Charging Problem

[Marcus_phillips]

Okay, my wife's Ford Focus lit up like a xmas tree last week (no jokes please) now I know this is a low battery fault. Now to cut a long story short I have wired a digital ammeter inside the car to see the voltages coming from the alternator. At Idle just over 13v at 2500rpm and over 13.9v, now for the problem, when I use the side lights it drops by approx. 0.2v, but when I put the heater fan onto number 1 the voltmeter shows 12.3v, in effect the alternator not charging. There is no light on on the dash and when I turn the heater off after around 10 secs it starts to charge again (13.9v). Any ideas? sounds like a dicky alternator but not sure any help.

[jeebowhite]

Alternator is certainly suspicious, however the heater is a high output item. IIRC, putting heat on with the heated windscreens the car should be running at around 13v at least....