Have been doing a little bit of research and thinking, dangerous I know.
One of the reason I want to create a PWM motor controller is to limit the noise that these motor make when driven by very low PWM frequencies that the MS3 PWM O/P’s provide as well as utilising it in a returnless fuel setup.
One of the problems is that the MS3 and or TunerStudio MS has a limited set of output frequencies (11.1Hz to 250Hz) to drive motors in closed loop PWM control. From my research frequencies required to make the motors run quietly (hopefully in the upper audio frequencies) and still maintain sufficient torque and not overheat, vary wildly depending on the motors electrical and mechanical characteristics.
A test I did a year ago using MS3 resulted in a awful lot of noise from the motors using the MS3. Like my fuel pump was a coffee grinder and the radiator fan was not much better either!
The implementation would look at the duty cycle of the input (from MS3) and switching the output to the motor at the same duty cycle but at a user selectable frequency (possibly at a multiple of input frequency). I won’t go into to many details as I’m still thinking of the design plus I’ll be doing some prototyping shortly, but it will:
- be a micro controller based design
- have high speed opto-coupling of the I/P (very important if there is a problem with the O/P you don’t want high voltage fed back into the MS3)
- have user selectable PWM switching frequencies either as multiples of I/P frequency or it’s own configurable frequencies
- it will work out the dwell (duty cycle) of the I/P from the MS3
- it will either have medium current IGBT or MOSFET O/P transistors.
- be contained in its own splash proof case
- mounted close to the motor to minimise the EMI from the high frequency current wires
At this stage I’m just investigating and prototyping…