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Thread: E39 heated rear seats retrofit project.

  1. #1

    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.



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

  2. #2
    BMWHaus Contributor
    Join Date
    Aug 2013
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    399

    RE: E39 heated rear seats retrofit project.

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

  3. #3
    Moderator
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    8,000

    Re: E39 heated rear seats retrofit project.

    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

  4. #4

    RE: E39 heated rear seats retrofit project.

    Quote Originally Posted by 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
    I like this one. I may go the x5 button route afterall.

  5. #5
    BMWHaus Guru
    Join Date
    Jul 2013
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    1,706

    E39 heated rear seats retrofit project.

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

  6. #6

    RE: E39 heated rear seats retrofit project.

    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

  7. #7

    RE: E39 heated rear seats retrofit project.

    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.

  8. #8
    BMWHaus Contributor
    Join Date
    Jul 2013
    Posts
    470

    RE: E39 heated rear seats retrofit project.

    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

  9. #9

    RE: E39 heated rear seats retrofit project.

    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.

  10. #10

    RE: E39 heated rear seats retrofit project.

    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.

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