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Old 11-17-2016, 11:56 PM   #28 (permalink)
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Originally Posted by Daox View Post
The arduino will be powered with 12V switched power from the car. Most versions of the arduino have a power regulator circuit built into them, so it can easily accept 12V input. No filters (capacitors) needed as they're built into the regulator circuit.

Quite true, it would not be too hard to program the servo to open incrementally. However, I don't see much advantage? As I see it, ideal operation is to wait until just before the electric fan turns on, then open the grill block. This ensures the radiator is completely full of the hottest coolant possible. That means our bang for the buck of airflow will be the greatest. I'll drop the coolant temp down to just above where the thermostat closes, and then close the grill again. It will cycle open and closed. I don't think it'll be too often, but testing will tell. If it is actuating too often, adding variable grill block logic would probably be advantageous. If anyone sees flaws in my logic, do tell!
A few gotchas for you to watch out for:

The arduino reg generates a lot of heat and may not like extended periods at 14V. Might be better to have a pre-regulator to knock it down to 8-9V and kill more noise too.

By using proportional control of the servo you will prevent cycling and excessive open/close cycles. I would choose an opening amount based on the rate of rise of the coolant temperature and modify this in a closed loop to get equilibrium rather than flopping around like a dying fish between extremes.

You might also consider the cooling fan as an additional input to adjust the strategy - if the fan is running for longer than x minutes then open up more and conversely if it is off for y minutes then close it up a bit.

Ambient temperature should also be used to modulate the opening rate / amount - I would not slam it open if the air temp is -20.

You could also use an analog input connected to a variable resistor to change the reactivity (gain) of the loop for tuning.

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Daox (11-18-2016), Xist (11-18-2016)