I'd like to apologize in advance for the length of this question - I tried to get all the details into one post, and it got very long.
Hello everyone - this is my first post here and honestly, I'm a bit apprehensive. As I've searched through similar threads trying to find my answer, I come across folks claiming to be "noobs", who then launch into a litany of tech speak that quickly has my head ringing. Among my circle of friends, I'm "the smart tech guy", and these so-called noobs, make me look like a pre-schooler. I'm stunned at the vast array of topics that people on this board are experts on - truly impressive.
But enough of that - here's my issue: I have a solenoid in my car that I would like to control manually via a PWM controller. This solenoid controls hydraulic pressure to a clutch that controls the rear wheel drive in my AWD transmission. Under normal operation, the car has a 70%-80% front wheel drive bias, but if you really get on the throttle, the transmission computer (TCM) will send some of the power to the rear wheels to prevent wheelspin. This all works well in normal everyday driving, but the car sees some amateur competition on weekends where I ask it to work it's hardest on gravel, mud, snow and all manner of slippery surface. When pushed this hard, the AWD system exhibits some troublesome lag. The front wheels can sometimes spin for as much as 1.5 seconds before the rear lockup is called for - usually very abruptly. This hurts performance in two ways - first, by the time the rear wheels join in, I'm well past the place where I needed them, and second, when they lock up abruptly, it upsets the balance of the car.
Here's what I know about the solenoid/TCM:
The solenoid is driven by a 12vDC PWM signal operating at a fixed 50hz
The solenoid's impedence is 10 - 17Ω according to the factory service manual
I have not been able to determine solenoid current, but believe it to be around 700mA at 95% duty cycle.
0% duty cycle = full rear wheel lockup (50/50 front-rear torque split)
100% duty cycle = no rear wheel lockup (front wheel drive)
The TCM will vary the duty cycle to the solenoid anywhere from 5% to 95% depending on throttle position and vehicle speed.
I've already put a switch and a 17Ω "dummy load" in line to fool the TCM - basically killing power to the solenoid and locking the car at a 50/50 torque split. This works, but in an effort to improve performance, and learn some new tricks along the way, I'd like to build a PWM controller that will allow me to dial in as much rear wheel traction as necessary.
I stumbled across a schematic and build plans for a 12vDC PWM controller aimed at quieting down PC fans at this site.
Using the stripboard layout, and some of his suggested alternate parts to change frequencies and run higher loads, I built a working 60hz PWM controller. It controls a PC fan quite nicely, but when I tried to hook it up to the car, I ran into a problem. (apologies - this is where my utter lack of electronics training is going to reveal itself) In cpemma's schematic, the MOSFET is is controlling the fan via the path to ground. I understand this is perfectly reasonable, but I don't have (easy) physical access to the solenoid's ground wire. It's wrapped up in an aluminum transfer case and surrounded by 12qts of transmission fluid.
What I think needs to happen, is to use the MOSFET to control the current TO the solenoid instead. However, looking at schematics that do switch the 12v line to the solenoid, like this 555 version, I see that the FET symbol is different. Is this the difference between N-channel, and P-channel MOSFETS?
I'm reading through the fantastic electronics classes at the top of this forum, and understand the concept of field effect transistors, but implemetation and actual operation are still a bit fuzzy.
The MOSFET I chose was the IRF630B which is an N-channel version. If I swap to a P-channel MOSFET and reroute the signal to the positive side of the solenoid, will this fix my problem?
Could it possibly be this simple? I doubt it.
Have I drastically underestimated the complexity of what I'm attempting? Very likely.
School me - I'll listen!
Hello everyone - this is my first post here and honestly, I'm a bit apprehensive. As I've searched through similar threads trying to find my answer, I come across folks claiming to be "noobs", who then launch into a litany of tech speak that quickly has my head ringing. Among my circle of friends, I'm "the smart tech guy", and these so-called noobs, make me look like a pre-schooler. I'm stunned at the vast array of topics that people on this board are experts on - truly impressive.
But enough of that - here's my issue: I have a solenoid in my car that I would like to control manually via a PWM controller. This solenoid controls hydraulic pressure to a clutch that controls the rear wheel drive in my AWD transmission. Under normal operation, the car has a 70%-80% front wheel drive bias, but if you really get on the throttle, the transmission computer (TCM) will send some of the power to the rear wheels to prevent wheelspin. This all works well in normal everyday driving, but the car sees some amateur competition on weekends where I ask it to work it's hardest on gravel, mud, snow and all manner of slippery surface. When pushed this hard, the AWD system exhibits some troublesome lag. The front wheels can sometimes spin for as much as 1.5 seconds before the rear lockup is called for - usually very abruptly. This hurts performance in two ways - first, by the time the rear wheels join in, I'm well past the place where I needed them, and second, when they lock up abruptly, it upsets the balance of the car.
Here's what I know about the solenoid/TCM:
The solenoid is driven by a 12vDC PWM signal operating at a fixed 50hz
The solenoid's impedence is 10 - 17Ω according to the factory service manual
I have not been able to determine solenoid current, but believe it to be around 700mA at 95% duty cycle.
0% duty cycle = full rear wheel lockup (50/50 front-rear torque split)
100% duty cycle = no rear wheel lockup (front wheel drive)
The TCM will vary the duty cycle to the solenoid anywhere from 5% to 95% depending on throttle position and vehicle speed.
I've already put a switch and a 17Ω "dummy load" in line to fool the TCM - basically killing power to the solenoid and locking the car at a 50/50 torque split. This works, but in an effort to improve performance, and learn some new tricks along the way, I'd like to build a PWM controller that will allow me to dial in as much rear wheel traction as necessary.
I stumbled across a schematic and build plans for a 12vDC PWM controller aimed at quieting down PC fans at this site.
Using the stripboard layout, and some of his suggested alternate parts to change frequencies and run higher loads, I built a working 60hz PWM controller. It controls a PC fan quite nicely, but when I tried to hook it up to the car, I ran into a problem. (apologies - this is where my utter lack of electronics training is going to reveal itself) In cpemma's schematic, the MOSFET is is controlling the fan via the path to ground. I understand this is perfectly reasonable, but I don't have (easy) physical access to the solenoid's ground wire. It's wrapped up in an aluminum transfer case and surrounded by 12qts of transmission fluid.
What I think needs to happen, is to use the MOSFET to control the current TO the solenoid instead. However, looking at schematics that do switch the 12v line to the solenoid, like this 555 version, I see that the FET symbol is different. Is this the difference between N-channel, and P-channel MOSFETS?
I'm reading through the fantastic electronics classes at the top of this forum, and understand the concept of field effect transistors, but implemetation and actual operation are still a bit fuzzy.
The MOSFET I chose was the IRF630B which is an N-channel version. If I swap to a P-channel MOSFET and reroute the signal to the positive side of the solenoid, will this fix my problem?
Could it possibly be this simple? I doubt it.
Have I drastically underestimated the complexity of what I'm attempting? Very likely.
School me - I'll listen!