Uh oh, your using the PNW quote and reply line by line technique :: :: ::

Seriously, I missed most of the debate but I have seen dyno test after dyno test where the RWHP numbers (the one's we like) have gone nothing but up with electric fan swaps and also with pulley changes and electric water pump installs. Either combined or seperately. That's where I say "heck, sure lookie like it works ta me!" :: ::

 

You should have just let it die, nothing worse than focusing on the trolls on a board.

But maybe this will help you understand the true benefits of an electric fan over stock mechanical:
http://www.network54.com/Hide/Forum/message?forumid=215655&messageid=1066184641

 

Going to play devil's advocate here Jay. On those dyno tests, was the electric fan running at the time? The big advantage of electric over pulley is that it is not a constant draw. Power isn't free.

Slade

 

Yes in both cases... and even if it was not on then you are seeing the advantage of it already since it has the ability to only come on when necessary and turn at a constant RPM instead of varrying with the engine RPM etc.

 

I must add that I like your alternators.....and the aircraft they are attached to.

Yes, ejukachun only seems to work on a few. ::

 

I think the biggest advantage of an electric fan (which I don't have) is that it will probably only run at low speed. Once the car is moving the forced airflow should be sufficient to provide adequate cooling, so at that point parasitic power loss drops to near zero.

I agree however, that using an alternater to generate electricity, converting it to battery storage, and converting it back to active current to run a motor driving an electric fan has to eat up a substantial amount of HP in transition losses. It is just that this loss generally occurs when you aren't asking the engine for a lot of power.

What is the final average loss of the two systems? The fixed fan probably loses more as it does not take a vacation like the electric fan system does.

JMO - not based on facts or observations!

John Harvey

 

Jay; I'll go along a little with your dyno "facts" , now lets get into the real world of driving !
How many hours are these dyno runs ? Surly the A/C-lights-stereo are not operating and the battery has a full charge (i.e. alternator is putting out almost 0 amps).

 

As one of the participants in the original discussion, and an engineer myself, I'd like to just clear up a few things. I think on of the problems with that original discussion was that 66coupeNW was focused on the alternator and I and maybe others were talking in general terms. I would agree that there is little be gained driving the alternator slower. If it needs to produce 40 amps it's going to produce 40 amps, regardless of it's speed (if it is capable, anyway). I also agree that in certain cases there may be side effects to running other accessories slower, mostly in loss of some performance. However, the difference in speed created by changing engine speeds is a much bigger factor in some cases than the size of the pulley. I design A/C drives for vehicles as part of my job, and do a lot of experimentation with changing drive ratios, not to gain HP but to optimize the A/C performance. More times than not it takes a dramatic change in ratio to make a significant change in perfromance.
I've seen underdrive pulleys create HP on a dyno, so I know for a fact that it works. My guess is the gains are probably made mostly in the water pump and fan.
Now, electric fans. One thing everybody is ignoring is that the power that is necessary to turn an electric fan versus a mechanical one. They are different blade designs and run at different speeds. They are not an apples to apples comparison. I fully agree that energy does NOT come from nothing. Theoretically, if you had a mechanical fan and an electrical one that pulled the same amount of air, they would use the exact amount of energy to do so. But an electric fan has more losses due to efficiencies, so it would actually use more power to turn than the mechanical fan. This means that if an electric fan doesn't use more power than a mechanical fan, it isn't pulling as much air either. The advanctage to an electric fan is that it only runs when it needs to.
That's my story and I'm sticking to it. I'm also shutting up now.
Jim

- IF any of this is wrong, it's because I wrote it in about 10 seconds, certainly not because I'm a bad engineer! ::

 

I'll add one note based on my experience in dynamic system modeling. We normally assume the fan power increases as a cubic function of speed. This is a fairly accurate assumption. So if you double the fan speed the power will increase by a facter of 8. A fan that draws 1hp @ 2000 rpm (engine speed) will draw 8hp @ 4000 rpm and 36hp @ 6000 rpm. That is why the mechanical fans look so bad on a dyno run. Electric fans don't speed up with the engine so they provide a considerable advantage at high engine speeds.

 

Youre debating Efficiency vs. HP.. that doesnt work... Yes the direct drive is more efficient use of power for the fan, but the energy losses in the electric fan setup are irrelevent since the fan spins to cool the system, and you get more usable HP where you want it most.. The Rear Wheels....

Correct me if I'm wrong, but an alternator is designed to produce adequate power to keep the system charged under normal operation.. And an alternator does not create more load on the engine when it puts out more current ( its not harder to turn an alternator that needs to put out 5 amps than when the same alternator needs to put out 25 amps). The load on the engine is the same nomater how much power is needed from the alternator, its just a mater of wether the alternator can provide that power at the given speed it is spinning.. So an Electric fan would then require no extra HP from the engine beyond what is normally required, where as a mech fan requires the engine HP directly to function, and the load on the engine is directly related to the load of the fan.. Therefore an electric fan frees up available HP, provided the alternator you have is sufficient to keep the system charged..

Underdrive Pulleys Do free up more HP by gearing the accessories to spin slower, but you need to make sure that the accessories are still producing the requiered power at normal operating speed..

 

Now we're back to the "power is free" theory. If the electric fan doesn't use power, then how does it turn? The power does't come from nowhere, it comes from the engine through the alternator. You may be right about the alternator load not changing, but I don't think so. To say the load on the alternator is constant would be saying that the power is free, and that can't be the case.

 

Jay; I'll go along a little with your dyno "facts" , now lets get into the real world of driving !
How many hours are these dyno runs ? Surly the A/C-lights-stereo are not operating and the battery has a full charge (i.e. alternator is putting out almost 0 amps).

