Alternator query

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VR6Turbo
Posts: 329
Joined: Wed Mar 17, 2010 9:24 am
ECU Model: S80 Pro
Firmware Version: 62

Alternator query

Post by VR6Turbo »

Are general car questions allowed? There's probably a helluva a lot of general car knowledge contained within this forum that can be tapped into! :D

Anway, I'm gathering parts for my engine transplant and one of the bits I needed to get was an alternator from the donor car. It's a 140A Valeo unit and the pulley turns fine in one direction, but slips in the opposite direction. It's clearly deliberate but I don't know for what purpose? Anyone know?

Cheers
razzor
Posts: 44
Joined: Wed Aug 03, 2011 3:50 pm
Location: Durban, South Africa

Re: Alternator query

Post by razzor »

came across that not so long ago on a import suv, cant recall the name. the alternator has a oneway bearing of sorts. remembered it because the electrician we gave it to called it a flipped bearing.
he told us its getting common.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: Alternator query

Post by stevieturbo »

What do you mean by slips ?

Some alternators may have a clutch type device in them so that when load is removed, they free spin. SO I guess that could mean rotating it the opposite way means it just free spins ?

But most alternators are just a fixed shaft.
Wally
Posts: 64
Joined: Wed Aug 10, 2011 10:10 am
ECU Model: S80 Pro
Firmware Version: 51
Location: South Lakes, UK

Re: Alternator query

Post by Wally »

A lot of the newer cars/alternators have this feature. As the alternator outputs grow so does the weight of the rotating parts in the alternator, this then would cause the alternator to try and drive the crank pulley when the engine is in a sharp throttle off situation due to the alternators momentum. This then in turn can overcome the automatic tensioners fitted to a lot of vehicles and hence the belt becomes slack and it can even cause it to throw the belt. I have seen this happen when the one way clutch seizes. In the few cases I have seen, the belt will flap about a lot and you can see the tensioner moving as you accelerate and decelerate, new pulley and all is Ok again.

Wally
VR6Turbo
Posts: 329
Joined: Wed Mar 17, 2010 9:24 am
ECU Model: S80 Pro
Firmware Version: 62

Re: Alternator query

Post by VR6Turbo »

Cheers Wally, that makes perfect sense!
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