How much power does a belt driven fan use

[jamesqf]

Another question is how much energy it takes to drive the belt (plus any friction in the clutch &c) when the fan's not turning.

Seems like you could get a pretty good ballpark estimate of fan power requirements from an ordinary household fan of the same diameter.

[oil pan 4]

Originally Posted by jamesqf

Another question is how much energy it takes to drive the belt (plus any friction in the clutch &c) when the fan's not turning.

Seems like you could get a pretty good ballpark estimate of fan power requirements from an ordinary household fan of the same diameter.

The belt is between 98% and 99% efficient.

The fan does not stop when the clutch is disengaged. The viscous clutch always spins the fan at 20% to 50% of pulley speed.

The blades of a household fan use a much shallower angle of attack.

[user removed]

Viscous clutch fans on start up run runabout 3k rpm. When you hear them get quiet, the thermostatic valve is allowing more slippage and the fan speed drops down to 1500 rpm until things heat up. Then it closes the slippage valve and the fan speed increases. When aero was not a concern the airflow past the radiator would probably drive the fan at 1500 rpm at 70 mph, even if it was just a free wheeling fan, so the losses would be much lower.
The bimetallic spring in the front of the clutch senses the temp of the air flowing through the radiator. It's a very reliable system. When the clutch is shot, I used to grab the fan, WITH THE ENGINE RUNNING, and spin it backwards to show the customer it was defective!

regards
mech

[windy]

One factor is the weight of the fan fan/clutch assembly.
The jeep wagoneer / grand wagoneer with the 360 v8 from the 70's have a very heavy combo of about 6 lbs (2.7kg) for the 19" fan diameter and 7 blades. I replaced mine with from an early 80's mercedes 560 sl which is 18" diameter but has 9 blades and weights 4lbs (1.7kg) because the fan is alumimum not steel, and has some fancier curve on the trailing end of the blades. Both fan clutch have alsmost the same weight 2lbs 10oz and 2lbs 3oz.
I tried to calcutate the linear and angular velocity to determine loss of HP, which of courses does not account for the fan clutch activation, but both fan combos have the clutch, so the limiting factor could be assumed to be the weight, albeit the jeep fan is steel all around and larger, and the mercedes is a lot lighter on the perimeter so the momentums are different.

the link is algebralab.org/lessons/lesson.aspx?file=Trigonometry_TrigAngLinVelocity.x ml

So between 4 and 7 hp was the result, which does not take into account that at some point the clutch partially disengages the fan.

Indeed a tach could be used to determine the speed of the fan under different temperature conditions, but I have not tried to find out yet -this v8 is not a commuter-

A few people have tried to go electric but those vehicles when used for what was their original purpose, which is slow speed on rough trails, will invariably run to the limit of overheating, albeit the taurus or contour dual speed fans seems to be successfulll but need to have a larger alternator -creating more drag- and some rewiring.

cannot post links yet, I have been a lurker for too long

[windy]

Originally Posted by Old Mechanic

When the clutch is shot, I used to grab the fan, WITH THE ENGINE RUNNING, and spin it backwards to show the customer it was defective!

Very good point, but a much safer way for the commoner, is to have an assistant turn off the igntion while you watch the fan, with a warm engine, the fan should stop spinning within one second, when bad it can spin for over 2 seconds...

[oil pan 4]

I am having a bit of a problem getting the pulley off the motor.
Plus I need to use my air compressor. Now I did manage to remove the old pulley about 2 years ago when I rebuilt this compressor. I replaced the original 2 inch diameter pulley with a 2.25 inch one to get more air out of the compressor.

I am thinking I might just buy the largest 220 volt powered 2 pole 5/8 inch shaft motor I can find, which is a 3.5 horsepower motor and put it on a skid. A 3.5 horse motor should be able to run at 7 horsepower for extended time and be able to run 10 horsepower briefly.
I already have a box of belt drive stuff with 5, 6 and 6.5 inch keyed 5/8 inch shaft pulleys.
Then I could test anything I can stick a V-belt pulley on, underdrive or overdrive it as needed.

[windy]

Originally Posted by oil pan 4

I am having a bit of a problem getting the pulley off the motor.

Rust? pb blaster or 50/50 acetone/transmission fluid works as well.

Otherwise a little heat... but watch for plastic or rubber parts