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  #1  
Old 07-10-2003, 12:21 PM
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Question "fan delete mod" popular with BMW ppl

Can some of you guys have a look at this? It seems many BMW people are removing the fan clutch from their cars and the fan assembly completely to gain 6-8hp...some people compensate by installing an electric fan...ummm...isn't this bad for the car? I wonder if it would work for the W124 E420 or other M-B's...knowing the W124 V8's...I am guessin' it would overheat like crazy...anyhow, it seems to be very popular...just bringing it up to see what is the view on this with the M-B crowd...there are two links I found on the subject:

directions for BMW's "fan delete mod"

installation of electric fan
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  #2  
Old 07-10-2003, 12:28 PM
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You can bet any electric fan they install won't be as powerful as the 6-8 hp worth of air movement by the mechanical one. If you are pulling a steep grade at 75mph in 100+ weather with the air on and a full load of party folk, the difference might be between making your destination unscathed - or a detour on the back of a tow-truck to the service bay.

Steve
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  #3  
Old 07-10-2003, 02:26 PM
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Do a search I think a couple of people did this here.
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  #4  
Old 07-11-2003, 02:02 PM
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The advantage of an electric fan is that you are no longer dependent on engine RPM, for example, stopped in traffic when you need the most air flow, the mechanical fan is not very effective.

Also, above about 4000 RPM, the mechanical fan is disengaged to protect it, no need to do that with an electric, although at 4000 RPM the car is probably going fast enough to not need any help from the fan. On a W124 MB, after about 25 mph, no fans are needed.

With two electric fans, one or both can be turned on as needed.

But in an MB, you will probably have to upgrade the alternator as well. Do a search and you will finds some discussions on this topic.
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Last edited by zafarhayatkhan; 07-11-2003 at 08:07 PM.
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  #5  
Old 07-11-2003, 02:25 PM
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<>

I have often toyed with the concept of modifying aux fan trip to the speed sensor circuits..
Say, at zero to 15 MPH specs...
Also have considered speed sensed high fan for a/c at stop/idle conditions ... this would be a simple speed sensed relay paralleling the dropping resistor [ low to high speed fan] when in traffic/stop lights, etc..

You will notice that Benz is now using electric fans [ puller] and also using a/c compressor synced activated aux fans....
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  #6  
Old 07-11-2003, 07:33 PM
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Another thought on this is that, there is no such thing as free lunch. If you take the fan off the drive shaft and replace it with an electric fan, the electric fan must be fed by the battery which must be recharged by an alternator. The alternator is a load to the engine.

------------------------

Could this be so? It seems to me that the alternator is being spun by the belt all the time whether the car needs the current or not. It's not a so much a free lunch as it is just eating one of a number of lunches that might otherwise be thrown out and not eaten.

The alternator loads the engine the same amount whether the car uses the curent generated or not. It's not like the A/C compressor, which spins freely when not needed and engages the cluth and loads the engine an extra amount when it is needed.
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Old 07-11-2003, 08:04 PM
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"The alternator loads the engine the same amount whether the car uses the curent generated or not."

No way! The power consumed from the engine by the alternator is in proportion to the square of the current produced! You cannot compare it to a clutched, relatively constant power consumer such as the a/c compressor. The alternator will only produce the current demanded of it by the electrical system at the moment. Its current rating is a MAX available, and that only above a specified rpm. On a cool day when the only consumer is the ECU and ignition, injection components, the alternator will produce very little current.

Steve
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Old 07-11-2003, 09:15 PM
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The more the current draw on the alternator, the more resistance to roatation it produces and thus more "drag" from the engine. When you turn more electrical consumers on, it does decrease your power available from the engine to turn the wheels, althought not by a terribly large margin.
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  #9  
Old 07-11-2003, 10:11 PM
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How does the alternator put a drag on the engine? Do the little brushes grab the armature more tightly? Does flow of electrons make the armature of the alternator harder to turn?

I mean, the alternator turns at the same rate, plled by the belt, whether the car needs current or not.

Where do the electrons come from, anyway? Why does it seem we don't run out of them?

