E39 heated rear seats retrofit project.

Winter is coming.

The plan is to fit seat heating pads to rear bench and backrest and add 3 stage switch, similar to the one for front seats, to control it.

So far i have found only 2 similar projects from the net. One was with e38 dial type switches and second had 2 stage switches from x5.

My plan is to butcher one switch centre and try to combine it with rear cup holder or cubbyhole.

I have ordered 2 sets of pads. When they arrive, i will measure the power they draw and temperatures and go from there.
It could be a very slow project, so bear with me.

Examples from net.
http://images52.fotki.com/v637/photo...IMG1397-vi.jpg
http://farm3.static.flickr.com/2446/...348aa68530.jpg

PS. No one ever sits in the rear of my car :cool:

Fairplay to you. Great project to undertake, looking forward to your slow updates.

Very nice love this car and it just keeps getting better

Another option for you is this
http://img.tapatalk.com/d/14/09/30/a8ehemu8.jpg

Theres also another with an aux port in the middle

Quote:

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Originally Posted by Gar

Very nice love this car and it just keeps getting better

Another option for you is this
http://img.tapatalk.com/d/14/09/30/a8ehemu8.jpg

Theres also another with an aux port in the middle

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I like this one. I may go the x5 button route afterall.

One of the lads in work has it on his E60 along with a heated steering wheel, very cool (heated :D) option

Heating pads arrived today. I measured resistance and came up with three power settings.

Stage 1:
U=12v
R=11.3 ohm
I=1.06A
P=17.7W

Wiring diagram for stage 1
https://lh5.googleusercontent.com/-_.../stage%2B1.jpg


Stage 2:
U=12v
R=7 ohm
I=1.7A
P=20W

Wiring diagram for stage 2. Resistor 4 ohm, minimum 25w, 40w recommended.
https://lh5.googleusercontent.com/-0.../stage%2B2.jpg

Stage 3:
U=12v
R=3 ohm
I=4A
P=48W

Wiring diagram for stage 3.
https://lh6.googleusercontent.com/-C.../stage%2B3.jpg

Sorry for my bad MS Paint skills :D

Put all 3 stages to test today. Stage 1 & 3 are good. Stage 2 is no go. Resistor gets too hot for my liking. So back to drawing board with stage 2.

Great project ! How are you going to wire it ? ie how is the link used in stage 3 not going to effect stage 1.
The easiest way I see it involves lots of relays I'm curious about how your going to do it .
About the 3 stage switch if you have it on its highest/hottest setting are the other 2 (low & medium) contacts made ?

Edit: I see you don't have the switches yet

I will use relays to switch between stages, so that when stage 3 is in effect, stage 1 and 2 are disconnected from the pads. Plan is to use arduino to control the relays.

New idea for stage 2.

Values or r2 and r3 will define current. I use potentiometer in place of r1 and r2 to get the desired temperature and replace it later with correct resistors.
https://lh5.googleusercontent.com/-z...Bregulator.jpg

I hope this works. :D

I love it.. :D

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

Its a tasty e39 i was tailing it up the mountains a few months back very very nice car [emoji41] thats the only time iv ever seen it very mysterious e39 [emoji1]

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

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.

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.
https://lh6.googleusercontent.com/-J...28Small%29.jpg

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.
https://lh3.googleusercontent.com/-m...28Small%29.JPG

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.

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

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
https://lh3.googleusercontent.com/-7...28Small%29.jpg

Switches.
https://lh3.googleusercontent.com/-_...28Small%29.jpg