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Steve_D

Original Poster:

9,179 posts

138 months

[news] 
Wednesday 18th April 2012 quote quote all
Does it matter which direction an alternator spins?

We have a very tight installation on a kitcar and may need to install the alternator in front of the engine which would spin it in the opposite direction to normal (if there is a norm).

Thanks in advance

Steve

Max_Torque

6,882 posts

97 months

[news] 
Wednesday 18th April 2012 quote quote all
The answer, is of course, a resounding "it depends"....... ;-)


If there is a one way clutch built into the drive pulley (modern alternators use this to relief torsonal vibration loads on the FEAD system during things like WOT at low rpm, gear shifts or even ABS brake events etc) then obviously this will not allow a torque direction reversal.

Assuming it is an old Alternator and has no one way clutched pulley, then you should be able to spin it backwards, howeverm note a couple of things:

1) the cooling fans built into the rotor will not be quite as efficient as the blade angle will be wrong. However, these fans are rated for full output in 50degC heat, so unlikely to be an issue in a kit car (assuming it hasn't got much Electrickery installed!)
2) if it is a s/h alternator, the field energisation brushes will have worn somewhat lopsidedly, running it backwards may initally result in a slightly funny noise as the bushes wear the otherway



So in general, it shouldn't be a problem to run it backwards as the individual winding (phase) output AC power signals are passively rectified and so don't care about phase order!

Steve_D

Original Poster:

9,179 posts

138 months

[news] 
Wednesday 18th April 2012 quote quote all
Thanks MaxT

Further info...It is a new aftermarket 40amp unit so no issues with clutches or existing wear patterns.

The builder had installed the alt. further back due to lack of space and fitted it with a jack shaft running in a pillow block bearing just behind the pulley. The whole arrangement would have been almost impossible to keep aligned. Net result was a broken mounting at the bearing and a destroyed alt.

Time to design a new mounting.

Thanks again.

Steve

Mr2Mike

11,439 posts

135 months

[news] 
Thursday 19th April 2012 quote quote all
Steve_D said:
Thanks MaxT

Further info...It is a new aftermarket 40amp unit so no issues with clutches or existing wear patterns.

The builder had installed the alt. further back due to lack of space and fitted it with a jack shaft running in a pillow block bearing just behind the pulley. The whole arrangement would have been almost impossible to keep aligned. Net result was a broken mounting at the bearing and a destroyed alt.

Time to design a new mounting.

Thanks again.

Steve
Rather than redesign the entire thing, could you install a coupling that allows a some degree of misalignment? e.g. like this

Steve_D

Original Poster:

9,179 posts

138 months

[news] 
Thursday 19th April 2012 quote quote all
Mr2Mike said:
Rather than redesign the entire thing, could you install a coupling that allows a some degree of misalignment? e.g. like this
Yes that type of coupling is a possibility and keep the jack shaft arrangement but the rest of the mounting is so badly made I'm more inclined to thow it all in the scrap and start again. We will see.

Steve

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Huff

1,440 posts

71 months

[news] 
Thursday 19th April 2012 quote quote all
IIRC some Honda engines spin 'backwards' so presumably their alternators are also setup for anticlockwise drive. Might be worth finding a suitable one off a pranged vtec Civic to make any concern go away.

Edited by Huff on Thursday 19th April 21:39

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