There's been some discussion here about the possibility of saving some horsepower by eliminating the engine driven radiator fan, I've been working on a project at work and came across this information.

We purchased a 175 kilowatt diesel electric power generator, it's powered with a 300 HP at about 2,000 RPM Cummins turbo diesel, 504 ci, 8.3L. The radiator cooling fan on it is about half again to twice the size of an automotive cooling fan and it's not clutch driven, it's a plain old fan bolted to a belt-driven pulley.

The Cummins literature states the fan uses 17.7 HP of engine power.

So that's how many horespower it takes to cool a stationary diesel putting out 300 continuous horsepower, 24x7. The fan isn't clutch driven, it's always running full speed and the big diesel doesn't have the benefit of airflow from forward vehicle motion.

My point is that this makes the claims of saving 15, 20 or more HP by going to an electric radiator fan on a motor vehicle seem hard to believe. Our vehicle fans are usually clutch driven, and they're not putting out 300 continuous horsepower with that much of a huge quantity of heat to get rid of.

Unless I'm missing something that makes this comparison invalid...
Anyway, thanks for the soap box!

 

Well you don't get anything for free. The alternator has to provide electrical power to an electric fan. It may be more efficient. My main concerns have been the ability of electrics to cool a big motor (cfm) and running two for back up. Theoretically a thermal/clutch fan is very good but they seem to lock up at the wrong times to me.

Bear Tracks

 

Well, sometimes you do get some things for free. While the altenator will pull some horsepower for the electric fans (fraction of a horsepower, actually) the neat thing is that when you are in your power curve at 2500-5500 rpm, you will probably be moving fast enough not to require having the electric fans on at all...so if the fans are off, there is no draw on the altenator and no hp lost to the fan...they ran a story in HotRod mag last year on a big block Chevy that showedd a savings of over 30 hp over a stock full time fan on the dyno at peak hp....

 

Just a couple thoughts. The diesel is only turning at 2000 RPM's. If it would turn at 1000 more rpms, like a gas engine, and the fan wouldn't be a flexfan, it might lose another 8-10 HP, putting it right up there with the 25 - 30 HP estimates. It's also possible that the fan that the cummins uses isn't designed the same as an automotive fan. Yes, Diesels make heat, but for some reason, they find a way to move alot of the heat out the exhaust. The power unit type of steady rpm doesn't make as much heat as fluctuating throttles in car engines either, so the fan on the cummings might not need to as radiacal or power robbing as truck fans. Plus, they might have an oversize radiator (thus the oversize fan) just so the engine doesn't have to work as hard to operate the fan. Trucks have space limitations that the power unit wouldnt.

Now with electric fans, Permacool http://www.permacool.com/Catalog/Cat_page16.html
says that a Big block motor needs about 4500-5000 cfm to keep it cool. Weather that figure can be met by the air moving through it while driving, I don't know, but I suppose so. They have a 18" fan that supposedly draws 10 amps and moves 2500 CFM. To me it would seem to be better to use 2 of the 14" fans drawing 9 amps side by side and have a potential for close to 6000 CFM of air moving power. This would probably work even for airconditioned vehicles caught in traffic jam in the middle of a Mississippi summer.

However, depending on your vehicle options and your alternator, even the additional 10 amps could cause a vehicle owner to seek a higher output alternator. Adding both would make it even more probable. If we use the rule of thumb that 1KW takes 2HP gas or diesel engine to make, then a 100 AMP alternator would draw as much as 24HP from the engine. (100amp X 12 volt = 1200W X 2) The extra 10 amp motor would seem to draw an extra 1.2 HP or so it seems. Again, however it seems the gain is that either the electric fan the "cyclone fan mentioned below only draw power when engaged or "ON". Thermo-fans are supposed to work that way, but IMO they fall short of reliability.

There is another type of NON-thermo fan being marketed called the cyclone power fan. http://www.usgear.com/cyclone.htm They also claim that a vehicle fan can rob as much as 40 HP from an engine.

