I am trying to build a simple motor controller circuit. I have a lithium ion battery (7.4 volts, 20C discharge, 800mAH capacity) that powers the motor and I am using an adjustable voltage supply on the MOSFET gate.
I have the circuit set up according to the image below:
The motor pulls about 3 Amps at 7.4 volts and the MOSFET is a logic level enhancement mode n channel MOSFET. The gate threshold is about 2.5v and it can handle a continuous current up to 20 amps.
MOSFET Datasheet: https://www.vishay.com/docs/91021/91021.pdf
The MOSFET should start to turn on at 2.5V but when I probe the drain of the MOSFET with 3.3v at the gate I still see 7.4V.
This exact same setup works perfectly if I just replace the motor with an LED. I know the motor is working too. The MOSFET just does not seem to pull its drain low if the motor is connected, even with a gate voltage present.
Why doesn't my circuit work with the motor?