In article ,
Chris Green wrote:
Jim Stewart wrote:
On 07/03/2020 08:46, Rod Speed wrote:
Jim Stewart wrote
I take it car blower resistor packs are cooled by the airflow of the
fan they are controlling....?

Unlikely they use resistor packs anymore.
what is used then ? .....

Electronic control using MOSFETs probably, switch the power to the
motor on and off very fast varying the on/off ratio to give speed
control. There are lots of speed control chips available off the
shelf for driving the MOSFET, overall very cheap to implement nowadays
and can easily be well over 90% efficient as MOSFETs are very nearly
perfect switches.

First car I had with that was a BMW E39. Known as the hedgehog. That also
was cooled by the heater airflow. First thing that failed in that car too.
Oddly, the resistor pack in the 35 year old Rover is still fine, and the
heater motor near always on the mid setting.

The controller on the BMW was very nice. On auto, it started off on low
with the engine cold, then ramped up the speed as it warmed up to heat the
interior as fast as possible, then ramped back down to a quiet setting
once the desired cabin temperature was achieved.

--
*If all the world is a stage, where is the audience sitting?

Dave Plowman London SW
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