another alternator question

[waynos 0]

i posted a while ago bout having a battery drain. i ruled out the alternator because it was a new rebuilt item. months have gone by and i have the same problem with the battery going flat again. i did a test today with the engine runing (lights, radio and heater on) and im getting a poxy 12.37 volts. this isnt right is it?

[dr_mat 0]

Correct. You want to see 13.5 or more with the engine running, even if you have electrical drain (lights etc).

[waynos 0]

just an update,last night i did a few tests with my mate.

 

we found out the stereo hardly drains the battery when running (15 inch alpine sub/amp , alpine h/u and components) so thats a relief

 

the windscreen wipers hardly did anything either, however the power hungry feckers were the rear heated window, heaters and lights! didnt get any exact figures as it was raining and i wanted to get inside. but i remember at some stage the voltage readout dropping to 12v and somtimes even 11.5 when two or more things were on at once.

 

im well shocked about that.when nothing is on the voltage is about 13.5

 

maybe its time for a bigger alternater , why did vw even bother fitting such a low rating one?

[dr_mat 0]

Well what car do you have, and what rating is your alternator? They shipped 120A alternators on VR6s with air-con. It could just be that your alternator isn't working right.

When nothing is running, the alternator output on my VR6, for example, fluctuates between 13.8 and 14.2 volts.

[waynos 0]

its a 1.8 16 valve. the alternator is a pesky 65 amp rating! the highest ive seen voltage wise is 13.5 with everything off. a vr6 alternator wouldnt fit would it? if it did would the 120 amp rating fry my wiring?

[dr_mat 0]

The rating is simply the *capacity* of the alternator. It won't actually deliver 120 amps unless your car's electrics demand it.

Note, however, that the bigger the alternator the more it'll sap the engine's power. It probably won't be very noticeable but don't say we didn't warn you .. :)

Anyway, I suspect that what you have there is a faulty alternator, not necessarily an under powered one.

[Phil K 0]

Are you measuring the current from your alternator or the voltage level at the battery when you're doing these tests?

 

I ask as having the VDO gauges in mine I see same kind of voltage drop with the lights, heaters etc... but thats reading from the battery and isn't a reflection of if the alternator is doing it's job properly...