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Old 03-08-2021, 10:21 PM   #1 (permalink)
EcoCivic
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Radiator fan power draw on highway?

Hello everyone, I am wondering if anyone has tested to see how much power electric radiator fans draw while driving down the highway compared to while stopped.

The reason I am asking this is because a lot of cars (mine included) unnecessarily run the radiator fans whenever the AC compressor is running, even at higher speeds where there is plenty of natural airflow to cool the radiator and condenser without the help of the fans. This potentially wastes a significant amount of power and runs the battery down faster than necessary for those of us who disable our alternators.

As an example, my car has dual electric radiator fans that draw around 23 amps while on. 23A X 14V = 322 watts. Assuming a standard alternator is 50% efficient, that's a draw of ~644W from the engine, which is equal to about 7/8 of a horsepower. Assuming the AC compressor runs at a 50% duty cycle on the highway (which is often pretty close to accurate on my car depending on weather and fan speed), that averages out to a constant load on the engine of about 3/8 of a horsepower. Although not crazy high, that's definitely high enough to be worth figuring out a way to eliminate. People do much crazier things for much less gains!

I have a few ideas of how to automatically disable the fans at high speeds, but I would like to know what the power draw is at higher speeds before implementing such a system because I suspect that the draw may be less while driving at high speeds since the air being forced through the fans would theoretically reduce the load on the motor by helping turn it like a windmill, but I am not sure how much the draw would actually change.

I am going to be testing the power draw at different speeds when I have time and will report back, but for now I am wondering if anyone else has thought about this or done any testing.

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