Doug,
you may wish to research 'ballast resistors' used in automotive ignition systems in times gone by....
The coil pos terminal was supplied with battery voltage, via a 'ballast' resistor, which dropped the supply to circa 9V.
When cranking, the 12v ignition switch supply sent to the starter solenoid was also applied to the coil side of the ballast resistor, bypassing it only when cranking.
You could possibly use a similar approach and also rig up a microswitch for WOT (Wide Open Throttle) which energises a relay to bypass the ballast resistor and supply battery voltage..
Regards.
I'm quite familiar with ballast resistors as I mainly work on classic and vintage vehicles.
I like the micro switch idea, but I think it needs to able to switch over when under loads.
Perhaps if I ran a trigger off the intake manifold? Vacuum operated obviously.
Or with the micro switch idea is there a way I could manage to set it up with less than full throttle to switch it over?
[QOUTE=MikeMl]
How about running the pump in series with an adjustable power resistor (set once) to get the slower speed, and then shorting out the resistor with a FET or relay when full pump output is required? You could use a fancy PWM, but why bother?
The control logic will have to decide when the pump should run at full speed.
A. Cranking is easy. Just use the start contact on the ignition switch as an input.
B. RPM dependent? Use a re-triggerable multivibrator (555) to detect a preset RPM. Triggering signal coming from spark or existing tach pickup.
C. Full throttle? IC comparator (LM339) connected to TPS.
D. Other? [/QOUTE]
Thanks! That's great.
As far as I am aware there isn't a RPM signal involved, which, to me is quite silly. I will have to see some wiring diagrams, I have been trying my best to draw some, but, I'm only used to rather old junk....lucas....