Electronic – Heating up a nichrome wire, MOSFET got too hot

mosfettemperature

I'm trying to get a 37 AWG, 0.6mm diameter nichrome wire to reach 300*C so it can heat up inside of an enclosure and according to its datasheet that requires 5A, I cut out enough nichrome wire to offer 2.4ohm. The source provides 12V and 5A max, the MOSFET used is STFH18N60M2(datasheet) and it acts as a switch and I'm sending a PWM signal(%100 duty cycle at the moment) to its gate from Arduino.

Now the nichrome wire does heat up, I don't know if it reaches 300*C but what went wrong is that the MOSFET apparently got too hot and melted the plastic of the breadboard where it was connected, I didn't think I would need a heatsink and I'm wondering if something is wrong with my circuit:

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Best Answer

Your heater at 2.4 ohms with 12 V will draw a current of I = V/R = 12/2.4 = 5 A.

While that is within the capability of the MOSFET's 13 A rating, you are failing to account for the power dissipated in the MOSFET itself.

At 5 A and 0.280 ohms RdsON you will get P = I^2*R = 5^2 * 0.280 = 25 * 0.280 = 7 watts. The datasheet shows a Rthj-amb of 62.5 C/W.

So 7 watts will give you 7 * 62.5 = 437 C! That's WAY too hot. The max operating temperature is 150 C.

You need a heatsink capable of keeping the device below 150 C or you need a different MOSFET that will not dissipate so much heat.