I have built the test circuit and get a good PWM range response in both +12VDC to +15VDC with a simulated load. NOTE: the fan will run at the same speeds with the engine running and not as the PWM percentages of voltage vs. duty cycle output to the fan are proportional to the voltage increase. The control voltage does NOT change with the engine running or not. It remains constant depending upon the selector position. Full off is 0VDC and full on is ~+7VDC.
Example: At +15VDC, the PWM Duty Cycle output of ~75% at +12VDC will output ~98% PWM Duty Cycle at ~+10VDC. This means that regardless of the voltage supplied to the fan controller, the PWM duty cycle should never exceed 100% and total power to the fan will also never exceed 100% of +12VDC.
This is my proposed circuit. All components, including board manufacture can be sourced for less than $12 per board in batches larger than 100. This excludes the "custom" fan control socket for connecting to the existing wiring harness plug. I have yet to find the type of plug with the proper pins to make it work. The other option is to source the pins by themselves and just solder them to the board with the appropriate spacing. All of this cost does NOT include assembly.
A small "Test" batch of 10 to 20 boards would spread out the setup cost, which is usually about $100. So we are looking at prototypes complete for about $30 to $40 in this small of a batch. If there is enough of a response, I would be willing to build the first "Test" batch and ship them.
I still have to build the first prototype to test the thermal requirements of the MOSFET heat dissipation and verify the heat sink will be necessary and cost effective. This is also pending the connector and/or pins for the factory plug.
On the BMW side of the isle, they have the same issue, but it would require a different plug to connect to their harness.
Like anuses, everyone has an opinion. Let's hear yours.
