Home FAQ Controller Designs

Introduction

This controller is meant to be an experimental test bench to try out circuit designs and software. It is not designed to be an on-road for-real controller, though my hope is that it will perform well as such. Construction is meant to be as straight-forward as possible: Materials will be (relatively) cheap and (relatively) easy to get, electronics will be bread-boarded where possible, for testing.

Design Goals / Features

  • Voltage: 120V nominal, 175V max (charged pack)
  • Max current: To be determined (see what I can get)
  • Cycle-by-cycle fast current limit
  • Programmable motor current
  • Programmable battery current
  • Programmable low battery voltage
  • Heatsink overtemp current cutback
  • Water cooled

The design: The Straylight MkII is a DC PWM low-side switcher utilizing MOSFETs for switching, and diodes for rectification. The power electronics will be managed by a microcontroller (hereafter: µC). The µC will generate the PWM and partially determine duty cycle.

Current limit: Both absolute maximum and normal current limiting will be accomplished using two high-speed comparators. Both comparators are tied to the output of a current shunt amplifier. Absolute maximum current limit is set by a fixed resistor network. Normal current limit is set by an external D to A that is under control of the µC. If either comparator senses an over-current condition, then the current PWM cycle is immediately stopped via analog circuitry that brings the PWM signal low. Additionally, the microcontroller is interrupted. Current limiting triggered by the absolute max circuit will result in a fault condition.

What happened to the Straylight Mk I?

The Mk I had several design issues that made actually building it rather difficult:

  • The need to cast structural supports for the bus bars in plastic; This has been eliminated, and simple support standoffs are used.
  • Too many holes to drill / tap in the copper bus bars; a heavy-duty PCB is used instead.
  • Attachment of the driver board was tricky, at best; driver board now simply plugs into the (new, didn't exist in Mk I) power board.