I am not asking, I am about to find out.
I think this will be the most dangerous most insane series of tests to date.
I will take my speedy air compressor with 220 volt 2 horsepower 2 pole motor remove the belt and small pulley off and install the 5 inch fan adaptor pulley I am working on.
I have found that the belt driven fans on vehicles are usually slightly over driven. On my 3/4 ton suburban the fan and coolant pump are over driven by 25% of crank speed. At a not completely unreasonable crank speed of about 2700RPMs the fan would be spinning at the speed I want to test at, 3400RPM.
Instrumentation I have is:
A 220 volt kill-a-watt meter knock off. I have had it for a few years but have not tired it out yet. It should display true power, apparent power, give power factor in addition to volts and amps.
My 5kw 220v varrac.
Returning from my
power steering power consumption tests; the optical tachometer.
The new addition, the flir.
I think I am going to test it something like this:
Just put the air compressor on the trailer and cargo strap it down, then just put the fan on the motor and go for it.
The 2 main tests I am concerned with are the fan "free wheeling" and a test with the viscous clutch locked up.
To test the fan free wheeling I would want to warm it up some but not enough to engage the clutch. As it would be while driving along.
Then engage the clutch. To engage the fan clutch just attach my heat gun to a stick aimed at the bi-metal strip and turn it on.
Test it for watts and RPMs with my optical tachometer on a long stick.
I am expecting the motor speed to drop down to 3400 to 3500 RPM.
I expect the motor to draw a lot of power, it will be plugged into my welder circuit that is on a 60 amp breaker.
Then take those RPM readings and use the varrac on the motor with no load and try to cut voltage down low enough to allow the motor magnetic field to slip at that same RPM to get a base line. I could almost just not do this test because I tested the motor when I got it and at no load its very efficient only drawing about 200 watts. I am expecting the motor with the fan attached to draw more like 20 to 30 amps.
I searched around and only found wildly differing numbers.
What looked like the most well documented numbers were provided by some one trying to sell you their fan, so they cant be trusted.
Or the numbers were obtained from "race engines" using solid flex fans, with no or few other details. Was the engine losing 10 horsepower to the fan at 9,900RPM or 6,000RPM, no one seems to know.
No one seems to have provided results of an economy test, with the fan free wheeling at highway speed.
Which is you know, only the most useful scenario by far to have data on.
Based on the first time I replaced a belt fan with electric fans my diesels fuel mileage went up 2mpg.
I believe it takes up to 40 horsepower to propel a suburban along at highway speed. If all of a sudden I am using 10% less fuel after I lose the belt driven fan, the engine is doing that much less work. So just free wheeling that large fan could be using up to 3 or 4 horsepower.
3 to 4 horsepower the whole time while you are driving from point A to B is huge.