A variable output controller for grip heaters or heated clothing costs around $75. We decided to build our own.
We found this schematic at http://www.dprg.org/tutorials/2005-11a/index.html. This is a "Pulse Width Modulation (PWM)" power controller. It is basically an oscillator which switches the power transistor on and off with the relation between on time and off time ("duty cycle") set by the potentiometer position.
In the schematic, the "DC Motor" represents the power load, which actually will be the heating element. Another modification is the potentiometer has a SPST switch which is used to control power to the circuit. In the case of the grip heaters, where the load is permanently connected, a relay is used to connect power to the load (called "+V MOTOR" in the diagram above.) This is done to prevent any possible drain on the battery when the grip heaters are not being used. Finally, the C1 capacitor was changed from 0.1 to 10.0 uF in order to slow the pulse rate down (from about 144 Hz to 1.4 Hz) so as to prevent possible disturbance to the motorcycle electronics.
(To be continued.)
The grip heater controller was built and is in operation. Unfortunately, we forgot to take any photos.
Hopefully, there will be construction photos of the jacket controller...