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Heated seat thermistor

Posted: 11 Dec 2020, 16:03
by ZsZ
Hi all!

I am in a project, but stuck at the moment. I want to control cheap chinese heated seat pads with the factory wiring and "relay".
In the factory heated pads there is a thermal sensor and the controller senses resistance to ground through that.
On the german forums I was told that this termistor in the circuit is a PTC one that has 2k Ohm resistance at 10C and 15k Ohm at 42C.

My problem is that i am not as familiar with electronic components and I am struggling to find any info how to choose PTC thermistors.
I have found charts and calculators for NTCs but not for PTCs.

I have drawn a graph that says a linear PTC should have ~7.5Kohm at 25C and a ~433 Ohm/C coefficient, but on data sheets of PTC thermistors I have not found any coefficient like this.

Could anybody guide me to the right direction?

Re: Heated seat thermistor

Posted: 11 Dec 2020, 19:16
by Oldiebut goodie
On the Samba they say that it a NTC thermistor! ( Canadian Syncro ) Googling it seems that T4s and Passats are NTC also as are a lot of other vehicles.May well be worth double checking your source. Usually they are rated for resistance at 25 degrees rather than 10, PTC and NTC.

Re: Heated seat thermistor

Posted: 11 Dec 2020, 20:10
by ZsZ
Thanks Oldie,

I have not found info on Samba, but I will search harder.

I have found these numbers also on T4 wiki.
NTC would be good news as I found a few that mathces.

Here is the german forums english section I have asked:

And this is the T4 wiki page:

E D I T:
I found these topics on Samba. They say it is NTC but say no values: ... 929--.html ... order=desc

E D I T 2:
I have found this topic: ... 816/page-4
It looks like it is NTC indeed and the T4wiki is bad - or just noted in reverse and the thermistors I found before are the correct ones

In the German topic I wrote this:
It looks like
SR PASSIVES MF11-682J-B4250 ... 82j-b4250/ and
TDK/EPCOS B57164K0682 ... 00610.html
are the closest thermistors to those values