If you're gonna race with the stereo on and the A/C then you're not serious and should just go home ::

 

Is there a reason we all want to argue conjucture when someone, namely me, was nice enough to post a link to an article that DYNO tested several fans on a motor with an alt running and PROVED beyond a doubt that electric fans free up HP versus their mechanical counterparts?

 

You are wrong about the alternator drawing the same power regardless of current. Power equals voltage times current, P = VI. If the alternator is delivering 5 amps at 12 volts it is delivering 60 watts of power. If it delivers 25 amps at 12 volts it is deliver 300 watts of power. The alternator will always draw more power from the drive belt than it will deliver to the electrical ciruit due to inefficiency. The alternator will always draw more power as the current delivered increases assuming the voltage fairly constant.

 

Because from an engineering and physics standpoint it can't happen, if all else is equal. I just scanned the article you linked to, and I don't see any mention of airflow, which means the whole test is virtually meaningless. This article is comparing the power output of the engine USING various fans, but to actually compare the fans, they all need to be pulling the same amount of air, because ultimately it is the air that produces the load.

 

lol

Dude. My car ran cool with a flex fan, my car runs cool with my electric fan. What the heck to I care if they pull exactly the same amount of air? The car runs cool and has more HP.

Using your logic I can't say one car is faster than another in the Quarter mile unless they weight the same.

j/k

Fan effecientcy is an important component but not what we are debating here as I understand it. The point has been asserted that all us folks running electric fans have wasted our money because we get no gains because the HP savings by removing the mechnical fan are soaked up into the alternator when it has to power the additional accesory. They also used a very popular and large flow fan so that the nay sayers can't say "well they used a 4 inch personal fan that wouldn't be capable of cooling the car" they picked a fan anyone who had the motor and wanted to buy an electric can would have picked.

The linked artical shows the HP of the motor with no alt or fan, just and alt, and then the motor with an alternar and various fans to show the draw on current DOES NOT equal the gains from removing the mechanical fan resulting in a loss and no real gains, but instead a marketable increase in usable power from the motor.

 

I'm not even sure what were arguing about anymore. I think most people understand that the electric fan will use less power overall in average everyday use and in high rpm applications such as drag racing. Some people just don't understand physics behind it. I'm done with this thread.

 

GEES I'm sorry, I didn't realize WE were talking about racing, I thought WE were talking about alternators & electric fans! ! :: ::

Local high school science class has an alternator hooked up to an exercise bike , just turning up the volume on the tv or stereo increases the effort to pedal , if you really turn them up the pedals just stop ! ! !

 

You and the article are talking a comparison of a car/engine with one type of fan versus another. We are talking about comparing actual fans, independant of the car. The airflow IS the load, so it is absolutlely necessary in order to compare fans. To use your analogy, doing what the article did was like comparing horsepower-to-weight ratio without considering the weight.
Take an extreme example - two mechanical or electrical fans. One has typical blades that move air. The other has flat blades that move no air. Which do you think will require more power to operate? Still think airflow is unimportant when comparing fans?

 

Jim were arguing over nothing.
The orginal post dealt with "Will I get more HP by going to an electric fan" not will I get more air flow.

 

Whatever. But as with many posts, it evolved into something more than that when we started talking the efficiency of a mech fan vs. an electric, no? I'm trying to explain that the power it takes to run a fan is dependant on the airflow that it produces. Yes, if you want to look at the article and compare the various fans, you can pick one that allows the engine to make the most power. Unfortunately, it is also most likely the fan that is doing the least amount of work. If that still allows the engine to run cool, then great, it was a good choice. But the most fundemental rule of testing is that you have only one variable per test. This article has two (the fan type and the airflow) and ignores one. Based on this article, there is no way to say that under identical conditions (which would include airflow) one of these fans is any better than another.

 

Explain to me the point of putting all the power under the hood unless you intend to use it somehow? If you are after the most power out of your setup for whatever reason then it has been demonstrated time and time again that an electric fan is the way to go. If you are running all those accessories than you are not going after the same thing ... put the money into a better exercise bike ::

Installing a more efficient radiator (aluminum) and higher flow water pump with things like aluminum heads and intakes will lower the requirements of your fan's CFM, therefor a standard fan would be using up power for no reason. Sort of like putting the TV and and cranking the stereo when all you want to do is watch TV :: And does that bike have gears ::

 

Innocent questions...

How does a clutch fan compare to a fixed fan vs an electric fan?

Does a 40A alternator take less hp to run it than a 100A alt?

If a 40A does draw less hp but you have to upgrade to a 100A alternator in order to put in an electric fan do you leally gain anything? Can you put numbers on what the gains are, i.e. 2hp?

 

Okay, I'm gonna say this one more thing and then I'm out. Jay, I agree, but there are two or three different conversations going here. One is whether or not a car will make more power with one type of fan vs. another. Another is regarding the efficiency of the fans themselves. Yet another one is related to the first two in that it questions how an electric fan can be less efficient electrically and still help the engine make more power.
Several posters have gotten these questions confused when providing answers.
Here's the bottom line on fans:

You don't get something for nothing.

An electric fan producing the same airflow as a mechanical fan is less efficient (uses more power to operate).

Electric fans are known to use less power because they only come on when needed whereas a mech fan runs all the time.
There are only two ways I know of for an engine to make more power using an electric fan. One is that the fan is turned off, and the other is that the fan is pulling less air than the fan it is being compared to.

None of this has much to do with the original post about underdrive pulleys, nor this post which started out as a reply to a flame.

 

Don't worry Jim I understand what you are saying