Fiesta Mk4 battery / alternator still...

peter212693 · 22 Sep 2009 at 19:48

Hi all,

My mum is still having alternator problems i think. There is 12.5v across the battery which is fine. When I start the car the voltage drops to about 12.1v untill 3 or 4 minutes then the alternator will kick in just, giving about 13v maximum.

Ive changed the alternator for a 2nd hand one and its exactly the same (I know the newer alternator could be faulty to). Its a MK4 1.3 2000 reg. Its not the endura engine ive found its the CVH.

Someone told me to check the voltage with the +ve of the multimeter on the battery feed from the alternator and -ve on the battery and I should have the batterys voltage which I do.

Can anyone help at all?

Thanks

Matt82 · 22 Sep 2009 at 20:04

there will be a live from the alt to the starter or directly to the batt. make sure the connections are good/clean and no broken cables. make sure the earth from the battery to the body is good too

do you have access to another battery? i suspect a very duff battery could produce odd results like that too

peter212693 · 22 Sep 2009 at 20:10

This is a brand new battery its about 1 month old mate

Matt82 · 22 Sep 2009 at 20:14

check over the wiring. clean up the connections with wirewool. spray white grease is meant to keep em clean nicely and definately check that earth too

peter212693 · 22 Sep 2009 at 20:17

I will give them a good clean when I get change again. Would the earth problem cause it to only start charging after a few minutes?

Clarkey · 22 Sep 2009 at 20:18

12.5 isn't really 'fine', it's low. Data from Optima batteries website..

6. Battery Testing To measure voltage, use a digital D.C. Voltmeter.

You must first have the battery fully charged. The surface charge must be removed before testing. If the battery has been sitting at least several hours (at least 12 hours) you may begin testing. Alternatively to remove surface charge the battery must experience a load of 15 amps for 2 minutes. Turning on the headlights should do the trick. After turning off the lights you are ready to test the battery. This is a general table, different battery types vary slightly.
State of Charge Voltage
100%
75% - And as low as you want to go!
50% - Deep Cycle only!
25% - Your battery WILL suffer damage...
less than 5% - Discharged

12.7+
12.4
12.2
12.0
11.9

Anyway I strongly suspect the alternator is duff, assuming you have checked the wiring is all secure. You should be seeing at least 14v across the battery as soon as the engine is started.

peter212693 · 22 Sep 2009 at 20:23

I think it was about 12.6v when I started faffing so with me starting it a few times it has dropped and obviously isnt charging. It just seems odd Ive got the exact same results on the "new" and original alternator.