Ni-chrome wire not heating

Hi all...
i am trying to build a small heater using a 1.5mm dia nichrome wire. initially i tried using a small piece of wire around 20mm length and connected to a 12V,2A DC power supply. but instead of wire getting heated up, the DC power supply gets shorted. why this thing happens. do i need to add any circuit to control nichrome wire.

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the same i got 0.2mm dia nichrome wire... it works great with 12v power supply. then why do this 1.5mm dia wire creates an issue.

Because thicker wire of the same type has a lower resistance. You are simply overlpading the power supply.

The heat produced is proportional to the current squared multiplied by the resistance of the wire, by making the resitance lower the power is reduced.

Brian.

gauravkothari23 said:

i am trying to build a small heater using a 1.5mm dia nichrome wire. initially i tried using a small piece of wire around 20mm length and connected to a 12V,2A DC power supply. but instead of wire getting heated up, the DC power supply gets shorted. why this thing happens. do i need to add any circuit to control nichrome wire.
the same i got 0.2mm dia nichrome wire... it works great with 12v power supply. then why do this 1.5mm dia wire creates an issue.

Click to expand...

You need to use some calculator to compute the power. The fat wire does not work because your power supply does not have zero internal resistance and cannot supply infinite current (you mentioned 2A).

If the thin and thick wires are of the same length, the fat wire has 1/56 times the resistance of the thin wire. If the fat wire has a resistance of 1 Ohm, the thin wire will have a resistance of 56 Ohm. (it is proportional inversely to the cross sectional area).

At a constant voltage, the power delivered to the load will be V^2/R; lower resistance wire is supposed to get hotter. But it does not.

The power supply clips the current output at 2A; the power output at const current will be (I^2)*R; higher resistance wire will get hotter.

Real life is different. Your power supply can deliver 12V*2A=24W max. Because it will have some internal resistance, it cannot deliver more than 12W to the load (funny, right?)- the remaining 12W will be dissipated within the power supply.

Select your nichrome wire accordingly.

Discovered ohms law?

The said piece of wire has about 12 mOhm resistance at ambient temperature (in case of Ni80Cr20). Power with 2A is only 48 mW, you can safely touch it.