Thank you for explaining that, I understand how it works much better now. I'm unable to use the AWD normally via the switch as there's problems with ESP that I'm not interested in fixing. At this point, I'm going to install a switch in my dash to give that coupler 12V directly and I'll just be mindful of when and how long I keep it on. I don't need AWD very often, only to power through snow or up a steep slippery hill etc. I own a parts SX4 so if something goes wrong I have a replacement coupler handy.This is not about the transfer case. AWD is applied at the coupler, which is at the rear differential. The coupler is an electrically activated clutch. OF course one can switch 12V directly to the coupler coil but I'm not sure of the time that the coil can survive with the full 12V. IN Auto 12V is applied in a duty cycle mode, that is, equivalent to reduced voltage based on conditions. In lock mode, I have not tested the actual duty cycle but if I were the designer, I would make it proportional to throttle. So...while your proposal has been also in my head at times, I would not risk abusing the coil.
Looking for the electrical diagram....will post later.
EDIT: everything here http://www.avigex.ca/sx4/AWDtrouble.pdf
NOtice there is a temperature sensor that limits the amount of AWD . This protection would be inactive if a direct 12V feed was installed....
yes and no.Thank you for explaining that, I understand how it works much better now. I'm unable to use the AWD normally via the switch as there's problems with ESP that I'm not interested in fixing. At this point, I'm going to install a switch in my dash to give that coupler 12V directly and I'll just be mindful of when and how long I keep it on. I don't need AWD very often, only to power through snow or up a steep slippery hill etc. I own a parts SX4 so if something goes wrong I have a replacement coupler handy.
From your description of how the clutch engages, I understand that the voltage you apply to the coil effects how much pressure the clutch engages with. So if the car isn't moving or under load and there's a full disproportionate 12V on the coil, it will just heat things up and cause unnecessary wear and heat. If I'm understanding this right, when there is no voltage on the coil it should be completely disengaged? So the 4WD control module basically modulates how much voltage the clutch coil requires in relation to variables like the AWD switch position, load, speed, coupler temp, wheel slip, etc. I see how the 4WD module maximizes the life of the coupler.
Am I on the right track here?
This is an 09 SX4 AWD Manual. ESP doesn't work because several sensors are missing like the one in the center of the car right above the airbag control module. There's a instrument cluster from an automatic AWD in there that doesn't even have an ESP light and I'm sure that doesn't help anything. The parts car is an 07 SX4 and it turns out that the only difference I could find between model years is armrests and the gforce sensor for ESP. They're different sensors with different wiring unfortunately.yes and no.
Applying 12V directly to the coil will kill it in pretty short order due to over heating. I would expect it to last about 5 minutes. The controller varies the amount of current the coupler draws to control its "clamping" force. Its like a light dimmer, voltage stays the same, but the current gets varied.
Why not fix the ESP issue? what symptoms do you have? if you have a parts car then you have sensors, tone wheels and all the necessary bits to fix it.
I can't fathom why you say "i'm not interested in fixing it" when you seem willing to destroy a rather expensive AWD clutch pack by "hot wiring" it directly to a 12V supply rather than correcting the root cause of your lack of AWD.
Constructive comment.you obviously don't understand how the 4WD system works on these models, its fully electronically controlled and has varying torque split front to rear depending on wheel slip detected.
its not just a "switch"
Yeah....I have searched the shop manual line by line in hope of finding the exact values of full current or resistance of the coil....to no avail.It's going to be a switch and current potentiometer pretty soon.
this is the one, 20A rating, i'm picking the first one won't handle the inrush current in the coil and may fail.
Thanks for the help. I just bought 2 of the 20A ones.this is the one, 20A rating, i'm picking the first one won't handle the inrush current in the coil and may fail.
the good thing with mosfets, running lower currents on higher powered devices causes no issues and they will run cooler. I would suggest fitting a decent spike suppression capacitor across the power input, car electrics are notoriously "noisy". You can use a decent radio "filter" designed for aftermarket amps or radios, they are cheap and will help protect the mosfet from damage from spikes caused by other stuff switching off and on like the AC and fans etc.Thanks for the help. I just bought 2 of the 20A ones.
I also bought this so I can monitor the amps.
I'll update this in a couple weeks with my results when the parts come from China and I get it installed.