Ford Mondeo 2.0 TDCi Battery light on constant

[steski65]

The battery light on my 04 2.0 TDCi comes on constantly after about 20 secs, i noticed that my front and rear window heaters went off when the battery light came on, the car stated ok each time i tried until after a week my battery died. I'm thinking it's the alternator but does anyone else have any other ideas

 

[Spark123]

The alternator seems like the most likely cause.

 

[wotan]

Diode pack in the alternator has failed, bet your rev counter is not working either.

Wotan

 

[Peter.N.]

Some equipment requires more than 12 volts to operate, so if the alternator is not working that is probably responsible for the other failures.

 

[wotan]

What equipment on a car, takes more than 12 volts to operate.
I know HID lights run at high voltage, but the inital input is still only 12 volts.

Wotan

 

[Stivino]

It's not that they need more than 12V, it's that they don't work unless the alternator is charging. i.e. heated rear screens and other high draw items.

 

[Peter.N.]

Stivino

Is not access to the heavy load equipment switched on by the presence of a charging voltage across the battery supply? If not, how is it switched?

 

[Stivino]

I don't know exactly because I'm not an auto spark. I'll try to explain to you how it was explained to me. In the same as the charge light on the dash goes out; voltage from the diode pack and the voltage regulator are fed to the ign light, via the ign switch. As long as both sides of the light have equal positive voltage, the light won't come on, i.e. the system is working ok.
The same system is used to control a relay, which controls the high draw stuff.
Maybe not the most technical description, but that's how I recall it. I'm sure someone will be able to explain it better.

 

[wotan]

Stivino

Is not access to the heavy load equipment switched on by the presence of a charging voltage across the battery supply? If not, how is it switched?

Charging voltage across the battery is necessary but, heavy draw items are switched via relays, if the battery is not being charged then it will run down faster, the voltage would be reached where the relays 'drop out' and the heavy draw item will be disconnected, when this happens things stop working.

The diode pack in the alternator converts the three phase electricity produced, into DC, it should flow into the battery ie (charging).
The control of this charging current is controlled via the exitation voltage supplied to the alternators rotor, by a battery voltage sensor, if the voltage drops...more power is sent to the alternator rotor, to increase the output of the alternator, it's a balanced system.
voltage regulation and rectification are all usually contained within the alternator.
It is the stator that generates the output (3 phase) dependant on the voltage supplied to the rotor (moving bit)
the three phase output is rectified into DC and is fed to the battery, when the diode pack fails, it usually allows current from the battery to flow in the opposite direction, or not at all.

Wotan

 

[Peter.N.]

OK, I am familier with that but is it not the increase in voltage that triggers the relays? or is there a connection to the exciter terminal that tells it when the alternator is charging? I assumed, rightly or wrongly that there was a voltage sensing circuit that switched the relays.

Peter

 

[wotan]

I suspect heavy current draw items are inhibited, (via relays) that sense when the car is running, and these items are fed by a master relay.

Wotan

 

[Peter.N.]

Yes, but my question is how do they sense when the car is running?

Peter

 

[wotan]

Yes, but my question is how do they sense when the car is running?

Peter

They must receive a voltage from somewhere, and if that voltage is sufficient then they will operate.
As I am not an auto electrician perhaps someone who is would care to give a definative answer?

Wotan

 

[Peter.N.]

I would suspect that there is a voltage sensing circuit that detects when the voltage exceeds say 13 volts which was what I was suggesting in my first post but someone seemed to disagree, so I am just trying to find out exactly how it does work. I have been in electronics all my working life as a TV engineer but auto electrics have now turned into something completely different.

Peter

 

[steski65]

Diode pack in the alternator has failed, bet your rev counter is not working either.

Wotan

Thanks for your reply, is the diode pack incorperated within the Alternator, i have received some quotes for reconditioned ones and need to know if the pack is within the alternator or an additional extra ?