E39 heated rear seats retrofit project.

[RossYB]

I love it..

Can we get a project thread with a few pics of your E39?

[Gar]

Its a tasty e39 i was tailing it up the mountains a few months back very very nice car thats the only time iv ever seen it very mysterious e39

[mcung13]

Thanks guys. One problem with living in the sticks is that you can't attend most of the meets.
I will try to find some time and start project thread in the cars section.

[mcung13]

Small update then. Tip33 transistor in stage 2 gets too hot. I would need to use large heatsink to keep it cool. I will substitute it with more robust and powerful 2n3055 and see how hot that gets with small heatsink.

[mcung13]

I have been busy lately and it is hard to find time for projects. But i had a chance to look at this project last weekend.

I did use 2n3055 instead of tip33. But the temperatures still remained too high. I had to use large heatsink to keep the transitor temperature down.
Size of the heatsink.


I looked into e39 front heating setup. It is quite sophisticated setup.
Heating pads run at full 10A current until desired temperature is reached and then the current is pulsating between 0A and 10A to keep the temperature.
Temperature is measured with 10kohm ntc thermistor in the seat base heating element.

I also looked at e38 setup. Instead of limiting current, it limits voltage instead. Same 10kohm thermistor is used to measure temperature and as desired temperature is reached, voltage is reduced to keep the temp.

So I have decided to scrap the idea of creating my own switches and ordered some e53 heating switches.
Like these.


Also i found, that the ebay seat heating pads are very weak. They go hardly over 35 degrees.
There was this guy in German ebay, who was selling genuine e87 heating pads. I can't find the link at the moment, but looks like this is the way to go.

[CTRob]

Heated rear seats are deadly. Have them in the e60 and the folks love them :-)

[mcung13]

Got a set of early e65 rear seat heating pads and x5 switches.
Up to 2003, e65 used same type of seat heating pads as e38.
10k thermistor in base and single heating element per pad. Form 2003 new types of pads were used with dual heating elements in each pad.
So if anyone plans to use e65 ones, make sure to use pre 2003 pads.

Heating pads


Switches.