Alternator question 1

[reidh]

A very quick question that hopefully somebody knows the answer to. Does the fan integral on an alternator pull air from the pulley side through the back of the alternator, or vice versa? Is this a standard on all alternators?

 

[JWaterstreet]

Ah, finally a post that I have some first hand expertise! (I used to work for an alternator manufacturer)

Virtually all pull the air thru the back of the alternator, and the air exits thru the front of the alternator via the fan blades. There have been loads of specialty alternators that have been sealed (mainly military), oil cooled (found on transit buses & old fire engines), and reverse fan designs (fan on back of alternator; not on pulley end), but the typical car and truck alternator is the generic, fan in front, pull air through design.

This has been a headache in the last few years with the high heat generated by the latest diesels, as the alternator can pull already hot air into the back.

 

[LordMalaK]

Thats interesting as the back of the alternator is sometimes a inch or 2 from the exhaust pipes where the air is hottest and the front faces the cooler incoming air thats gone thru the radiator. But as some have a cover on the back connected to an air duct it makes sense that on that particular alternator, the air does indeed come from back to front.

I submit that some intake air from the back, and others are just the opposite depending on who made em.

 

[WGJ]

Never doubted JWaterstreet - the fan on the front of most alternators appears to be a simple centrifugal device, drawing air in near the shaft and blowing it out around the periphery.
Don't forget that a lot of automotive stuff has always been designed down to a price rather than up to a durability or performance.
Doing it 'the engineer's way' might well get cooler air through the alternator but it's cheaper just to bung a bit of cheap ducting on the back.


Bill

 

[JWaterstreet]

And the centrifugal fans are designed for maximum flow in one rotation direction. The company I worked for sold most of its alternators into mostly off-road applications. We used to have numerous cases where the system designers used the wrong rotation fans and couldn't understand why the alternators kept burning up. And occasionally came across an "engineer" that thought that they could "push" the air through the front of the alternator by rotating the alternator the opposite direction than it was intended.

 

[statorwinder]

Internal fan alternators draw air from the side (front & back side of the housings),Thats the reason for all those holes in the housings & force it thru the back,The front fan draws air in & forces it across the stator & rotor
The rear fan draws air in from the side & whats left over from the front fan & forces it over the rectifier & regulator
Most are designed for 1 way operation.This is determined by the angle of the fins
internal fan alternators have been around for a long time
example is chrysler automotive

External fan alternators generally have solid cases & draw air thru the back,altho a few designs (12si 94amp delco) have some air passages in the sides,,These also have a squirrel cage designed fan.

Universal type external fans are also used for CW or CCW operation
These type fans have streight fins & mostlt found on motorola & leece neville alternators

George

 

[BCjohnny]

Statorwinder..............

Internal fan alternators actually draw the air in from the front and rear and, via the centrifugal fans, expel it through the stator windings. This is how they are cooled. The fan on the rear of the rotor often has more/larger blades, obviously biasing the air flow to the rear, to draw air over the Regulator/Rectifier assemblies, and push it out through the stator windings.

Some do however have bi-directional ("straight") fan blades, though only the French made Delco seems to use this method, at the rear. Does this help explain the relatively poor reliability of this unit, that regularly suffers terminal rectifier failure?

LordMalaK..............

Have you come across the increasingly specifed Water Cooled units, that cool via the engine coolant system? Complete with their lack of finning and with an integral water jacket? Normally these are fitted with one way, sprag clutch pulleys, not solid, that when they fail (and they do, with no predictability) do so "Large", sometimes taking the radiator too. Unfortunately they are increasingly being fitted to more mundane units. Yes I know the theory behind it...........

John.

"It's not always a case of learning more, but often of forgetting less"

 

[statorwinder]

BCjohnny......
Thanks
I knew i had made a mistake seconds after i hit the send key
Water cooled american alternators are only found on cadillac , Bosch also makes this alternator for some of the european vehicles (,,,never worked on one yet but do have some cores in stock....
The delco alternator has magnets between the claw poles
and is polarity sensitive when testing field current draw,results are lower maximum output if not polarity tested the right way

clutch pullys seem to hold up,Haven't seen one yet go thru the radiator,generally they lock up or just become noisey


George