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Originally Posted by xenon
Perhaps but what I'm saying is as standard you can set the fans to come on at a certain time so if it was not detrimental to also have the electric heater on then BMW would have given the function as it would be very useful. I suspect though that to get any decent heat the heater will need to be 250W if not more, which would draw 20A. On a cold day that would kill the battery pretty quickly so there is a good reason why BMW deny this functionality. You might be able to code it out but is there any point getting to a defrosted car that won't start?
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Exactly, with a larger draw than you suggest as well. BMW data states the following for the E87 & E9x models.
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The only power that is available to the electric auxiliary heater is the excess power from the alternator. The maximum heat output available is 1250 watts. At maximum heat output, the current draw is limited to 74 amperes (± 10%). The electronic circuitry in the electric auxiliary heater automatically adjusts to the respective minimum. (Request of the IHKA and limitation by the DME.)
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Even in use the auxiliary element can be switched down, if the current available is not enough. It is like many functions including heated rear demister and heated seats, it is in the list for % function and/or clocking if the power available is too low.
So like you, I can't see any way it can be coded without messing with the energy management bigtime.
HighlandPete