Who wants to talk about the Pulse Width Modulation (PWM) of electric fans to only deliver the required power to the fans relative to the load on the cooling system?
Anyone Feel Like Running a Mechanical Fan?
- Thread starter motorheadmike
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How would the factory mechanical fan be any different?
Maybe GM should have done some of this "research" too before selling cars in Canada?
The new Powerwheels Mustang has a variable throttle pedal and PWM controller that is good to over 30 amps. When I see one of these on a curb in 2 years because the $100 battery died again, I'm throwing it in my trunk.
Wow, this has become a 'hot' thread and actually has become quite educational. It's really 'cool' to get schooled on automotive cooling systems with the pro's and con's discussion of each design.
To all the thread participants - thank you for the lively discussion.
To all the thread participants - thank you for the lively discussion.
Personally I think its funny the video didn't do a test of an electric fan setup hp drag. Instead, they just kept sporting numbers they read or heard. With a mechanical fan, you have energy go from chemical, to mechanical, to kinetic energy. With electric fans, you go from chemical, to mechanical, to electric, back to mechanical, and then to kinetic. Every time you convert energy to another form, some of it is lost in each conversion, and electric fans have extra conversion steps.
Something that has not been mention about clutch fans is that they not only freewheel based on temperature, but speed as well. At high speed to WOT, there is not enough force coupling the impeller to the disc and the fan freewheels.
For how much power electric fans pull, they pull surges of 35 and more amps, besides the already mentioned inefficient energy conversions. Let us apply a little math to the often stated 17 hp savings claim with electric fans. One hp = 745.69 watts x 17 hp = 12,676.89 watts ÷ 12 volts = 1056 amps. Clearly electric fans don't draw that many amps from the alternator.
Assuming a very generous 70% efficiency rate for both the alternator and fan motor, (in real life they would not be that efficient, especially older parts from a junkyard). If an electric fan even saves 1 hp from the crank when operating, it would have to pull almost 100 amps, again this cannot be the case with cars having 90 amp alternators.
Many modern cars and trucks use electric fans because they take up less room. Not mention Fwd cars do not lend themselves to mechanical fans as we all know the vast majority of cars are now Fwd. However, large utility trucks, dump trucks, semis, buses, as well as tractors still use mechanical fans. Also if one dislikes old style technology, then why bother with 60 year old engine designs or 30 year old cars? Both are horribly outdated if that is your overriding concern.
Something that has not been mention about clutch fans is that they not only freewheel based on temperature, but speed as well. At high speed to WOT, there is not enough force coupling the impeller to the disc and the fan freewheels.
For how much power electric fans pull, they pull surges of 35 and more amps, besides the already mentioned inefficient energy conversions. Let us apply a little math to the often stated 17 hp savings claim with electric fans. One hp = 745.69 watts x 17 hp = 12,676.89 watts ÷ 12 volts = 1056 amps. Clearly electric fans don't draw that many amps from the alternator.
Assuming a very generous 70% efficiency rate for both the alternator and fan motor, (in real life they would not be that efficient, especially older parts from a junkyard). If an electric fan even saves 1 hp from the crank when operating, it would have to pull almost 100 amps, again this cannot be the case with cars having 90 amp alternators.
Many modern cars and trucks use electric fans because they take up less room. Not mention Fwd cars do not lend themselves to mechanical fans as we all know the vast majority of cars are now Fwd. However, large utility trucks, dump trucks, semis, buses, as well as tractors still use mechanical fans. Also if one dislikes old style technology, then why bother with 60 year old engine designs or 30 year old cars? Both are horribly outdated if that is your overriding concern.
Except... that never happens, at least not in a classic small block V8 engine. My big block Chevy circulates its coolant just like the small block, in the approximate manner shown in this diagram:
When "ice cold" coolant hits the engine, the thermostat is the last thing the coolant touches. Before it gets there, it has already had to flow through the block, up into the heads, then back to the crossover in the front of the intake manifold, and finally into the thermostat housing. By this time, the coolant will have picked up a bit of heat... though it may still provide a brief but sharp temperature drop, which you can see on a water temp gauge if the sensor is located near the thermostat. But that little spike is nothing the thermostat cannot handle--because, yes, the thermostat will close again if the coolant temp goes significantly below its operating temperature--and things quickly smooth out.
Hey, hey! This thread is no place for mind-blowing fancy concepts like that. 😉
I didn't quote the rest of the math because it seemed like just a bunch of incoherent, possibly drunk? rambling.
The video didn't mention the horsepower draw of an electric fan because it is nearly nothing and is a dead horse that has been beaten many times. it takes only about 1/2 HP to run a 30 Amp Fan. See Post #15. Page 50 of the PDF. from 2000. (its 2017).
30 Amps @ 12 volts is 360 watts which is .5 HP even assuming 25% efficiency in the conversion (its at least twice this), it takes a maximum of 2 HP to run a 30 Amp fan. A 300M dual fan will run continuous at less than 25 amps and even on start up will be less than 30 amps.
$35 at the Picknpull. Another $5 for a 2 year warranty.
Looks like it's time to run a mechanical fan on an LS in a G-body.
I like the reliability. If the clutch goes bad and is loose, or if it locks up, it still cools.
The fans that go flat at 140 mph are a joke. The clutch locked up at 4000 is defective. Staggered OEM blades don't create an air wall. There's enough posturing in this thread. A cooling system should be reliable, capable, and IMHO require less maintenance.
I like the reliability. If the clutch goes bad and is loose, or if it locks up, it still cools.
The fans that go flat at 140 mph are a joke. The clutch locked up at 4000 is defective. Staggered OEM blades don't create an air wall. There's enough posturing in this thread. A cooling system should be reliable, capable, and IMHO require less maintenance.
In defense of electric fan reliability I have never had one fail during my 42 years of front wheel drive vehicles. On the other hand I have replaced two fan clutches.
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