 

Good points- FYI, the fan on the diesel isn't a flex fan and it doesn't have a clutch- I's a fixed-pitch fan bolted on a belt pulley always running at full tilt using "worst case" horsepower. Since the RPMs and load are always constant, I can see where there woundn't be any advantage to using an modern automotive approach to the fan system and that removes a potential point of system failure on a generator that runs unattended- and needs to run as reliabily as possible.

The fan is around 28"-30" in diameter, I have no idea of what the fan's RPMs are, but horsepower is horsepower; per the Cummins engineers, it appears to take 17.7 horsepower of 'fanning' to cool this diesel generating 300 continuous HP.

thanks-

 

If we use the rule of
>thumb that 1KW takes 2HP gas or diesel engine to make, then
>a 100 AMP alternator would draw as much as 24HP from the
>engine. (100amp X 12 volt = 1200W X 2) The extra 10 amp
>motor would seem to draw an extra 1.2 HP or so it seems.


It seems I'm quite off on my calculations here. I remember it was late, but I can't blame it on drinking. Just a decimal point, but it makes a big difference. A 100 amp alernator would draw about 2.4 HP rather than 24. This means that a 10 amp electric fan motor would only draw an additional .24 HP. It still might be be enough of a difference to need a bigger alternator, but it wouldn't draw much off the motor as slikness mentioned.

Tony

 

You're still off, bossman. Check it out: Power= (current)*(voltage).
and remeber, 1 amp * 1 volt is a Watt. 746 watts is 1 Horsepower. Therefore, 100 amps * 12 volts=1200 watts, 1200 watts * 1 HP/746watts= 1.61 HP. You and I both know that a vehicle doesn't run at only 12 volts anyway, as a batter is made of 6- 2.1 volt cells, should be 12.6 before the engine starts, and at 2000 RPM, with a healthy alternator/voltage regulator, the system should charge up to 14.5 volts, and 13.5 at idle. Therefore at 2000 RPM, we hae 14.5 volts * 100 amps is 1450 watts, or 1.94 HP. However, I will admit that there is mechanical loss involved, as there are no machines that can perfectly transform mechanical energy into electrical energy. The point is, electrically driven machines draw dramatically less power than the equivolent mechanically driven accessory. I'm not bustin' on you Tony, I appreciate the technical discussion, but I am fresh on my knowledge on circuits, I'm a Junior Civil/Environmental and Mechanical Engineering student at The Citadel.
John F. Daly III
The TorqueKing

 

Your probably right in the calculations. I was just making a generalization based on observations with home use power generators. They usually are able to produce about 1kw per 2Hp gas engine and sometimes a little better. Amps X Volts = Watts. I guess I should've stated the idea of the "generalization". Great that you have the education with you haveTorqueman, but it's more impressive on a resume than in defending your math or in boasting your qualifications. Not bustin on ya.. Hang loose, the Cummins in question still takes 17+ Hp to drive the fan.
Good success with continued education.
Tony G

 

I think it's interesting TonyG that you came up with close to the same numbers with your generalization. I had never thought about the extra hp to run a higher output altenator, but one thing to consider is that you are increasing the output from 60 amps to 100 amps so the additional hp would be for the 40 amp increase. (I'll let TorqueKing figure that hp out!!)

Anyway, just wanted to let you know that I run the dual 14" PermaCools and they are the highest output for the least amperage that I could find. They are awesome. What is really nice is that I'm theoretically pulling close to 5000 cfm when my truck is idling at a stop sign and that's where I need it most. I run a manual switch on mine and I have the thermal switches, but have not found the time or priority to mount the switches (one for the thermostat and one for the A/C)

TorqueKing, thanks for the kind words the other day, but I get my feathers ruffled all the time. Especially when young upstarts like you are right and I'm definately wrong. I hate that!!! But hey, that's how we learn. I appreciate your efforts in applying all that theory to our practical everyday use. Keep it up!!

