Alternator Issue on 2.8 JTD A Class

[PhilG]

I need to find the Alternator fuse on my A Class Euramobil 2.8 JTD to see if its the cause of my battery light staying on.

Alternator is newly refurbed, and has been fine for 700 miles, all I can find is that the fuse should be on top of the battery, but on the A class is seems to be elsewhere.

All help appreciated.

 

[Carolyn and Kev]

Stupid question....Belt tight?
Not sure why it should be a fuse bud? Normally the light is ON due to a circuit fault either with the alternator being at fault or the wiring from it. The Alternator needs to see the light to make a circuit. Ignition on ..the circuit is made through the bulb back to earth so light is on. When the alternator turns ...it goes off indicating a full circuit . If the light stops on...normally the alternator regulator is at fault. You state that the alternator has been refurbished? Ideally a s/exchange would be the least way forward to be honest. That way you have a full warranty with the alternator.
That aside..wiring need to be checked and can only be done with a Multi meter .

Kev

 

[PhilG]

Stupid question....Belt tight?
Not sure why it should be a fuse bud? Normally the light is ON due to a circuit fault either with the alternator being at fault or the wiring from it. The Alternator needs to see the light to make a circuit. Ignition on ..the circuit is made through the bulb back to earth so light is on. When the alternator turns ...it goes off indicating a full circuit . If the light stops on...normally the alternator regulator is at fault. You state that the alternator has been refurbished? Ideally a s/exchange would be the least way forward to be honest. That way you have a full warranty with the alternator.
That aside..wiring need to be checked and can only be done with a Multi meter .

Kev

Belt is fine, no resistance from alternator so tickover is high. It probably isnt the fuse, but i want to check / change it before i pull the alternator off again as its a PITA , cant get directly onto the alternator to check that . What is a service exchange alternator if its not a refurbished one. ? Its just one they did earlier , I got my original back and I have 12 months warranty on it.

So what you are saying , is that if the light is on , there is a circuit and the fuse must be OK ? Good if so , so i dont need to look.

 

[Baggydave]

We have same engine & while changing the oil pressure sensor i blew a heavy fuse atop the battery By shorting on the alternator.
it was a Flat strip one & bolted down. Cant remember the ampage But it was pretty high.
point is our ignition light Stayed on Till I replaced the obviously blown fuse. All fine since.

 

[Carolyn and Kev]

Belt is fine, no resistance from alternator so tickover is high. It probably isnt the fuse, but i want to check / change it before i pull the alternator off again as its a PITA , cant get directly onto the alternator to check that . What is a service exchange alternator if its not a refurbished one. ? Its just one they did earlier , I got my original back and I have 12 months warranty on it.

So what you are saying , is that if the light is on , there is a circuit and the fuse must be OK ? Good if so , so i dont need to look.

No ....what I am saying is that the circuit from the battery through the ignition switch and the alternator to the light and down to earth is ok. The Alternator when its charging will see the light then...switch it off in order to charge the battery, that is a simplified view of how it works. The light on whilst running..means a failure with the charging circuit . It can be either the wiring or the alternator. If the System has worked for the last few months..something has given up and bought on the light. Simple check is to put your multimeter/volt meter on to 20 volts and run the engine up. Check before the engine is running at the battery for ease ..then check when in motion(engine running) . If there is a difference ..check the wiring first then return back to the regulator on the alternator.
Refurbished is a term used by some...not all is replaced. Service exchange is yours for a completely rebuilt one and tested on a dynamometer for Alternator out put . There is a difference.

Kev

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[68c]

Most bulb type charge warning lights use a simple idea. When the engine is stopped and the ignition is turned on battery voltage at around 12.5volts is fed to the bulb, it finds its earth through the alternator D+ terminal. When the engine starts the alternator outputs through the D+ terminal at around 14 volts. The battery voltage quickly rises to near the 14 v so 14v is now applied to both sides of the bulb, it goes out. You need to find out if there is short between the bulb and the D+ terminal, or if there is no 14v coming from the D+ terminal. If you have van with a split charge relay, which is controlled by the D+ output, neither your leisure battery or your fridge will work.

 

[68c]

To correct my last point in my post above, I should have said 'if there is no output from D+ the leisure battery will not charge and the fridge will not work on 12v while driving.'