Homebrew heaters using resistors?


First time poster! :)

I've been reading up on some projects on this site centered around small homebrew heaters. One I came across I want to adapt is using two resistors and usb port power to make a small coffee mug heater.

I'm kind of a novice at electronics, but I'd like to know how to design such a heater with safety and functionality in mind. I also want to control this heater via arduino if I can get a prototype together. Some questions I have:

Where to get and what kind of resistors for heaters?
How do I figure out what resistors to use based on power. e.g. 12v or USB power?
What's a good thing to "encase" the resistors with that will withstand heat? I have thought about using radiator repair epoxy.

Thanks for any help!

harry886 years ago
use a peitler attached to a small fan
lemonie7 years ago
Pull apart an old toaster / hair-dryer: they contain exactly the sort of resistive heating elements that are good for heating. But as guy has observed, you don't get a lot of heat from a USB port.
Car-exhaust-repair compound will be better than radiator-compound.

guyfrom7up7 years ago
Well you arn't going to get much heating out of a USB port, the maximum power from a hi-power USB port is 5 volts at 500mA (0.5 amps), which translates into 2.5 watts.  That's not too much heat.

Power (watts) = Current (Amps) times Voltage (volts)

Voltage (volts) = Current (amps) times resistance (Ohms)

so try and maximize power thats still within your power supply's limit.

Also, the best thing for heaters is actually called "Nichrome" wire.  It's pretty much a resistive wire that can withstand fairyl high temperatures.  It's primary use it for heaters and igniters.

As for encasing, I'm not too sure whats a good material