I suppose I should have taken a course in electricity.
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  #10  
Old 07-12-2003, 12:45 AM
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The basic laws of physics >>

You can never get more energy out than you put in..
If you could, you would attain perpetual motion...

In this case , that would be a motor turning a generator
to feed the power to run the motor...

Does not work due to output being less than load input required......
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  #11  
Old 07-12-2003, 03:59 AM
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The Science Museum in London has a rig where you turn a handle that rotates the armature of an alternator. It is connected to some light bulbs. When the bulbs are turned on you can feel the drag.
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  #12  
Old 07-12-2003, 04:11 AM
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Same deal with a WW2 Signal Corps generator .. one guy turned the handles while the Radioman turned the radio on...soon as he
loaded the radio on , you could see the generator guy start grunting......
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  #13  
Old 07-12-2003, 06:25 AM
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I see a different approach to this question.

At high speed there is no requirement for a fan because the air flow provides all the cooling that is required. However, the higher the revs, the more power an engine driven fan consumes. So it is essentially wasted. In addition to the wasted power, we pay for it with additional noise.

At idle, there is no flow of air through the front of the car, so some sort of cooling is necessary. An engine driven fan is a simple solution, however, at low revs it does not produce much wind effect. At the same time, it consumes very little power.

Cars mostly overheat at idle, so an electric fan needs to generate the greatest cooling effect at idle. However, this is the time that the alternator is also turning slowly, and has limited capability to produce enough power. The alternator would impose additional load on the car engine, and may well drawn additional reserves from the battery.

At high speed, a thermostatically controlled fan would most likely switch off, and thus consume no power.

Having driven a Jaguar that had twin electric fans, I can attest to the benefit of reduced noise as revs increased, at the expense of more fan noise at idle. When stopping after cruising at highway speeds, the fans would be silent, but would gradually pick up speed as the car idled.

So, your driving habits and climate where you live may help to decide whether you should convert to electric. If you idle in traffic a lot, the electric fans should cool better, be noisier and consume more power. At speed, electric fans would be better than mechanical fans in all these aspects, because they would probably be freewheeling.

Where engine driven fans win over electric fans is where the engine is working hard at low vehicle speeds, like towing, stop start traffic, etc. However, this is also when their noise is most apparent.

No doubt, car manufacturers spend quite a bit of time working out the best compromise to satisfy these different requirements and limit the power usage and noise. To simply go out and buy an electric fan off the shelf would oversimplify all the engineering effort that has gone into the design, and may not fully satisfy the essential requirement as well - cooling.

Hopefully these ideas have given people food for thought.
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  #14  
Old 07-12-2003, 12:40 PM
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The main concept of viscous fan was to NOT use up power..
It was a design to add HP ..[over direct link fan]
They free wheel when not called for and have an rpm cut-out besides.
Even at idle , they push a good amount of air , --the problem is they tend to have a high cut-in coupling temp... the makers are trying to get gas mileage to the point of walking the safety line...

Electric must be the best compromise for low rpm, as the newer Benz have gone electric, no more mechanical fans..
Although the electric system has to be up for the job,I think electric is definately a better system...specially at low Rs and
low ground speed ...

An interesting way to look at airflow/cooling sytems is the fact that the aux fans are called for After the coolant temps start to excede the cooling systems normal capacity. They then come to the rescue by adding more airflow..
If airflow was kept constant , regardless of rpm/speed,
temps would be more stable..so an airflow sensed type design
would regulate the fans to keep a/flow the same , regardless of vehicle speed.. seems to be pretty easy to do with electric fans and speed/air flow sensor coupled with ect paremeters..
just another way of controlling engine temps , but coming at it from a different angle... seems we always get into trouble at Low Rs/low speed/traffic conditions.
This would eliminate all those...and BEFORE hand
NAAAAHHH !!!
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Old 07-12-2003, 04:47 PM
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Err, 30 amps @ 12 volts makes 360 Watts. I seem to recall from my schooldays that one horsepower was 746 Watts, so we're talking about half a horsepower!. The problem with engine driven fans is how to provide adequate airflow at idle revs without wasting power at high revs. The viscous coupling is a compromise, electric fans are best as they run at a constant speed.

Check out http://www.kenlowe.co.uk
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