hi, sorry , i suppose i should have said, i just need a potentiometer to
control the speed , it doesnt need to be controlled by cabin heat
etc...., the fan controller in my car isnt working and they havea tendency
to fail , so i am trying to construct a bit more robust one . everything
is working fine the heat , aircon , its just that the factory controller
is broken and the fan always stays on really low,.
thanks,
mark k
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Sorry, I don't have a schematic for you, just a couple of ideas and
pointers. 25 amps is NOT overkill by any means as most heater blowers
will pull that much easily. So I would not use your 30 amp darlington
and would only feel good about your 50 IF it had a real good heat sink
arrangement.
Most auto heater blowers use wind cooled wire wound resistors in
series with the blower motor circuit to attain low and medium speeds
with high speed being a direct connection to 12+ volts. Some
regulatory body specifies that a super low speed is mandated to be on
all the time to guard against carbon monoxide poisoning, which is
probably the low speed you've noticed.
What typically happens is the connection between the standard copper
based slip on connectors corrodes with the ni-chrome wire of the wire
wound resistors in the fan speed circuits. Silver soldering the
connections maybe an easier solution?
If I were to build a circuit for your application I would use UA78s40
switching IC to drive the darlington that would drive a torroid step
down/step up circuit. Switching in different resistors in the
voltage feedback circuit would then select fan speeds. And in my old
Subaru for example, I also need to hit the fan motor with some 16-17
volts in order to have me a super high speed for those really cold
winter days.
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