How do I check alternator charge?

[outlaw7]

My S4 is reluctantly turning over in the cold mornings. On Tuesday my battery was a little drained reading about 11.12 and wouldn't turn the engine over. I charged the battery to 12.96 and it started fine yesterday morning, but not so well this morning.

I'm commuting 12 miles a day to work and back, so I reckon there just isn't enough mileage to charge it properly, and the cold doesn't help. Usually it's fine in the warmer months.

So it's either that or the alternator isn't charging properly. Can somebody please tell me how I can check there is a feed coming from the alternator?

thanksmuchly
Ben

[moor-ph0]

Hi,
Check out this link:
http://www.jetav8r.com/Vision/Stator/Stator.html

Explains in detail how it works and what's required to test it.

Geoff

[Zimbo]

Basically, just check the voltage across the battery terminals with the engine running and the lights turned off - should be about 13.8 ish V if it's charging. They're prety reliable, I'd be surprised if it were faulty, far more likely to be a dodgy battery.

[Scotty]

if your still on the original battery id not be surprised

the 'classic' problem in this area would be the reg rec unit under the seat

check the connectors on this bit and also the yellow wires from the alternator for signs of having melted

when my reg rec unit bust there was sign of damage on the underside of it (though that's an un-usual occurrence)

you can test out the altenator bit with
resistance between the yellow wires (engine off)
bugger all resistance between wires and infinite to earth

Vac between yellow wires (engine running)
there should be about 30-50 Vac at a few k rpm

oh if you electrocute yourself that's not my fault :shocked:

oh I should point out the checking of the alternator is based on the two yellow wire (single phase) alternator rather than the 3 wire one on the S4
though I cant see why that should make a difference

[Starter Sprag]

As Zimbo says

and to add,

The battery should give 12.6V DC when standing, 12.5 or 12.4 is no good

Don't take a reading after charging because it will be falsely high

To test charging system/circuit,
Engine off >12.5 V DC
2500 RPM >13.5 V DC
5000 RPM <14.8 V DC

Make sure battery connections are clean and tight
Invest in an Optimate battery tender

[retskcid]

you can test out the altenator bit with
resistance between the yellow wires (engine off)
bugger all resistance between wires and infinite to earth

Vac between yellow wires (engine running)
there should be about 30-50 Vac at a few k rpm


I can add that there should be continuity between all three yellow wires (combo of any two) which I guess I should check now that I have no Vac at all between the yellow wires....

*edit*

I have continuity and very little resistance. I believe I had my meter set to DC instead of AC so I need to recheck alternator output.