1998 fiat ducato Hobby 750 electrical mystery

[lovingliving]

We have just done a 4000km trip through France Italy and Spain and have a mysterious electrical problem. Hoping someone might point us in the right direction to solve it. Before leaving home if the van was left a few days the cab battery would be flat. We purchased a new battery but still had the same problem. The alternator light does not come on EVEN on start up. The on board gauge for the cab battery shows zero charge unless plugged into mains for a few hours when it will show fully charged. We have not had any problems starting the van whilst away. The leisure batteries have been fine (we have solar as well). The cab battery shows around 12v on a multimeter. We have not used the fridge on battery and have avoided driving at night so as not to use headlights etc. Question is is this likely to be the alternator? Could it be the alternator warning bulb and if so how do I get to it to check? Tried to remove the dashboard but can’t get in because of the speedo cable, or is it likely to be something else entirely? Don’t want to pay for a new alternator if it’s not going to solve the problem. Over to you any advice gratefully received. Thanks

 

[autorouter]

It's easy to see if the alternator is working if you have a multimeter. The cab battery should be about 12.0 to 12.6V when the engine is stopped, and your multimeter reading confirms this.

When the engine is running, the voltage should rise to over 13.0V, ideally to about 14.5V. This shows that the alternator is charging the cab battery. If the voltage doesn't rise then you have an alternator problem. It could be a broken alternator drive belt, or a faulty earth strap, but if the alternator is spinning but not producing power, chances are it's faulty.

 

[lovingliving]

Thanks for that. Just gone out to start it to test after standing for three days and it is completely flat no charge in the battery at all. The leisure batteries are still fully charged. Surely that can’t be the alternator? I have checked and nothing was left on.

 

[GeoffnDee]

The Alternator could have faulty Diodes allowing it to drain the battery

 

[lovingliving]

Is there a way I can test for this?

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[psyfried]

hi i had a car that used to have the same pronlem turned out to br the altanator light on the
dash was not workimg the bulb had blowen was told the light on the dash needs to come
on to activate the alternator when you start up

 

[GeoffnDee]

Is there a way I can test for this?

You can use your multi-meter - Switch the voltmeter to low setting on AC voltage scale - With the engine running ,put the probes on battery terminals - The volt meter should read zero AC volts - if there is any amount of AC voltage it indicates a bad diode .
You may be able to replace just the diode pack but a replacement alternator (after having it confirmed as faulty) may be a better way to go.
Although the charge light bulb being blown can effect charging I would not expect it to cause battery drain (your starter battery may also have been damaged with the amount of discharge that it has had)

 

[lovingliving]

Hope not because it is brand new I’ll have a look thanks. Does anyone know how to disconnect the Speedo cable so that I can check the bulb as well?

 

[autorouter]

It's looking very much as if the alternator is the problem. As a final check, if you need one, you could charge up the starter battery and see if it discharges - no doubt it will. Then you could disconnect the alternator feed, and see if it still discharges. If it doesn't then the alternator is the problem. If it still discharges, you can then look for the cause, but at least you will know.

By the way, don't try starting the engine with the alternator feed disconnected, it can cause all kinds of problems.

 

[GeoffnDee]

If you are able to confirm which wire (normally the thin one)) on the rear of the alternator is connected to the warning bulb circuit disconnect it from the rear of the alternator and earth it out ,with the ignition on , if the bulb is ok. it should light up.

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