishly.

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this post was submitted on 15 Mar 2025
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