The debate of electric vs mechanical engine fans

[tekdeus]

I asked my friend who is an electronics teacher what he had to say about electric fans vs mechanical, since many debate that no power is gained due to the extra load the fans place on the alternator. He replied:

"In my (never humble) opinion at mid to higher RPM's electric is more efficient than mechanical for automotive engines also at low RPM's electric can do more work than mechanical for automotive engines

Other advantages
- less inertia with electrical thus the engine can rev up and down more quickly
- less parasitic load because electrical only draws what it needs to accomplish the work at the time the work is needed, whereas mechanical may draw a larger load on a more constant basis regardless of actual demand
- electrical can supply all the needed work at low RPM's however if RPM's are too low for mechanical, it may not be able to accomplish the needed work

I will say however that some of the above advantages may be more academic then actual, because there are other overriding conditions that moderate the differences such as cost, reliability, weight, drive-train inertia, actual work needed, etc. Also some of the above advantages are application specific, thus a generalization would not be an easy claim to support!"

I think he may have some good points IF there only was a better designed fan control module availabe. I have dual fans and can only find controllers that will turn them on or off at a set temperature. If I had a single fan, they make dual speed controllers with a low and high speed setting which makes more sense, espesically in winter, when the low speed would probably be sufficient most of the time. Ideally, a controller should control both of my fans and have a variable speed to maintain the set temp, but no such thing exists that I can find. Any idea why? I think they use PWM’s to controller the speed, does this limit the variable speed possibility? Currently, my fans will remain off until the set temp is reached, then they stay on all the time.

I'm interested to hear your opinions on this, and to see if anyone at least knows where I can get a dual-fan, dual-speed controller?

 

[Fozbo]

Ideally, a controller should control both of my fans and have a variable speed to maintain the set temp, but no such thing exists that I can find. Any idea why?

This is the job of the coolant thermostat (maintain the set temp that is). Why would you want two things competing to do the same function? When you get up to temperature, the fans would bump down, the engine heats up, the fans would bump back up as the thermostat was opening, the engine would cool off too much and so on and so forth. In short it seems like you would be fighting yourself. There would have to be some sort of delay wired in on only the kick-off of the fans such that they would only kick down if the engine was definitely cool enough, but kick on the instant it heats up too much (kinda like a fail safe). This could also be accomplished by setting two temperatures defining a range, the lower one would kick the fans off (only if they were on) and the upper one would kick the fans on (only if they were off). Meaning that in the middle of the range, the fans would keep doing what they were previously doing until they hit the end of the range.

The thermostat actually does this very well in a very simple mechanical way (increases or decreases in temperature expand or contract the spring that operates a valve allowing coolant to flow to the radiator). Why over-complicate the process with more wiring? The upside is that the variable speed control would save you a little bit of load on the engine, but overall I don't think it would be noticeable in either power or efficiency. That and I don't think that changing the speed around versus keeping them going will hinder the life of the fan motors all that much seeing how long some stock fans on other cars have gone.

In any case, if you can get a controller for one fan, then it can at least be done by picking up a second controller for the other or modifying the single controller.

You could also look at making a controller yourself using some relays and resistors to modulate the voltage (actually very similar to how the stock fuel system works by modulating voltage to the fuel pump).

Just some food for thought.

Edit: Just thought of something else. If a two speed (low and high) is what you're after with a dual fan setup, why not just have one fan on a switch and leave the other on all the time? In effect it gives you a higher and lower flow (and less draw on the alternator). I'm no electronics expert, but I am pretty sure you can accomplish this by utilizing the stock temperature probes. Once you have the range that it outputs, you could hook it up to a relay that closes at a certain voltage and pulls in the power to run the second fan. Also, since the fans are running at their optimal efficiency (according to your teacher above, higher being better than being very slow due to heat) and just dropping one out every now and then, then the system would be more efficient than if you were to modulate the speed of both. Anyway, it is late and I think I'm just rambling at this point.

 

[supraguy@aol]

The T-stat would not be competing against the fan, as the T-stat's job is not to cool the engine- It's job is to permit or prevent flow to the rad. The fan's job is to cool the engine. I used to have twin FAL's installed in my car, and they worked fine until the fan controller crapped out. Then I set up double relays, both wired into a 215* temp switch, located in the Tstat water elbow. The switch would shut the fans off at around 205*. I don't know why your fans continously stay on once started, Tek. Mine worked flawlessy this way, except that after shutdown, the water elbow would get so much latent or radiated heat, that the fan would keep running for at least 10 minutes. Since there was no coolant movement, the only thing that would cool down was the water IN the radiator, and not in the block. This required that I shut down, go get a snickers, come back out, and run the car for about 30 seconds. My plan was to move the temp switch to the side or bottom of my radiator, so that the fans wouldn't have this run-on problem. I even bought an aluminum bung to weld on, but later decided that I'd rather just go back to a stock mechanical fan. I haven't noticed any loss of performance, and of course, no change in cooling/ temps.
I think that people that have problems with overheating-and decide to go with electricals- are sometimes simply just missing the stock fan shroud, or have a blocked up radiator. I think that if I had to name the weakest link in our cooling system, it would be the size of our stock radiators. That's where I would make the first change in the system, not the fans.

Oh- to answer your question- I thought that HKS made a pretty sophisticated fan controller.

PS- if anyone wants some FAL's, just hit me up.
:biglaugh:

 

[black89t]

the only reason i would ever use electric fans would be because of space. THATS IT. that is the only area where the electric fans are more beneficial. other than that when comparing the two as far as performance, reliability, and simplicity there is no comparison. i feel its as simple as that.

 

[figgie]

the answer is quite clear.

Let's look at ANY setup that has constant loads on their engine with a cooler burning fuel. 100% mechanical 100% of the time.

There is no debate, electric = 2nd place.

/thread

 

[bmoss85]

electric fans seem to work fine for plenty of cars, but i would only replace the mechanical fan for an electric one that would flow more.

 

[becauseican]

Brad, After your drive to Vegas/ Nevada last fall you should already have your answer.... your car got hot on every incline........one of the problems with your setup was that the fans were continuaously on, this is hard on the fans and wears them out prematurley. I ran electrics for a few years, and everytime there was a long hill the temps would climb. I had a custom HD realy seteup with 12 gauge wires for each fan and a B-Cool sensor in the water neck with a 180 on 175 off fixed setting, this was the best I could get out of the FAL 210's and it still got hot in the summer, never mind with A/C on. Now with my mechanical fan I havent seen a problem, even with the 100+ MPH cruising speed on the way to Vegas through the desert with A/C blowing max cold.

For the 1-2 HP you might gain from electrics, I would say its not worth it, esspecially at 400+ hp. Mech fans are super reliable and will move more air than any electric that can fit in the mk3 engine bay. The shroud is one of the main things that can cause a hot running engine, dont run without it.

There is no need to try to re-invent the wheel, when a perfectly round one already exists!!

 

[figgie]

Randy, correct!

The issue is the 210 are crap. The good fans cost money, and the reputation of mkiii owners being cheap did not self combust into this reality out of no where.

Hell FAL even updated that 210 with a new bigger, higher flowing, higher current pulling fans now.

Mechanical is the only choice unless you are torquong the motor over so much to chew the fan shroud up.

On that note. Thread is done. There is no debate, only beliefs.