Battery not charging, how to test alternator?

[Campbell0240 0]

Hi guys, i've recently replaced my 2.9 vr6 engine out f my corrado with a 2.8 stage 2 supercharged lump.

I replaced the battery at the same time and its lasted some time but recently as i've ben driving back and forth the garages its started to lose charge it seemed to completely run out and when i started it after charging it for 15 minutes it didnt seem to last anymore than 5 minutes it would cut out as the car was going?

The garage put a voltmeter across the battery to show it losing charge i just wondered how i test the alternator or any common problems that occur?

I do have a spare alternator off my 2.9 vr lump but i believe its a 70A not a 120A thats on the 2.8 i've put in? would that be sufficient?

Which leads to the next question how do i properly tension and release tension from the SC on the belt?

[mannie 0]

with the engine running,take a reading with a volt meter across the battery, if the alternator is ok you should have more then 12V output.

[apd 0]

i bet you have little tension/contact on your alternator pulley.see my post on belt slippage-might help!

[Campbell0240 0]

Cool didnt think of that, how am i supposed to take tension on and off properly? havent had a proper look and i dont fancy just diving in unless i miss something?

[spindat45 0]

An alternator that is charging properly should give you a minimum charging rate of 13.7/13.8 volts when tested across the battery with the engine idling (using a volt meter). Any less than that and you will be using more juice than putting back in. This will usually rise to around 14.5 volts on fast idle. As advised also check belt tension.

Kevin

[dellert 0]

To check tension. There are two lines on the tensioner, with a little arrow pointing in between them, if all is well. If all is not well the arrow will be outside the two markers.

[Bazmcc 0]

My battery idles at 14.4 Any lower than 14 and it's borderline.

Baz