This page describes a controller that I built in 1996 for a 12.5KW diesel motor/generator set.
The generator is driven by a 2 cylinder Chinese diesel engine.
In order to keep the generator's output frequency near 60Hz over the full load range, I designed
a controller to adjust the throttle position to keep the engine speed near 1800 RPM.
The picture above shows a frontal view of the finished system (click on it for a larger image).
The controller's circuit board is housed in a black box located in the upper right corner of the frame.
The throttle positioner is housed in a blue box located down on the runner. You can see the actuator
cable running from the positioner box through some pulleys up to the throttle lever on the injector body.
The box in the center of the upper portion of the frame houses gauges (DC volts, DC amps, RPM, engine temperature and
oil pressure) along with the starter switch, heater switch and kill switch.
The heart of the control system is a Basic Stamp II microcontroller.
(If I were to embark on this project today I would probably use the ZX-24 instead because it is a much more
powerful controller and yet is Stamp-compatible.
See the ZBasic and ZX-24 Site for more information.)
There is a magnetic pickup positioned near the flywheel teeth which provides a pulse train proportional
to engine speed. A linear actuator (a stepper motor that moves a threaded shaft axially through the
motor body) is used to effect throttle positioning. The controller samples the engine speed and then
adjusts the throttle position attempting to keep the RPM relatively constant.
In order to be able to display an indication of the generator's load, a current transformer was made for
each power leg by winding some turns of enameled copper around a pseudo-toroid core made of steel. The voltage from the
center-tapped winding is conditioned by an op amp circuit and then fed to an analog-to-digital converter. Using empirical
data, code was written to perform an approximate piecewise linear transformation of the current transformer signal to a
current value in amps.