I'm working on a remote start system for an older gm diesel vehicle and so far everything has worked great, but I've hit a stump that I just cant figure out.
The engineers who designed the ignition switch of my truck though it would be a good idea to run starter solenoid power though the ignition switch itself, and they didnt bother to include a Starter Relay until 96, my system is designed to work on pre 96 vehicles so I dont get the luxury of tapping into that relay for starter engagement. The solenoid on the starter itself that engages the starter to the flywheel is what I need to control and based on the fuse ratings and wiring diagrams from the vehicle I believe the load wont exceed 40A for the starter engagement, and keep in mind this will only be engaged for maybe 20 seconds max per cycle, and being a remote start it will have irregular cycling.
Now for the ignition portion, the power flows from the ignition switch in the RUN position to a few different systems, ignition, fuel injection, lights, gauges, and transmission. Using the wiring diagrams, I calculated 85A max that will flow through the Ignition portion of the circuit. Obviously this is an absolute max and it will certainly never reach that load but all of the listed systems are run from a singular wire that comes off the ignition switch, the PINK wire in the diagram.
I've designed my circuit to handle the starter load and ignition loads separately, but my problem is finding relays capable of that current that are actually in stock through JLCPCB. I plan on making these in small batches IE 20-30 at a time based on demand, and I'm trying to not only ensure long term reliability but also future proofing as well. There are suitable options that I've found but they only have maybe 200ish in stock max and I don't want to find something that works just to have to change it next time I go to order more.
I've considered using mosfets as they are much cheaper than the relays im looking at and are more available, but im concerned about heat management. safety, and long term reliability of using mosfets over relays.
TLDR-
-I need to reliably and safely switch power to the PINK and PURPLE wires on the diagram
-PURPLE wire load is 40A abs max
-PINK wire load is 85A abs max
My question to anyone reading this is how would you design this circuit to safely and reliably switch the high current (40A for starter and 85A for ignition) with interest of keeping cost down, would you use MOSFETS or RELAYS, and why would you go that route?
The engineers who designed the ignition switch of my truck though it would be a good idea to run starter solenoid power though the ignition switch itself, and they didnt bother to include a Starter Relay until 96, my system is designed to work on pre 96 vehicles so I dont get the luxury of tapping into that relay for starter engagement. The solenoid on the starter itself that engages the starter to the flywheel is what I need to control and based on the fuse ratings and wiring diagrams from the vehicle I believe the load wont exceed 40A for the starter engagement, and keep in mind this will only be engaged for maybe 20 seconds max per cycle, and being a remote start it will have irregular cycling.
Now for the ignition portion, the power flows from the ignition switch in the RUN position to a few different systems, ignition, fuel injection, lights, gauges, and transmission. Using the wiring diagrams, I calculated 85A max that will flow through the Ignition portion of the circuit. Obviously this is an absolute max and it will certainly never reach that load but all of the listed systems are run from a singular wire that comes off the ignition switch, the PINK wire in the diagram.
I've designed my circuit to handle the starter load and ignition loads separately, but my problem is finding relays capable of that current that are actually in stock through JLCPCB. I plan on making these in small batches IE 20-30 at a time based on demand, and I'm trying to not only ensure long term reliability but also future proofing as well. There are suitable options that I've found but they only have maybe 200ish in stock max and I don't want to find something that works just to have to change it next time I go to order more.
I've considered using mosfets as they are much cheaper than the relays im looking at and are more available, but im concerned about heat management. safety, and long term reliability of using mosfets over relays.
TLDR-
-I need to reliably and safely switch power to the PINK and PURPLE wires on the diagram
-PURPLE wire load is 40A abs max
-PINK wire load is 85A abs max
My question to anyone reading this is how would you design this circuit to safely and reliably switch the high current (40A for starter and 85A for ignition) with interest of keeping cost down, would you use MOSFETS or RELAYS, and why would you go that route?