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Homemade Electric furnace current question Answered

good day viewers!

I recently found out about the wonders of electric furnaces, cheap to run and no smoke.
I went looking around for some designs, there are some nice i'bles about it and I got very exited since my neighbours already start nagging when I strike a match, an electric furnace would be the perfect solution.

I decided to go with kanthal wire, its relatively cheap at a few bucks per meter, and it can handle temperatures up to  1300C.
I plan to melt alluminium and maybe some brass so I should be fine with that.

now to the questions part, I have an ATX PSU with a 12V 16A output (DC), I was wondering how many (centi)meters or inches for the americans under us, it could power (if I can power it it would eventually go up to full temp right?)
I am a complete nitwit at these Ohms formulas and electric furnaces, at the moment I am abstaining from sleep to build this furnace and I am sure that others are as well.
I hope some nice fellow diyers can help me with it.
This could be a dumb questions, maybe I need a wall outlet (230V in my place) or maybe I need some rocket science.
I don't know, do you?

kind regards and a thank in advance from 2 young exploramenters that want to melt some metal without ruining our lungs.

excuse us for spelling mistakes, this written by non-native speakers and with shaking hands,...

Discussions

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gmoon

3 years ago

Ohms Law is your friend -- it's not going to tell you the heat output (other calculations can convert watts to BTUs or watts to caloric output), but it will let you calculate the resistance needed for a specific wattage target (at your voltage). Your heating element wire will have a resistance per foot rating.

I've taken apart simple resistive heaters with power outputs of 1000W and 4000W. Ohms Law says R = V^2 / P, or Ohms = Volts squared / Watts.

The 4000W 120V heater: 120 * 120 / 4000 = 14400 / 4000 = 3.6 ohms. Which isn't much resistance, and a lot of heat. Drawing 33.3 Amps, so an ample circuit, with large supply wiring is required. Good high-capacity switches are needed too.

You can use multiple lower-wattage elements (loops) to control the heat output. You can probably guess the wattage requirement with a little research on the types of heaters you're emulating. These calculations need to be done at your voltage, of course.

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JStuyfzandgmoon

Reply 3 years ago

I am planning on using 25 meters of wire, which give 7 amps on my 220V outlet, is 7 amps enough heat?

How do you calculate how fast the wire gets hot with x amount of amps?

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gmoonJStuyfzand

Reply 3 years ago

Wire doesn't have much mass, so it probably reaches full temp in a short time. However, the more wire, the greater the resistance and the longer the time. The lower the wattage (fewer amps & volts), the longer the time.

Your heater is 1540W (W = amps * volts) which isn't all that much wattage -- but the final temperature depends on the area heated, and the surrounding insulation. 1500W is probably plenty to heat a small area, but spread over 25M of wire, that doesn't seem very concentrated. 25 meter of wire would require a LOT of space.

Also, heavier-gauge wire = less resistance per length = more current draw = more power = more heat...plus thicker wire is probably more robust.

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JStuyfzandgmoon

Reply 3 years ago

the area heated is 0,15 cubic feet, will 1540 be enough?

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gmoonJStuyfzand

Reply 3 years ago

Don't know! But that's a fairly small area, for sure.

If it's well insulated, maybe?

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JStuyfzandgmoon

Reply 3 years ago

Can`t deal with maybe! :D

I have a transformer, I could run some sweet amps through it, would this help?
I mean, a 500 amp - 1v arc furnace makes more heat than my one I guess

:D

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gmoonJStuyfzand

Reply 3 years ago

Power is power: 500A @ 1V = 500W, which is considerably less than 1540W. Probably an efficiency / design thing.

The more power you input, the greater the heat, so it comes down to design considerations. Kinda like how a microwave oven heats only the food, so it's much more efficient -- the smaller the area you're heating, the greater the efficiency.

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Downunder35m

3 years ago

You don't want to power the wire directly without control.
I use a PID controlled temp module to get the temperature I need.
And I use 1000W heating elements for 240V - they come in a spiral already and only need to be stretched out a bit.
PID controller are around 30 bucks on Ebay and well worth it.

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caitlinsdad

3 years ago

Search for electric furnace or kiln, lots of ibles on that. A typical space heater can run at 1500 watts so I'm not sure a typical 500w atx power supply will cut it or even necessary since the heating element goes straight to the wall. Good luck.