/jp/ - Otaku Culture

Hmm, something about the warming guide is off to me.

https://controlc.com/9d4c2066..

Particularly lines like:
>You can also use powerbanks or portable chargers. Make sure to look at the output. Most powerbanks output at 5V, but amperage varies. I wouldn't dare go past 1.5A, though.
>Yes, you can use wall chargers and powerbanks for the warmer, the amperage is up to you
>The warmer, when plugged via usb, has a power output of 2.5W. That's 2.5J/s. It is safe to assume that you can use your warmer with a wall charger offering a higher current.
And the most damning line,
>The warmer is rated at 5V 0.5A, USB specifications. I do not know the effects of larger voltages on nichrome, but I do know that an increase in current should increase output. I use the warmer at 5V 1A, but I do not dare go past 1.5A for heating concerns. It is up to you if you want to use a 5V 3A tablet charger for faster heating times. Like with all things, I expect a decreased lifespan with an increase in power output.



In particular, it talks about plugging the usb warmer into varying usb ports as a way to regulate the current going to it, as if a 500 ma port is going to happy act as a constant current source for a device trying to source 3A.

But that's not how usb works, on a computer you'll either perm. blow a fuse if your computer is from the fucking 90s, or for anything remotely modern, trip a polyfuse.

More modern stuff will often pop up a "this port is drawing too much power warning" and disable the port until you re-enable it.
Either way, none of these methods will be happy to act as a constant current source, they'll mostly just shut down if over drawn. It's also not great for the port to keep doing this.

Some switching power supplies might actually act like a constant current supply once you go past their max, and others will just shut down.

And here's the kicker: Most computers built in the past decade will happily source 1-2A without complaining.
I just tested my desktop, and laptop, I got 1A with no complaints from both sources.
I even tried a chain of usb splitters, which actually dropped to .8A, but that's still significantly over .5A, and enough current to fully source the NLS heater I have, which I'm about to get to.

The ancient NLS heater I have has a 7 ohm coil resistance.

5/7 = .71, which this heater is never going to pull more than .7A.
Note that nichrome gains resistance as it heats up, but we can probably ignore that effect here as the current drop will be marginal.

So anyway, the TLDR; is despite what that guide says:
- Plugging into a computer usb port doesn't magically turn it into a constant current source.
- The NLS heater will try to source .7A, and most likely succeed from any computer made within the last 10-20 years. With the big caveat that my heater is like at least 5 years old now.
- There's no point in using a charger rated more than 1A with the nls heater, but it certainly won't hurt.
- If you want more current and more heat, you need to find a power source has a higher voltage, and can source enough current for your heater to sink. You will not find anything easily available with a USB form factor, so soldering something custom, or getting some weird adapter chain is a must here. USB can now output more than 5V thanks to USB-PD, but it will not do that without a USB-PD device negotiating said voltage on the other end, which these warmers certainly aren't doing. A sufficent voltage constant current supply would work well for this, but USB power bricks are not this.