As a learning exercise, I am trying to control a 12VDC/0.18A computer fan with a thermistor. As I am planning the circuit (and I certainly can be wrong in my calculations), I plan to have a 12V power source (8AA batteries in series). I am trying to use a PN2222 transistor to control the fan's speed. According to my calculations, I would need 6mA into the base of the transistor to get the 180mA needed to run the fan at (or close to) full speed. So, then to control the speed from there, i.e. clamp down the current going to the base to reduce the current into the fan, I have placed a 5-100K thermistor in line with a 2K resistor.
Connections: Negative rail connected to Emitter and 2K Resistor which also connects through thermistor to base. Collector is connected to negative side of fan. Positive rail connects to positive terminal of fan.
I believe I have included all the pertinent information, but if I left something out, I'll be happy to add more.
So, the problem I am having is that the fan doesn't even turn. I have connected the fan directly to the battery source, and the fan turns. I have started some basic troubleshooting, but found that I am reading 0V across the 2KR (1.9K pictured). So, I guess my question is what am I missing here? Why can I not get the fan to turn in this circuit, and I am sure it is probably something stupid.