MoTeC Global Forum

I need to PWM control the solenoid in my power steering rack from my M800 based on road speed. The factory control unit provides a voltage to the solenoid which is 5 4V at rest and decreasing as speed increases. My understanding is the solenoid doesn't like to see 12V.
Any suggestions on a way to approach this

Thanks
Daniel

The ignition outputs are pulled up to about 5V, so if you had one of those spare you could use that for your PWM. Otherwise you could use one of the generic aux outputs in lowside drive mode with an external 5V pull-up.

Edit: actually I might have read your question wrong. Do you want to drive the solenoid directly or are you sending PWM to the existing controller?

Thanks for the info
I'm using a CDI-8 so I have free ignition outputs so what you suggested sounds like a perfect solution
Your assumption was correct I want to drive the solenoid directly and delete the original controller

Sorry, I was assuming you were wanting to PWM to some sort of controller. If you want to drive the solenoid directly you will first need to measure its resistance to check if its current is within want an aux can supply.

Also, I suspect the "5V" that you are measuring is false due to PWM. If you unplug the solenoid does it have constant 12V on one pin?

The voltage values came from the workshop manual

The ignition outputs have current limited high-side drive with a maximum current of 40mA at 6V for Ignition purposes. What voltage rating is the solenoid in the car? We need more information on the device and how its wired to give you a better answer.

All I have is this wiring diagram

And this information from the workshop manual. The solenoid is in the power steering rack itself.
I do also have voltages for specific speeds

You can control this several ways,

Leave the PPS computer there and use the ECU low-side driver output to mimic the speed sensor.

Remove the PPS computer,
W-R (pin2) is most likely constant +12V and W_G ( pin5 ) is PWM to ground. Use a ECU output to ground using PMW mode connected to W-G and +12V to W-G.

To determine what ECU output can be used.

With the PPS computer powered up, measure from pin 2 to ground to confirm the voltage at pin 2.

With the PPS removed, Measure across 2 and 5 to get the PPS solenoid resistance and work out the current using the previously measured voltage.

The reason for the strange voltage measurement is if you are using a multi meter, measuring voltage across that point at that given speed, a duty cycle PWM could look like a 4.8V signal due to the multi meter circuitry.

Just remembered M800 cant do frequency output based on speed so cannot use mimic Speed sensor option