Alternator Fault on my Rangey

Hello again folks,

so i've been having problems with the car and starting to get them sorted! WELL this morning i went out to the shop and up popped alternator fault on the dash! Looks like a brand new alternator thats fitted. What else should i check.

And how tight should the auxiliary belt be? I thought it seemed a little over tight. Theres no movement in it hardly.

Cheers

Chris

there wont be any movement in the belt, its auto tensioner.

try the connections on the alternator and battery. failing that you'll prolly find the connections on the becm need a push or a clean.

after that its gonna be alternator that has a fault!!!

gavbriggs said:

there wont be any movement in the belt, its auto tensioner.

try the connections on the alternator and battery. failing that you'll prolly find the connections on the becm need a push or a clean.

after that its gonna be alternator that has a fault!!!

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i agree with gav,just be carefull what you do with the battery and the BECM incase you get the dreaded lock out.

you said it looks like a new alternator? does the alternator charge light (little red battery icon in the dash) come on when you turn the key? if its on all the time then your alternator is not charging. if it never comes on at all then what you have is technically an alternator fault but not a faulty alternator(!). basically some aftermarket alternators' rectifier circuits are a bit off and don't send the right signal to the computer to say they are charging or working so the car thinks the whole thing's wrong but meanwhile in actual fact its charging the battery just fine. mine does this and after i figured it out i've left it as it is.

best thing is to check voltages at the alternator terminals with and without load and then you'll be sure. had a mate do this for me so can't tell you what the expected values should be but sure you can find 'em somewhere in here.

sure i commented on this somewhere in the forum, dunno where tho

[ame="http://www.youtube.com/watch?v=WU7EHaScH_o"]YouTube - How to check the alternator[/ame]

that will NOT test an alternator - it does NOT test for ripple voltage.

take yo motor to any decent garridge (or Halfrauds) who will test it for free.

i ant watched the vid but was told by a qualified mechanic to put load on the battery, i.e forcing alternator to charge and see what voltage is at the battery!

I have recently seen two alternators which put out good volts, but next to no current. One had two wires broken inside the alternator - so a pure voltage check is not a definitive answer. Both the defective alternators showed up as faulty on ripple voltage.

so how do you test for ripples?

Ice cube

thats nipples!!

gavbriggs said:

thats nipples!!

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Oops:doh:

Use a Bosch BAT121, or an oscilloscope?


or (sorry Si) go to Halfrauds - they will test it for nought.

so theres no way to test for ripples with a multi meter???

gavbriggs said:

so theres no way to test for ripples with a multi meter???

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Put your digital multi meter on 20 volts AC instead of DC and connect it across the alternator output, not at the battery terminals. If the alternator is producing ripple free DC then you will get little or no reading, keep dropping the voltage on your multimeter and if you are still getting no reading on the 2 volt range then you have little or no ripple. If there is ripple, the multimeter will see it as AC of sorts and will produce a reading which will depend on the frequency of the ripple and the amplitude. The output of vehicle alternators is pretty messy so I would always expect a small amount of ripple to be present as it starts off as AC which is rectified to DC by the diode pack. The switching speed of the diodes (quality) will determine the basic level of ripple present.

whats the AC ripple limit on Alternators?

nobody likes a smarty pants!!!!!

The Mad Hat Man said:

whats the AC ripple limit on Alternators?

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Don't know, but a good battery will absorb quite a lot of ripple which is why the test should be done at the alternator. A duff diode is easy to spot on an oscilloscope as is a duff winding just by the uneven pattern of the ripple

gavbriggs said:

nobody likes a smarty pants!!!!!

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Sorry, electronics and air are what I do, not particularly to do with vehicles but the principles are the same.

ha!!!