Best approach for heating small lengths of nichrome at 220 volt

Question

I got a length of 5 meters of Nichrome wire from a toaster that works on 220 volts. Its rating is 800 watts and its specific resistance is 12 ohm/meter.

For my small oven-project, I only need a half meter of the wire. Plugging this wire right into the mains does not work en is even dangerous, right?

So I have 4.5 meters of surplus wire. The most easy, but also must inelegant solution will be to just leave these 4.5 meters connected to my small oven. And then connect the whole thing to a wall outlet.

What is a more elegant and feasible solution to lower the voltage over the 0.5 meter of Nichrome wire? I was thinking of placing resistors in series/parallel, or connecting a transformer / dimmer?

Answer 1

If you only need 80W then you can use a 22V 80W supply. If the supply is galvanically isolated this could also be safer from an electrical shock pov.

Obvious candidates would be to use a 19V laptop power supply or a 24V open frame power supply and adjust the length or the voltage (where adjustments are available) slightly. Output current will be about 4A.

If this is a real problem rather than a homework question or gedankenexperiment, re-using nichrome heater wire may not be all that easy- it tends to get brittle after being used for some time.

Answer 2

If 5 meters is 800 W then 0.5 m on the same voltage will be 10 times as much

So expect 8 kW. With sufficient cooling the wire will probably survive, but supplying 8 kW will need some effort... I mean that'd be crazy, and you want it for small oven. it's not going to work

What is a more elegant and feasible solution to lower the voltage over the .5 meter of Nichrome wire? I was thinking of placing resistors in series/parallel,

Resistors: that is basically the same as your your plan A - leave the remainder connected and use it as a room heater.

or connecting a transformer

This is probably the best solution

/ dimmer?

A dimmer could work, but the setting would need to be very low, like 10% of full power, it would probably annoy the power company due to its poor power factor, and annoy neighbors with radio interference this will require a special industrial grade dimmer. This approach seems fraught...

A dimmer on the whole 5 m element could work (if you can fit it all into the oven), but still you'd probably need a dimmer rated for 800 W.

Option D is to find some finer (higher resistance) nichrome wire, it will several meters long for 80 W, so you'll need to zig-zag it in the oven, perhaps wrap it round a mica sheet.