Temperature Controller

by Sidney Kantor

The Vision

My friend, who was living the van life, had a solar setup in his vehicle and needed a way to maintain the temperature of his batteries in the winter to ensure they were at a safe temperature to take a charge so I came up with a temperature controller to automatically turn on/off a heater based on the temperature of the batteries.

Schematic

This was a fun little circuit to design. I decided to leave out the microcontroller and do things old school using discrete components. It's a fairly simple design. I used a thermistor to determine the temperature of the batteries, an operational amplifier configured as a schmitt trigger to allow for some hysteresis at the temperature setpoint, a MOSFET for the switch, an LM7805 voltage regulator and an LED that lights up when the temperature controller is on. Also, note that my friend included a fuse inline with the temperature controller when it was installed.

The hand drawn initial schematic.

The protoboard populated with the components.

The temperature controller wired up.

Stress testing the temperature controller at maximum rating.

The temperature controller enabled.

The final product ready for delivery :-).