Electromagnetic clutch cruise control mosfet or relay ? - Page 1
Forum section: electronics / projects

author: ESXi
author_rank: Regular Contributor
timestamp: March 13, 2020, 09:51:53 pm
content: Ey folks,Completed my car, almost fully disassembled the dashboard and replaced tons parts with excessive wear. All done, but I want to add cruise control to my old car (drive by cable). Got a servo and clutch from a Honda Civic LS 2001 (DENSO MX100300-1190) tested according to manufacturer spec (workshop manual). Tested good, servo and clutch are good.Made a prototype of the unit with a 12volt psu for servo and clutch, controlling the H bridge with a Arduino L298n breakout board. Servo turns fine torque seems good at 100% duty cycle (pwm). But I am not sure if this one is good enough for the job because I cannot find any datasheet of the module with detailed specs. The electromagnetic clutch is a whole other story of course.. How much amperage should it use and what is the best and safest way a relay or mosfet? Mosfet has more cycles but when it shorts, what happens?I have a old Cruise Crontrol kit laying around here Gold Cruise AP500. The thing uses ST mosfets(cannot see which ones have to unsolder them) and has a 15 amperage fuse in it, overkill ?? Or not? I know the electromagnetic clutch is not really power efficient so is this not overkill or is it?The hbridge has two channels max peak amperage of 2a. So one amp per channel, I could only find the L298 datasheet, not sure if it's the same but torque seems to be fine thanks to the worm wheel and gears I guess.I really don't know what the limts are and want to make sure it is done correctly.Insurance wise and shit, doesn't really matter. Just want to control the servo, add pedal switch to avr and if closed circuit is detected by the switch turn of clutch (switch is normally open). Servo control set speed manually or by my gps speedometer project for example read out is 100km/h keep within or disengage clutch when 10-15% off plus or minus. GPS module is a Neo6mv2.Any ideas or tips ?Ps yes. I will add safety switch to turn off all power of clutch and brains if for example avr crahses or f*ck knows what happens.. Just saying.

author: m3vuv
author_rank: Super Contributor
timestamp: March 15, 2020, 11:18:33 am
content: if it was me i would go with a socketed standard 30a car relay,simple cheap foolproof and easy to replace.

author: ESXi
author_rank: Regular Contributor
timestamp: March 17, 2020, 10:04:37 pm
content: Quote from: m3vuv on March 15, 2020, 11:18:33 amThat was what I was thinking as well. Also because mosfets tend to fail shorted. What happens if the mosfet blew up somehow or because of a design fault (high possibility, to be honest). Throttle body is stuck, maybe wide open and I might have a problem (yes). Relays often tend to fail open so that means, clutch is disengaged. Obviously we still have the transmission clutch if its a manual (in my case yes).Even expensive cars car have cc issues. So, I am taking all measurements to make it as safe as possible hard wire off switch interrupt that checks horn & brake pedal switch. Looking at the flow cart of Honda, I might be better off adding the gps speedometer to it and when set if speed is off by x amount of % and tilt sensor is completely horizontal. Disengage clutch, spin servo to back pos for few seconds just in case it was "stuck". Can't see a thing that could go wrong.. I mean yeah the code, there can be a bug or fault. But first need to make the clutch safety test property and build the first prototype.Only con I can see with relay is that it can't switch as fast compared to a mosfet. This may be a issue, I still need to order lots of parts for the prototype because my selfs are empty. But having issues with delivery from AliExpress (taking really long). Even from before Corona virus. I might need to order elsewhere but the price would go up by 80% >.> Breakout boards on Ali 0.56 euro shipped. Here 6 freaking euro!When the concept works, I order premium parts no knock off shit.Some friend was telling me a story a while ago that his boyfriend had a fancy car but was also old. When he was driving on the highway the gas throttle was stuck. He panicked and was stamping on the gas paddle in the hope ot would free up, hmm why not press the clutch. Assuming it was a manual car. Of it was a automatic, why not just turn off the engine.. It is designed to be turned off in case of a emergency..