 

General ramblings...
Good calcs. Alternators have a 66% efficiency. An alternator typically pulls 3.5 HP from the FEAD.
I do not believe 5000 CFM from 10 Amps. especially at the diameter they are advertising.
Never believe the mags. They are generally accurate in the direction of their thought, but they are also testing components that are advertised in their magazines. Bite the hand that feeds you? Not in business.
An 18" diameter fan on your vehicle pulls ~11 HP when fully engaged. The clutch does not engage until the bimetal spring is activated from the air coming off the heat exchangers (engagement temp is dependent on vehicle configuration).
Ram air has a greater effect above 30 mph than electric fans.
Electric fans are awesome when used in conjunction with engine driven fans because they make up for the deficiency in airflow below 30 mph. AC operation is more efficient.
Electric fans should be used to pull the air through a radiator. They are less efficient when used as pushers, plus they are protected from fan stalling debris (only you can prevent electrical fires).
God Bless the military.

 

The estimated ratings from PermaCool 14" fans are as follows:

14" High Performance Electric Fan
Mounting Area Req'd: 14" x 14" x 3-3/4"
Est. CFM: 2950
Motor RPM: 1800
AMP Draw: 9.5
Fuse Size: 30 AMP

 

Hey slik, I was wondering if it would be safe to upgrade my OEM flyswatter for a flex fan, I've heard horror stories of them coming apart and pitching blades through the hood. Keep in mind, my 302 only spins 5500 RPM, and I want it to stay at 160 degrees. I havn't found an electric fan yet that is rated high enough. I have a brand new 245 AC system (2 windows down, at 45 miles per hour), but I have a 378 Ft*lb, 330 HP engine. I have a 4 row radiator, and my OEM flyswatter puts a tremendous wind over the engine, it'll blow a hat off your head if your standing next to the driver door when the hood's up. I don't want to lose any cooling capacity, when this best fires up for the first time, it's going to make a lot more heat than it did before, in stock trim. Also, where do you wire it into? I don't want to have to flip a switch, I'd like it to run the whole time, but if you wire it into the ignition switch, then it will run even when the engine is off, but the key is in, and the lowest electronic thermostat i've seen is 170 degrees. I'd appreciate your advice Slik.
John F. Daly III
The TorqueKing

 

obviously I was talking about wiring the electic fan setup, if I go that way, I just thought I'd correct myself before I got mugged for talking about wiring flex fans

 

[updated:LAST EDITED ON 12-Apr-02 AT 07:46 PM (EST)]Slikster,
Are those dual 14's on or 351? How did you mount them? Side by side or corner to corner.

Ronbo, Notice Slikness's fans are dual 14' each pulling 2950 or so cfm. Each 14" pulls 9.5 amps for a total of 19 amps. The permacool 18" fan pulls 10 amp and 3000 CFM's If we assume that the current is actually about 14 volts, If we use the "Generator Generalization" that 1KW=2HP we have the following calculation. 19amps X 14 volts= 266 W or (about).25KW. .25KW X 2HP per KW = .5 HP from the engine needed to drive the fans. I think since I've used the generator generalization, I've already factored in the 33% loss that you mentioned. But if not, it's still only .16 HP or a total .66HP more (.5 + 33%) Since you say a fan for a 351 would pull about 11 HP, slick is saving about 10HP to be used elsewhere. This of course is only when the fan is engaged. But the electic fans would also only draw that 1/2 HP extra when engaged.


It does seem strange that you can power fans to cool the radiator electrically with less HP than you can if they are driven off the water pump, but this seems to be the way it is unless there is fault in our reasoning that someone can point out.

Slick,
Any other comments about how it works would be great. Do you ever notice your engine heating? Do you have one set to come on earlier than another or do they both come on together? Any pics in your gallery? Did you custom make the shroud?

Tony