Heated car seat

Thread Starter

Chiefee

Joined Apr 10, 2022
4
Hi.

I am currently wiring an electric car seat to use as a gaming/racing seat and have got the electrics working to utilise the movement capabilities.

It also has the heated function too which when bypassing the sensor i can get it to heat up but i need a way of controlling it so it doesnt get too hot. Is there a way i can do this?

Thank you
 

Ya’akov

Joined Jan 27, 2019
5,995
Welcome to AAC.

You can use the sensor you bypassed. Depending on the type you may be able to find an off the shelf thermostat that can handle the job.

On the other hand, I would think very hard about the failure modes if things don’t work as expected. It might not be the best idea to attempt it without using the same circuit the car company used. You might be able to find the controller IC they used, or even a module you could adapt. I would be very circumspect about the attempt, though, considering what failure might look like.

If you choose to do it anyway, please to make sure you include a completely independent TCO (Thermal Cut Out) in series with the element chosen for a safe temperature if the controller fails to control.
 

Thread Starter

Chiefee

Joined Apr 10, 2022
4
When you smell baked ham it is likely overheating.
Do love the smell of baked ham!

I have run 5v through it and it keeps the seat heated at a nice low setting, ideally 7v i imagine would be good. I have read of using a PC psu and using the 12v + 5v rails to make 7v but lots say this is not recommended.
 

MrSalts

Joined Apr 2, 2020
1,818
Do love the smell of baked ham!

I have run 5v through it and it keeps the seat heated at a nice low setting, ideally 7v i imagine would be good. I have read of using a PC psu and using the 12v + 5v rails to make 7v but lots say this is not recommended.
Some older power (late 1990s/early 2000s) supplies will do the 7v trick but there is safety shutdown on the more recent one I tested (~2015).
 

MrChips

Joined Oct 2, 2009
26,472
Car components are designed to run on 12VDC.
What you need is a temperature controlled switch to turn off the power when the temperature reaches a desired setting.
 

MrSalts

Joined Apr 2, 2020
1,818
Car components are designed to run on 12VDC.
What you need is a temperature controlled switch to turn off the power when the temperature reaches a desired setting.
Heaters work at any temp below the max temp, It sounds like 5v works and would SLOWLY drift to an over temp situation vs a much more rapid rise if 12v is used. Why add complexity just because "car components are designed to run on 12VDC"?
 

Thread Starter

Chiefee

Joined Apr 10, 2022
4
Some older power (late 1990s/early 2000s) supplies will do the 7v trick but there is safety shutdown on the more recent one I tested (~2015).
I have a couple stored away somewhere ill have a look to see when they were manufactured.
Heaters work at any temp below the max temp, It sounds like 5v works and would SLOWLY drift to an over temp situation vs a much more rapid rise if 12v is used. Why add complexity just because "car components are designed to run on 12VDC"?
The seat has 2 seperate heat pads. I have now tried wiring the pads in series and it reduces the max temp by quite a bit but doing this one pad is noticably less than the other.

Would something like a potentiometer work?

Ideally having a low/med/high setting is what i am aiming for.
 

MrSalts

Joined Apr 2, 2020
1,818
A simple potentiometer (connected as a rheostat) will just dissipate the extra energy in the potentiometer as heat in another location. Look into a PWM controller. This will take the 12v power and switch it on/off hundreds to thousands of times per second and allow you to adjust the duty cycle of each on vs off ratio. 99% on and 1% off will be almost full power. The invers is almost off. And everywhere in between is possible. In this type of set up, the extra energy is just not delivered anywhere (off) when it is not needed. A much more efficient system. Little controllers are available on eBay and Amazon (among others). Just look for a 12v unit that can handle the max amperage of your seat when powered by 12v. You can power by lower voltage as well so you don't get burnt if you have it turned up to high.
 

shortbus

Joined Sep 30, 2009
9,451
You might be able to find the controller IC they used, or even a module you could adapt.
The seats are usually controlled by the BCM(body control module). And use PWM to set the heat levels to 3 heats levels, mostly, some high end cars may have some sort of temperature/thermostat control but I don't have any experience with high end cars.
 

strantor

Joined Oct 3, 2010
5,980
The seats are usually controlled by the BCM(body control module). And use PWM to set the heat levels to 3 heats levels, mostly, some high end cars may have some sort of temperature/thermostat control but I don't have any experience with high end cars.
The only seats I've tinkered with were from a Range Rover and they were quite complex. A Peltier device was used for both heating and cooling. The seat control module in the seat would not work properly without communication to the driver memory module in the door (automatically changes seat position, mirror angles, and more depending on which driver profile is selected). The heating/cooling would not function without communication to the climate control module in the dash because these features were meant to be selected in a touchscreen I believe.

