I am a mechanical engineering graduate that has been learning more about EE through personal Arduino projects and I am relatively unexperienced in Arduino circuit debugging. I have a circuit (see below) that I have been using with an N channel p30n06le mosfet and push button to heat up a strand of nitinol wire (muscle wire)(In my diagram I have an LED in its place).
I have used a 9V battery to successfully heat the wire. To increase the current output and move to larger wires, I ordered two Samsung NCR18650b batteries and soldered two battery cases in series to increase the voltage to around 8.4V. When I substituted the 9V for the battery pack, the wire does not heat.
I am unsure how to debug the circuit and discover the problem. I have measured the voltage across the battery pack and it is around 8.4 V so I assume I soldered correctly. I also have checked to make sure I went positive terminal to negative of the other. Both batteries are new from a trusted retailer and fully charged with an XTar VC2.
I am wondering what other possible errors I could be making in my circuit or debugging methodology that I could perform to find more information on the error?
Any help is appreciated!