Jules wrote:
On Tue, 10 Feb 2009 02:08:47 +0000, Doctor Drivel wrote:
Why would a poor earth increase the voltage of an alternator?

I believe it messes up the voltage regulation if anything in the charge
circuit goes high-resistance, such that the regulators end up putting out
a higher voltage than they should.


Check on the battery type. If it is the Ford smart charge system then
the battery should be a silver cadmium battery and will charge at 15 or
more volts. The voltage is not only a function of the the smart charge
controller but also of ambient temperature.
I have this system on my Cmax and it was the subject of a recall where
the batteries were becoming discharged in cold weather and failing to
start especially the diesels.
If the OP has this system then it is vital that any replacement
batteries are of the silver cadmium type.
Another characteristic of the Smart Charge system is the delay in
reacting to a heavy load on the battery.
I notice that the heater blower gets considerably louder/faster tens of
seconds after pulling away with heavy loads such as lights and heated
front screen switched on.
On my other older car, the fan speeds up instantly after pulling away.

Blowing bulbs is obviously unacceptable so the vehicle should still be
checked under warranty.

Bob