Powering a PWM valve with 24V PWM

[Jamie Janke]

Well well well. You are certainly being a great help. Problem is at the moment I can't answer all your questions but will certainly endeavour to get all the info.

I know the Jd has unlimited movement

I believe they are switched highside

Wattage and resistance unknown ATM

I believe it's just the PWM SIGNAL

No idea about the dither.

MAX duty cycle is 30%

I believe both solenoid are in a dormant state when machine is going straight.

Frequency unknown at the moment.
I will attempt to find more information

 

[alec_t]

Here's a first draft of the interim, fixed duty-cycle circuit.
It comes with no warranty .

A standard '555 based oscillator generates about 270Hz and the pot allows adjustment of duty-cycle from ~1% to ~40%.
The coils are high-side driven in this circuit. The MOSFET shouldn't need a heat-sink and its type is not critical.
Wiring to the valve coils should probably be screened to avoid any interference with the CAT's ECM.
Depending on the 12V and 24V power supply characteristics and the dozer electrical system the circuit may need additional decoupling and transient suppression components.

 

[alec_t]

..... and here's a first draft of the fully-fledged PWM driver if you find you need to use a wheel angle sensor for proportional rather than bang-bang control. I have assumed the angle sensor is a Hall effect type operating on a 5V supply and providing either a 0V-5V analogue output or a 5v PWM (~ 1kHz) output. The same caveats as for the post #22 circuit apply.

U1a and U1b derive downward going and upward going ramp signals D, U respectively, according to how far the angle sensor output varies from its mid-point value. These signals are compared (by U2a, U2b) with a triangle wave signal produced by U1c and U1d to provide PWM signals Lpwm, Rpwm which drive push-pull stages Q1-Q4 and hence high-side P-MOSFETS M1,M2 to power the steering valve coils Lcoil, Rcoil. A pot provides scaling of the angle sensor signal and so allows adjustment of the maximum duty-cycle of the coil drive.
It would be advisable to test a prototype circuit in the lab so that component values can be tweaked prior to installation on the CAT.

 

[Jamie Janke]

Hello Alex.

Thank you for your assistance with my GPS project. Your expertise has been very helpful. Furtunetly and unfortunelty a respected Autosteer company (Farm Scan) has taken this project on themselves. I am only going to help now with some technical Data for the Cat Machine itself and then the install but as they are local to where the machine is being predelivered it has worked out good that their electronics gurus have been able to tap into the steerin arm signal circuit and feed the ECM that way and let the ECM scontinue to steer the machine. I have a lot of interest in this but unfortunelty it is well beyond my understanding at the moment.

I just wanted to take the time to say thanks for your efforts with trying to help me out. I must say i have looked at your last 2 posts and really i am stumped as to how to understand it all but hopefully in time i will better understand.

Kind Regards Jamie.

 

[alec_t]

Good luck with the project. Keep us posted.