This is a DC motor controller I designed for a 1kW electric powered esky. The motorised esky was originally produced by a Canadian company called Cruzin Cooler.

As a present to himself, a friend of mine purchased this unit for his 40th birthday (he is a bit of a Bogan, Harley rider etc). The problem is, this product was designed in Canada. The company put a high powered controller inside a very insulated Esky inclosure. On a 42C summer day in Adelaide, the result was the controller's MOSFET driver shortcircuited and drove the motor at full power. The result of this nearly injured his son when he was using it. Long story short, my friend gave me esky to see what I could do with it. I designed a new controller for it.

The old controller simply varied the current supplied to the motor. This caused the drive transistors to over heat and fail short (ie: the transistors would short out and supply full power to drive motor). My design supplied power to the motor as a pulse width modulated current supply. The idea of this design is it made the transistors operate as a cooler temperature. This was the key, because in Adelaide, summer temperatures reach up to 45C. They can not fail when it gets hot.

Along with a better design for a hot climate, I added some safety features - "keep'in Thomo safe !":

• Tilt detector in the event the esky flips due to operator applying to much power to motor. Reaction time: Instant.
• Short out detector in the event the switching transistors short out. Reaction time: 300ms.
• Brake sensor motor cut (motor will only be powered when throttle is 0% after brake disengaged).
• Temperature monitoring of controller/power supply, switching box and motor. >= 50C RED warning light on status light. >= 70C esky will power off.
• Status LED on cluster:
  • Red flashing: Temperature warning.
  • Green flashing: short out detector operational.
  • Solid green: Logging mode (maintenance mode)
  • Flashing blue: brake engaged.
• Kill switch and kill button on cluster.
• Filtered throttle acceleration response. 10% per 100ms. (Nb/ If controller delivered instant current to motor from battery, it would flip Esky and throw rider onto ground !)
• Esky shutdowns down after 5 minutes of throttle inactivity.
• Status reporting via serial port.

This is my first experience in designing circuitry that deals with a lot of power and a lot of heat. Below are more pics from this project.

Power supply PCB:

The switch box (with two power MOSFETS inside):

Controller and power supply enclosures:

Testing phase:

Controller PCB: