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I want to build a toaster just for fun. I want to buy a nickel chromium wire to heat the toaster's plate. How to avoid burning my power adapter cuz the resistance is too low. I currently have a variable power adapter that goes from 9 volts to 24 volts. At 9/12/13.5\15 volts it outputs 1.5Amps. At 18/20 volts 1.2 Amps and at 24 volts 1Amp

Thank you

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    \$\begingroup\$ Look up AWG and resistance/length for the wire and calculate it. \$\endgroup\$ – DKNguyen Sep 22 '19 at 18:23
  • \$\begingroup\$ How thick the wire should be and what the power supply requirements are depend on a thorough mechanical and thermal design. You have to start with a good set of specs, then from there do the mechanical and thermal design which will lead to the electrical and other requirements for the Nichrome wire. We can't possibly help you with all that on a site like this, so voting to close this as too broad. \$\endgroup\$ – John D Sep 22 '19 at 18:25
  • \$\begingroup\$ @JohnD i edited the question \$\endgroup\$ – Randomouss Stuffed Sep 22 '19 at 18:29
  • \$\begingroup\$ The maximum power you can get from your power supply is only 24W. You won't make much toast with that. \$\endgroup\$ – Elliot Alderson Sep 22 '19 at 18:30
  • \$\begingroup\$ That's better, but I was talking about specs for your toaster. How hot do you want the toast cavity to get? How much power do you have to dump into the cavity to get that temperature rise? You mentioned heating a plate, what's the thermal conductivity between the wire and the plate? What are your specs for thermal rise time? And as @ElliotAlderson said you're not going to get there with the 24W supply that you have. \$\endgroup\$ – John D Sep 22 '19 at 18:35
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A typical two-slice toaster uses around 1kW. That toasts about 4 x 5" x 4 = 100 square inches of surface.

You have no more than 24W. If we can do as well at lower powers, you would be able to toast about 2.4 square inches of surface or about two 1.1" square (27mm square) pieces. Not even the size of a piece of melba toast (and that comes pre-toasted). Maybe you can toast one side at a time, but still rather small.

Anyway, to calculate the resistance you decide whether to connect the (presumably) two sides in series or in parallel, and calculate the resistance from Ohm's law.

For example, to use the 24V you might connect them in series. You need 24 ohms to get 1A, so each one should be 12 ohms. Find a size of nichrome wire that will allow a decent watt-density (you want enough surface area that the wire will not burn up and will cover your desired surface area reasonably evenly). Here is a link that will help with estimating the desired wire gauge etc.

But it's not really much fun to make something that doesn't work, so I think you should re-think the power source unless you're making toast for your gerbils' breakfast.

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  • \$\begingroup\$ I want to toast one side at a time. What do you mean " to use the 24V you might connect them in series".You are talking about the 2 toasting surfaces? \$\endgroup\$ – Randomouss Stuffed Sep 22 '19 at 19:57
  • \$\begingroup\$ One side of normal-size bread, one piece at a time, you still should have about 10x as much power as your adapter can provide. Some olde style manual toasters did one side of two pieces at a time and made better toast, in my opinion (less dry). Maybe 600W for that. \$\endgroup\$ – Spehro Pefhany Sep 22 '19 at 20:05
  • \$\begingroup\$ but i still don't understand how i managed to light up a thin wire and smoke the entire room \$\endgroup\$ – Randomouss Stuffed Sep 22 '19 at 20:17
  • \$\begingroup\$ take this video for example, how he did that? youtube.com/watch?v=zFBGQH21yCE \$\endgroup\$ – Randomouss Stuffed Sep 22 '19 at 20:29
  • \$\begingroup\$ If you want to toast two surfaces at once you effectively need two heaters, so they can be connected in series or in parallel. Series requires heaters of 1/4 the resistance each compared to parallel connection. \$\endgroup\$ – Spehro Pefhany Sep 22 '19 at 21:47

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