Bi-directional Leece Neville Fan?

[Geno]

When I bought the alternator they said it had a bi-directional fan. About halfway through today's work I noticed an arrow on the fan and it's pointed the wrong way. Is this fan bi-directional or not? The finished unit will be a  portable 12v battery charger.

Thanks, Geno

[mobile_bob]

it is not bi-directional

depending on how many amps you want out of your alternator will dictate whether or not
you can use a bi-directional fan or not.

the directional fans are optimized for the specific rotation they are noted as, and as such
pull more airflow through than the bi-directional fans.

if you want to work the alternator hard, you might want to order the optional directional fan
that is made for reverse rotation applications

bob g

[mobile_bob]

or you can reorient the alternator mounting so that the thing is driven in the direction of your fan?

might be easier, and looks like you could have room to do it with your frame

bob g

[Geno]

I do have room and considered that option. However it would mean grinding off and reversing the alternator bracket contraption and further pissing me off for having missed the arrows. I also looked at reversing the engine but the exhaust would be pointing the wrong way. I'll check prices on reverse fans and decide based on that.

Thanks, Geno

[XYZER]

Geno,
Mine also came with a directional fan. I ordered a bi-directionl fan from a Leece Neville alternator dealer in Portland Or. It has flat blades that cools either rotation. Maybe not as efficiant but good enough to keep a slight breeze on my radiator and keep it cooler than without. I might be able to get the p/n off the pulley to help out. Let me know.
Dave

[Geno]

I had a computer service call today at a Peterbuilt shop. I asked the guy about the fan and he looked through his box of cores. No luck but his Father worked at the local, heavy truck parts distributor which was also the Prestolite vendor in Albany NY. He called his Father who found a bi-directional fan in their box of cores and he had it on the counter waiting for me, no charge! His store was also only a 1/2 mile from my next service call.

I may not get quite the airflow with a bi-directional fan but in this app. I'll never be pushing it past 1/2 capacity anyway.

Thanks, Geno

[mobile_bob]

they used the bi-directional fans on that alternator on the earlier versions which were 120, then 130, then 140amp units
they went to the directional fan when the went to 160amps

to get a reverse rotation fan you would likely have to go directly to prestolite/leece neville, because they are not used in trucks
and any other equipment except for marine applications where you have two counter rotating engine's, so i expect the marine
folks might have access to one, or

the oil field applications where they build two engine drives which again are counter rotating, there might be access to the fans
there.

probably rare as hens teeth anywhere else.

bob g

[cujet]

A different take on centrifugal compressors and fans.

The angle of the vanes is not at all critical. Common sense would dictate that the vanes should be swept into the direction of rotation on the inducer. Swept back on the tips.

However, testing shows that airflow and overall performance can be better with forward swept tips. In fact, you will see some high performance fans and compressors with this very design. A forward sweep provides MORE AIRFLOW (contrary to what you would think).

The direction of the inducer has little affect on overall performance (generally on the order of a few percent from none to best). Remember, the pressure rise (and therefore airflow) is created by the mass of the air moving outward through the vanes of a rapidly rotating centrifugal compressor.

I'm not going to claim that it will work just fine (although, I suspect it will). But, if it were me, I'd try it before I made any major changes. You might be pleasantly surprised.

[cujet]

http://books.google.com/books?id=Euo81Pjuj-YC&pg=RA1-PA11&lpg=RA1-PA11&dq=forward+swept+centrifugal+compressor&source=bl&ots=sz3HBX9P3X&sig=K0W04hAZQr_ffCyvInXkeu830nA&hl=en&ei=n8BLS5LGJMKVtgeN3LDkDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAYQ6AEwAA#v=onepage&q=forward%20swept%20centrifugal%20compressor&f=false

[mobile_bob]

thanks for the link to the book Cujet

i have been spinning both my alternators backwards to the directional fan, one is used only for charging the starting battery
so there is little need for much if any airflow

the other unit has been run up to 2.9 to as much as 3.5kwatts but 2.9 is about all i am comfortable with the fan turning backwards

it pulls air as it should just not as much as it would if it were spinning the right direction.

however, "not as much" is a subjective term, in that i have no real way of testing the benefits of a reverse rotation fan, because
i too don't have one.

on the project x alternator, because it will be running at near 6kwatt, i am considering mating a high flow axial fan to the rear of the alternator
to help stuff more cool air into the machine, i will also be remote mounting the rectifers so they won't be adding to the heat load of the stator.

i have also thought of making a ductwork to take the exhaust air from my st7.5 and ram it into the rear of my high output alternators,
they are so closely located it really wouldn't take much to manifold them to the st head.

airflow for component cooling gets to be an art form all to its own if you are pushing the design limits of the components.

bob g

[cujet]

it pulls air as it should just not as much as it would if it were spinning the right direction.

Are you sure? As I mentioned, it's unlikely that a centrifugal fan will have significant flow changes due to operation in opposite directions. It's the diameter and speed that are key factors. Not the design.

[mobile_bob]

cujet:

no i am not sure of anything, all i know is what i read in the engineering from prestolite

they used the straight cut fans up to 140amp units, and when they announced the new 160amp units
is when they also made the change to directional fan use.

the reason reportedly was the directional fan was able to move more air to provide for sufficient cooling for
the higher output of the new alternator.

i just assumed it maybe pulled 10-20% more airflow at the same rpm over that of the earlier straight cut fan.

next time i get in to their engineering dept i will ask what the increase in airflow is, if any and report back.

up till now this was something i catagorized as "something i accepted without proof", might be prudent to
ask and find out if it is actually something that is significant or just marketing hype?

the industry is so competitive that it is hard for me to imagine that they would spend the money on a directional
fan if it didn't improve airflow signficantly?

bob g

[veggie]

Forward sweeping vanes work...but only so far.
A forward sweep of more than say 5 deg. from straight is about the max., after that the impeller cavitates.
The problem with most of the alternator fans is that they have A] curved vanes which are optimized for one direction, or B] have vanes which are angled much more than 5 degrees and tend to be very inefficient in the opposite direction.

If there is someone out there who has run a 10si or 12si delco in the opposite direction, please pipe in and let us know how it's going.
I have a 12si that I want to mount on my Listeroid and the best available mount spot would have it running in the wrong direction.
I don't mind doing this, but I would like to know if the unit can cool itself at 4500 rpm putting out 50 amps.

veggie

[mobile_bob]

from everything i have read the delco alternator has enough problems with cooling at higher outputs even if turning the
correct direction and they fail fairly quickly if turning the wrong way.

the cs130 gets so friggin hot in operation (when called to charge hard) that it will start to melt the varnish on the outside of the
laminations and will become sticky to a rubber glove.

they also warn that the battery must be fully charged before you startup the engine after installation of a new alternator, this alone
seems like a warning to me if one were to use it for charging a larger battery bank that is down on charge.

not sure which one you are planning to use, but i would limit any long term charging to not much more than 50% of rated capacity
and i would highly recommend turning it in the direction indicated by the fan.

of course you can try to push this recommendation and who knows maybe it will work just fine? but it is unlikely that the lifespan will
be enhanced.

bob g