Ford focus potential alternator issue

31 Oct 2019
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United Kingdom
Hi all,

Currently having some battery issues with my ford focus. The battery light will come on after a while of driving and eventually the battery died while i was driving when i had to brake.

i went to halfords and they replaced my battery for free and the car was fine for a couple of long drives, 1 of which was a late night drive of 6 hours with head lights, air conditioning on and music with no battery light and since then a couple of short drives later around a town i have noticed after about 20 to 30 mins of driving the battery light will come on again.

I have fully charged the battery with my battery charging kit and i have done some tests on the battery.

when the engine is off the battery is sitting at 12.54v.

when the engine is turned on the battery is sitting above the required range at about 15.3v.

i need my partner to come home later and i can test what the voltage will be when the car is being at 2000 rev and what the battery will be when i have a current drawn from the AC, Head lights and other things ETC.

I believe it could be the regulator inside the alternator but im not 100% sure as i have only started reading up about alternators today and some advice from someone more experienced would be appreciated.

car details:
Ford focus 2011 automatic
45k miles
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For sure, the charging voltage is on the high side, its better to see around the 14.5v mark and that shouldn’t fall much below 14 with an electrical load applied.
If you could rig up a voltmeter which you could see when the charging light comes on would be handy - I have a device that plugs into the fag lighter that does this.
The mileage is a bit low for a failure, I have to say but like you I would expect the voltage regulator.
It doesnt hurt to clean the plug in the back of the alternator though, and give it a spray with contact cleaner.
John :)
Thanks for the reply john.

The only bit of test kit i have is a B and Q own brand multimeter, the most basic you can really get. I cant actually get to the terminal ports on my alternator as they seem to be burried down inside the hood and not easily accesable without removing components (Or im just blind). Is changing a regulator going to be a garage task or something i could crack out in an afternoon with a bit of reading up you think?
I had the same problem a few years ago - Ford Focus would start up, alternator light went out but came back on after a minute or so. I fitted a new alternator and got the same symptoms so I got an auto electrician in. It turned out to be a 1 amp fuse that had blown in the fuse box that controlled the smart charging. The electrician told me that unlike alternators of old, you do not need a 12V feed to excite the alternator and if the fuse has blown, it will overcharge. Might be worth checking your fuse before anything else.
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