E39 heated rear seats retrofit project.

[mcung13]

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.



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

[Johnnyghia]

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

[Gar]

Very nice love this car and it just keeps getting better

Another option for you is this


Theres also another with an aux port in the middle

[mcung13]

Very nice love this car and it just keeps getting better

Another option for you is this


Theres also another with an aux port in the middle

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

[HealyC]

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

[mcung13]

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



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

Wiring diagram for stage 2. Resistor 4 ohm, minimum 25w, 40w recommended.


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

Wiring diagram for stage 3.


Sorry for my bad MS Paint skills

[mcung13]

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.

[KevinF]

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

[mcung13]

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.

[mcung13]

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.


I hope this works.