My 2010 Yukon which had heated seats, also probably would have required communication with a door module, since that is where the heating selection was made on that vehicle. 4 settings (off/lo/med/hi) for both bottom and back. So this probably was also a canbus affair and not a simple switch interface easy to emulate.

I suspect that, unless this seat is from a very early model of vehicle, the factory control module would refuse to behave unless satiated with digital discourse with simulated peers. The specifics of the protocol is surely proprietary and likely not openly hacked. In my case I found it easier to remove the seat control module and make my own. I didn't finish it before I sold the vehicle or I would post details. But an ebay/Amazon PWM power controller should be sufficient, and if you want to go with a closed loop (much safer) you could do this easily with arduino or other microcontroller.
 

Thread Starter

Chiefee

Joined Apr 10, 2022
4
The only seats I've tinkered with were from a Range Rover and they were quite complex. A Peltier device was used for both heating and cooling. The seat control module in the seat would not work properly without communication to the driver memory module in the door (automatically changes seat position, mirror angles, and more depending on which driver profile is selected). The heating/cooling would not function without communication to the climate control module in the dash because these features were meant to be selected in a touchscreen I believe.

My 2010 Yukon which had heated seats, also probably would have required communication with a door module, since that is where the heating selection was made on that vehicle. 4 settings (off/lo/med/hi) for both bottom and back. So this probably was also a canbus affair and not a simple switch interface easy to emulate.

I suspect that, unless this seat is from a very early model of vehicle, the factory control module would refuse to behave unless satiated with digital discourse with simulated peers. The specifics of the protocol is surely proprietary and likely not openly hacked. In my case I found it easier to remove the seat control module and make my own. I didn't finish it before I sold the vehicle or I would post details. But an ebay/Amazon PWM power controller should be sufficient, and if you want to go with a closed loop (much safer) you could do this easily with arduino or other microcontroller.
I think i will bypass the heated sensor module and wire via a PWM. I probably wont be using it much anyway but if the function is there i may as well add a switch for it.

At 5v it works at a nice low level. 7v i imagine will be good to start with but the full 12v it is too intense.
 

shortbus

Joined Sep 30, 2009
9,451
My 2010 Yukon which had heated seats, also probably would have required communication with a door module, since that is where the heating selection was made on that vehicle. 4 settings (off/lo/med/hi) for both bottom and back. So this probably was also a canbus affair and not a simple switch interface easy to emulate.
Never heard of a "door module" before so don't know what one is. Also never considered Off as a real setting before but if it is then I stand corrected on the "3" settings I mentioned before.

The Range Rover is one I would consider high end. And your probably right about ti interfacing with the climate control, since it is also cooling capable. Any of the heated seats I've had(love them because of a bad lower back) just had a form of heating pad in them.
 

MrSalts

Joined Apr 2, 2020
1,818
A new conductive ink is coming on the market soon with positive temp coefficient so it is inherently safe (a max temp is reached at a given supply temp). Another company has heater wires as part of fabrics yarns and woven into the seating fabrics. Third company has elastomeric films (cloth) with various conductivity that allows it to be used as a heater. The whole idea is to integrate functionality into the materials so the feature (heater in this case) is easier to manufacture, no additional parts count, lighter weight, more durable, and customer is still willing to pay for the feature.
 

strantor

Joined Oct 3, 2010
5,980
Never heard of a "door module" before so don't know what one is. Also never considered Off as a real setting before but if it is then I stand corrected on the "3" settings I mentioned before.

The Range Rover is one I would consider high end. And your probably right about ti interfacing with the climate control, since it is also cooling capable. Any of the heated seats I've had(love them because of a bad lower back) just had a form of heating pad in them.
Land Rover door module. That is for the memory functions in the Range Rover. I don't know if other vehicles have this; if they have memory seats, then probably have something similar somewhere, maybe not in the door, I don't know. I was a bit sloppy using that term "door module;" It applies specifically to the memory module, but then I later used the same words to describe the heated seat buttons in my Yukon. I should have said "button cluster" or something to differentiate. I am just assuming that the button cluster was a canbus job, since it seems almost everything is now, and since it doesn't have enough wires coming out to represent all the different things it does. I didn't mean to split hairs over whether or not "off" is a setting; it's just how I think of it, because push once for low, once again for med, once again for high, and once again to return to off.
 
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