1983 Porsche 911 SC Targa

Wednesday, July 25, 2012

Soliton 1 Motor Controller

My controller arrived, and it is quite an impressive piece of hardware. It is 33 lbs (15 kg) of beautiful cast aluminum. The controller is rated for 300 kilowatts of continuous power (400 HP). I will not be pushing the limits of the controller, but it doesn’t hurt to oversize the controller and leave a little margin.

The controller will be mounted above the motor and is wired between the battery pack and the motor.

The controller’s job is to regulate how much of the battery pack voltage and current is sent to the motor, and to do so as efficiently as possible. Modern transistors are very efficient when they are fully on or fully off, but they tend to generate a lot of heat when they are partially on. The controller continuously connects and disconnects the motor to the battery pack. The switching speed is fast enough (8,000 cycles per second) that the motor does not react with a noticeable pulse each time the battery is connected and disconnected. The motor only “sees” an average voltage that depends on the how long the battery stays connected and how long the battery is disconnected within each switch cycle. For example, if the controller is on half the time, and off half the time, then the motor “sees” 50% of the battery voltage. If the controller stays on for 10% and off for 90% of each switch cycle, the motor will operate the same as if 10% of the full battery voltage were applied. The duty cycle is set by the position of the accelerator pedal.


  1. What happens when it latches (electrically or mechanically) at 100%? Are you planning a real EMO or just a wild ride?


    1. There is a progression of options to protect the driver in the very unlikely event the controller fails full on.
      1) Turn the ignition switch to off to open the internal controller contactor.
      2) I will have an external contactor wired to an emergency off button to disconnect the battery pack. Interrupting a high current line is no easy task, and the contactor could weld shut, which is why I would like to have two chances.
      3) The last resort would be to press the clutch and pop the transmission out of gear to disengage the motor from the transmission. The motor will certainly over rev and destroy itself, but the driver could walk away. Some conversions use a solid coupler between the motor and transmission, and safety was a key reason I kept the clutch.