Heating BMW seats (using BMW parts) (1 Viewer)

[LA Z]

Take a look at these MOSFETs.
They're for automotive applications, cheap and handle more power than what the heat pad needs.

Cooling them shouldn't be an issue, even at 10A it only needs to dissipate less than 1/2W and
they'll be more than happy to turn on and off millions of times in complete silence.

https://www.infineon.com/dgdl/sg-auto40v.pdf?fileId=5546d462533600a4015356a094a52ca6

 

[NoLys1776]

Take a look at these MOSFETs.
They're for automotive applications, cheap and handle more power than what the heat pad needs.

Cooling them shouldn't be an issue, even at 10A it only needs to dissipate less than 1/2W and
they'll be more than happy to turn on and off millions of times in complete silence.

https://www.infineon.com/dgdl/sg-auto40v.pdf?fileId=5546d462533600a4015356a094a52ca6[/URL

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Take a look at these MOSFETs.
They're for automotive applications, cheap and handle more power than what the heat pad needs.

Cooling them shouldn't be an issue, even at 10A it only needs to dissipate less than 1/2W and
they'll be more than happy to turn on and off millions of times in complete silence.

https://www.infineon.com/dgdl/sg-auto40v.pdf?fileId=5546d462533600a4015356a094a52ca6

I'll look into that. Thank you!

 

[LA Z]

I just looked up the Hella solid state relays.
I'm almost positive that inside of that relay is a MOSFET similar to the one in the link above.

 

[NoLys1776]

I just looked up the Hella solid state relays.
I'm almost positive that inside of that relay is a MOSFET similar to the one in the link above.

I wouldn't doubt it. I took a bit of a look and what I saw was 3 pin chips and what I could determine is that they are ground triggered. The output of the seats is a single power wire and I don't think I have the brain power to figure a way to trigger them. I could be wrong; I only have a basic grasp of MOSFETs but I can't determine a way to integrate it and can barely decipher the nomenclature. I appreciate it but unless you can direct me to "use this and wire it like this" I think I'm going to just have to go with what I know. I'm also holding out a secret hope that an SSR will switch fast enough that maybe the mechanical relay was part of the reason my original attempt didn't work and I'll be able to use the HELLA one instead with maybe just putting a resistor inline. We'll see.

 

[LA Z]

Unfortunately you are right, it’s not that simple with these MOSFETs.
It would need a few more parts to make it work with the switch.

I will be working on my seats at some point in the near future, and will make something that
will be able to handle the current for the heating pads. Not sure what switch I‘ll be using yet.
If you can wait for me to make it work, I will be posting it here for you guys to use.

It will be some sort of electronic circuit with a MOSFET.
I’ve been working with electronics for a bit over four decades, so I’m sure I can make this work.

I just remembered a module that I used on a few of my projects should also work for you.
it is a electric fan module that can be controlled by PWM or 0-5 volts. ( potentiometer )
It has 12 different power levels and can handle at least 40 Amps, also only cost about $12-15.

part number: D105-1355A

 

[C10Dave]

Thanks for this thread. It's been very helpful, but I have a question. I have a pair of BMW seats that I installed in my truck and I'm trying to get the seat heaters working. My seats only have the one computer on the drivers seat, and not on the passenger side. So my question is do I need to run a wire from the DS computer to the PS to get the heaters to work?

 

[86aggie]

Nope. The wiring with each seat is different. Treat them independently. If you don't have wiring diagrams that you found on Mud, there are some that will distinguish between the two seats.

 

[C10Dave]

Nope. The wiring with each seat is different. Treat them independently. If you don't have wiring diagrams that you found on Mud, there are some that will distinguish between the two seats.

Thanks. I’ll look around for the diagrams.

 

[jesus888]

The switches have a built in voltage monitor and the seats don't really heat unless the truck is running so the battery doesn't run down. Pretty cool feature. Very happy with this setup!!
I am happy I can finally contribute something worthwhile to this great forum of cruiser knowledge.

So just to make sure I understand, because I’m using the switch that you have in your original post…

The 12v power going to the switch is NOT switched power? How does the seat heaters know to turn off when the car is off?

 

[86aggie]

There is a 'feedback' wire from a thermostat in the seat, that tells the switch to cut power, or to turn it back on, if switch is still in on position, when seat cools off. I'm sure someone can provide a more technical explanation than I.

 

[jesus888]

There is a 'feedback' wire from a thermostat in the seat, that tells the switch to cut power, or to turn it back on, if switch is still in on position, when seat cools off. I'm sure someone can provide a more technical explanation than I.

Yes, I believe that is the NTC wire. But I believe that just tells the heaters to turn on until the desired temp is reached...

I am talking more about the entire system being ON, if the vehicle is turned off, but no one turned off the seat heater... since the power wire for the seat heater is essentially constant fused 12v power.

 

[86aggie]

That's up to you and how you run the wiring to the switch - constant or ignition switched power, unless I am still not understanding your question.

 

[jesus888]

That's up to you and how you run the wiring to the switch - constant or ignition switched power, unless I am still not understanding your question.

The power for the seats moving and the seat heaters are coming from this fused distribution block which is powered directly from the battery. So it’s constant power and not ignition switches power. That makes sense because I want to be able to move the seats even if the car is off.

My question is about the power to the seat heaters… if it comes from this distribution block, it will also be constant power, so I’m afraid if I turn on the seat heaters while I’m driving and forget to turn them off when I turn the car off… won’t the seat heater continue running? Therefore do I need to get my seat heater power from switched ignition power to mitigate this risk?

 

[gt7058a]

You could use a relay with an ignition source for the seat heaters so they don’t stay on when the truck is off.

 

[red66toy]

Hey @jesus888 ,
I indeed (just like @gt7058a stated) have them wired to a relay that is only activated if I have the ignition switch on. I didn't want the seats to be able to be heated if the truck was off and the key was not in the on position. I always worry about draining the battery.

 

[jesus888]

I think I may use the stereo remote wire and a relay since the remote wire will be very close to the actual seat heater switches…

 

[red66toy]

Loving these seats tonight

 

[jesus888]

I'm getting CLOSE(r)...