What should I base the maximum speed limit on?
The upper limit must not exceed the engine manufacturer's rated and full-load speed; if the limits of the driven equipment are lower, those are the determining ones. For example mud pumps typically turn at 100-200 rpm and since there is a gear or belt in between, the upper limit on the engine side is chosen according to that ratio. On a 4-pole generator 50 Hz means 1500 rpm, and the limit is set according to that value.
Read three sources together when setting the upper limit:
- Engine: the rated speed and continuous operating speed in the manufacturer's catalogue. There is no reason to go above them.
- Driven equipment: the speed allowed by the pump, alternator or gearbox. On a piston pump the flow is directly proportional to speed; unnecessary speed means pumping for nothing and wear.
- Frequency: on a generator f = (speed x poles) / 120. On a 4-pole alternator 1500 rpm gives 50 Hz, on a 2-pole one 3000 rpm gives 50 Hz.
On the GS740-3P the limit is taught by running up to that speed with the potentiometer and briefly touching the blue wire to GND. The function of this limit is to restrict the actuator travel; it is not an engine overspeed protection. Overspeed protection is typically a separate arrangement belonging to the engine's own protection chain, tripping at 10-20% above the rated speed, and it is not present in these kits.
Full article: Electronic speed and throttle control on a diesel engine