# How to heat a shape memory alloy wire

I have read many articles online for heating the shape memory alloy wire using joule heating, so called direct current heating. However, if I connect the wire direct to the power supply, my power supply will switch to short circuit protection. Is there any suggestions for this ?

There are the specifications about the wire:

• Length: 305mm
• Diameter: 0.30mm
• Current Required for Austenite Form: 1.5A
• Pull Force: 2.83lbs
• Resistance: 0.31 ohms/inch (0.122 ohms/cm)

Hi Shi,

I’ve looked into this for you and I found a great tutorial. Since the wire has very high resistance, the power supply will not react as if it was a short.

In regards to providing correct amperage:

“One simple technique is to look at the target current from the data sheet and then use Ohm’s law (voltage = current x resistance) to calculate the length of wire that is needed to maintain this amount of current based on the power supply you have. Since these wires generally require hundreds of milliamps, I recommend getting a strong lithium-ion battery or use a wall power supply. For example, if I were using the 0.006″ diameter wire, which needs 0.400 Amps, and I have a 5V power supply, I would need a total resistance of 5/0.4 = 12.5 ohms. Since the resistance of this particular wire is 1.3 ohms/in, I would need 12.5/1.3 = 9.5 inches.”

The entire tutorial is here:
https://makezine.com/2012/01/31/skill-builder-working-with-shape-memory-alloy/

Thanks mate. I found out that I may use a battery charge since the internal resistance of a battery is quite small

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