Seat Heat
Hi all... I'm wondering if someone on these ever-so-helpful forums have ever done something like this, and can give me some insight.
My Truck originally had cloth seats in it. I recently found a nice pair of Leather seats, and installed them. The power functions of the seat were difficult to hook up, but with a wiring diagram, I got it all working. Wow, these newer cars aren't easy to repair! it goes like this... the switch for the seat has several switches in one cluster, but the whole assembly only has a 4 wire connector. WEll, I found out, that the switch connects to the CAN bus, and pushing the buttons sends a message over the CAN bus for the onboard computer to receive, which in turn sends a message to the motor control module, that turns on the appropriate motor. This type of system allows different drivers to set up a profile of how they like their seats and mirrors adjusted, and with the press of 1 button, return the seats and mirrors to their preference.
but I digress....
I came here today to talk about the "Heat" function of these seats.
I put the seats in in the summer, and once I got them moving, I considered the job done. Now it's starting to get cold here in upstate NY, and I want the Seat heaters to work.
The wiring diagram shows a setup similar to what I described above. There are 2 rocker switches on the dashboard that turn the Drivers and passenger seat heat on. Each Rocker goes up for HI and down for LOW Heat. The wires lead from these switches to the instrument cluster, which generates the message on the CAN bus for the seat heater to turn on. The heated seat module is mounted elsewhere in the vehicle and has only the following connections in it's wiring harness connector. The CAN bus, Power, Ground, Driver's seat Heater output, and Passenger Side Heater Output.
Mind you, this is from the wiring diagram. My truck wasn't equipped with a heated seat, so none of this exists. All I have are the seats. I am wondering how to procede.
my #1 question. What type of power does the seat need? If just hooking up 12 volts to it is all it needs, then that can be accomplished with a relay, fuse and toggle switch. That's simple, but I fear it may not be that simple.
There is high and low. so perhaps low is fed a 50% duty PWM. and high gets a constant current? That wouldn't be quite as simple, but it's certainly do-able.
The connection to the heat pads built into the seat is simply 2 wires. I just don't want to light a fire under my A$# (literally)
Anyone done this before? I'd love some input. I like to go into a job armed with some information before I start.
(a side story, I once knew a mechanic that said the best way to find a short that's blowing a fuse in a car, is to replace the fuse that keeps blowing with a paper clip, then look for where the smoke is coming from...... I don't want to be that guy)
My Truck originally had cloth seats in it. I recently found a nice pair of Leather seats, and installed them. The power functions of the seat were difficult to hook up, but with a wiring diagram, I got it all working. Wow, these newer cars aren't easy to repair! it goes like this... the switch for the seat has several switches in one cluster, but the whole assembly only has a 4 wire connector. WEll, I found out, that the switch connects to the CAN bus, and pushing the buttons sends a message over the CAN bus for the onboard computer to receive, which in turn sends a message to the motor control module, that turns on the appropriate motor. This type of system allows different drivers to set up a profile of how they like their seats and mirrors adjusted, and with the press of 1 button, return the seats and mirrors to their preference.
but I digress....
I came here today to talk about the "Heat" function of these seats.
I put the seats in in the summer, and once I got them moving, I considered the job done. Now it's starting to get cold here in upstate NY, and I want the Seat heaters to work.
The wiring diagram shows a setup similar to what I described above. There are 2 rocker switches on the dashboard that turn the Drivers and passenger seat heat on. Each Rocker goes up for HI and down for LOW Heat. The wires lead from these switches to the instrument cluster, which generates the message on the CAN bus for the seat heater to turn on. The heated seat module is mounted elsewhere in the vehicle and has only the following connections in it's wiring harness connector. The CAN bus, Power, Ground, Driver's seat Heater output, and Passenger Side Heater Output.
Mind you, this is from the wiring diagram. My truck wasn't equipped with a heated seat, so none of this exists. All I have are the seats. I am wondering how to procede.
my #1 question. What type of power does the seat need? If just hooking up 12 volts to it is all it needs, then that can be accomplished with a relay, fuse and toggle switch. That's simple, but I fear it may not be that simple.
There is high and low. so perhaps low is fed a 50% duty PWM. and high gets a constant current? That wouldn't be quite as simple, but it's certainly do-able.
The connection to the heat pads built into the seat is simply 2 wires. I just don't want to light a fire under my A$# (literally)
Anyone done this before? I'd love some input. I like to go into a job armed with some information before I start.
(a side story, I once knew a mechanic that said the best way to find a short that's blowing a fuse in a car, is to replace the fuse that keeps blowing with a paper clip, then look for where the smoke is coming from...... I don't want to be that guy)
Comments
And regarding hi/low seat heat: Sure you could get fancy with PWM and all that. I humbly suggest that if you want lower heat, you can do it simply with a 556 timer tripping a relay to vary the "duty cycle" like intermittent wipers. Switch the heater off with a relay every 20 seconds for an adjustable period. Your warm butt won't know the difference!
Check the resistance of the two wires to the seat. I think its just a length of conductor with a resistance such that it draws a certain (low) number of watts, and at 12 volts it can only get so hot. This was also the case with the pizza delivery heated bag I looked at. Cheap and simple. But I was afraid of getting a short in my shorts, as I did not have the special heat resistant coating wire, so that's as far as I got.
Least you did not end up with a couple of fried eggs. Hhmmm hard boiled or maybe sunny side up? 12V @ 30 amps could be a bit warm I guess...
FF
But I think if the resistance works out right, one could determine if the built in seat heater is going to cook or not at 12 volts? I would think that a stock electric seat unit would be safer than my snarl of random wire.
http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm
I didn't think about that. For something like this, The duty cycle is more important than the Period. I could lengthen the Period out to 20 seconds as you suggest, and simply use a relay and a means of timing, such as a 556 or a microcontroller.
I may throw a Propeller into it, it'd certainly be overkill, but it's a one off project, not something I'm going to mass produce. I got my hands on the original heated seat switches, and a pinout diagram of the switches. They have a high and low indicator LED, each having their own input, so I could easily drive those LEDs with the Propeller as well.
This is the Pinout of the switch :
Cavity Circuit Function 1 P81 20TN/OR DRIVER HEATED SEAT LOW INDICATOR DRIVER 2 E33 20OR ILT-DIMMING CENTER BEZEL/HEATED SEAT SWITCHES 3 Z968 20BK GROUND 4 F21 20PK/DG FUSED IGNITION SWITCH OUTPUT (RUN-START) 5 P83 20TN/WT DRIVER HEATED SEAT HIGH INDICATOR DRIVER 6 P7 20LG/YL DRIVER HEATED SEAT SWITCH MUX
The "Circuit" cross references it to other wiring diagrams for this vehicle, it also mentions the wire gauge and color insulation.
The only "problem" which I believe the Propeller can overcome. Is the "MUX" I'd have to decode this signal with a logic analyzer or such and figure out what data to listen for that indicates a button press.
definitely, once I measure the resistance of the heater elements, and/or measure the current draw when I wire it directly briefly for testing purposes. I'll add a little overhead and fuse it properly. I'll also need to filter the power to the Propeller heavily. The automobile electrical environment certainly can be described as "Harsh".
I'll report back with news and photos as I continue this project. and Thanks for the help guys!