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Alternator faulty?


Dez

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Hello.

 

Quick overview of my problem... On a 2010 Fiat Ducat 2.3 Devon Aztec

 

Engine battery died from lack of use (vehicle stored). Used the onboard charger (switched from leisure to engine) and left charging overnight. Checked battery next day - it was hot and bubbling - knackered battery !!! New battery installed. Now starts okay but the battery light comes on and the engine revs higher at idle. Suspect the alternator is faulty? I have used a voltage reader and attached to battery. There appears to be no charge when engine running as it remains around 12 amps and doesn't increase.

 

Could frying the battery onboard done something nasty? Not sure how I can determine if the alternator is actually at fault?

 

Please - any tips appreciated on how I start troubleshooting - spent all night awake worrying about it :/

 

Thank you. P.S. I have limited knowledge of what I can use the multi-meter for :/

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Dez,

 

I am unable to think of a reason why cooking the battery, would damage the alternator, unless the charger was also faulty.

 

Given the cost of replacing an alternator, it is probably worth checking other items first.

 

The 12 amps (I think you mean volts.) that you mention for the new starter battery is too low and that it needs a charge. If charging via the on board charger, a cautious approach would be to try the charger on the habitation battery first. Check the voltage across the habitation battery, and abort the procedure if it rises above 14.5V.

 

A brief explanation of the traditional alternator (battery) warning light circuit. With the engine stationary, a small current flows from the battery via the ignition switch, through the warning light, and to the alternator D+ terminal. From the D+ terminal the current flows through the alternator rotor (field) via carbon brushes to chassis. This is what normally lights the warning lamp. With the engine running the small current through the rotor allows the alternator to start generating, and in doing so supplies itself via the regulator. When the voltage at the D+ terminal is the same as at the battery there will be no voltage across the indicator light, so it goes out.

(On modern vehicles the ECU controls the alternator. I do not know if that applies to your vehicle.)

 

The permanently lit warning light does suggest a faulty alternator. However there are other faults that can give the same symptoms. Some MH electrical systems (not CBE) use the 12V from the D+ terminal to operate split charge and fridge relays. A short circuit to chassis on this wiring will stop the alternator generating. Likewise I have seen reports of similar faults in the base vehicle wiring caused by abrasion near the LH? headlamp. Perhaps Nick Fisher, or Allan (aandncaravanservices) may be able to elaborate on this.

 

Is it possible that your alternator has been overloaded by trying to recharge starter and habitation batteries which were failing?

 

Mechanical faults could be the alternator drive belt, either slack or failed. (Fairly easy to check.) Worn or sticking alternator brushes are more difficult to confirm. With the battery negative disconnected for safety, if possible disconnect the D+ wire and check that there is a circuit to chassis through the alternator brushes and rotor. I would expect a few Ohms on this path. Access may be difficult.

 

As you do not claim to be electrically competant, you may wish using the services of an automotive electrician.

 

Alan

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Sorry, yes meant 12v not amps. Will get under the van and check all cables. Is there a way to test the output of an alternator without having to take it out? I was thinking - set multimeter to 20v, connect the red to the alternator (live output) and black to chassis? Will that give me a reading?
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Hello,

 

Before you do anything else!

 

With the engine switched off.

 

Locate the engine lifting eye on the left hand side of the engine, towards the rear. Locate the threaded stud at the top right side of the front grille; this is the jump start earth point.

 

Locate a jump lead (you only need half of a pair for this) and attach one end to the lifting eye and the other to the earth point making sure that any excess jump lead cannot get trapped in fans etc.

 

Start the engine and see whether the voltage recorded between the earth and the positive jump terminal under a little flap by the fuse box is higher than previously and whether the idle speed is still rising or at the normal level.

 

If it is no different, you probably have an alternator problem.

If it is much better, you have an earth problem.

 

I have written many articles about new or improved earth straps on this site so you should be able to find the help you need or someone will come along who knows better than i do how to find such things.

 

The idle speed increases because the engine ECU is not getting sufficient power or earth and it tries to compensate by raising the idle speed. It assumes it has to because of a poor charging circuit because it knows no better but in 19 cases out of 20 it is a poor earth that is upsetting things.

 

N

 

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Lots of useful advice, especially the earth test.

 

Check all battery connections are correctly made including the quick release engine battery negative, and its cable to the body earthing point. Examine the fuse carrier that mounts on the positive post ensuring all fuses are making good contact.

 

The alternator control, D+ signal and indicator light is quite different on the Ducato compared with the older systems. The body computer controls the alternator field current and thus the voltage. It samples engine revs and alternator voltage and controls as necessary. If the voltage is above a set level it switched off the charge light, if below it will increase revs to try to compensate and if this fails will illuminate the light.

The cables to the alternator and starter are common and connect to the battery via a CAL4, grey, fuse mounted with the fuse array on the battery positive post. You will see the alternator voltage here. The fact that the engine starts and other systems function suggest that all fuses are OK.

 

The body computer generates a simulated D+, alternator charging, that is available via an optional set of sockets mounted in the drivers B pillar, the motor home electrical system may use this, alternatively it may just use a key on signal.

 

With 12v on the battery it does suggest the alternator is faulty. As a 'grasping at straws' measure disconnect all batteries at the negative post to ensure there is no power to the van electronics. Leave for half an hour or so and reconnect, this will reset the body computer and may resolve the problem.

 

If, after all the tests, there is no alternator generated voltage of about 14.2 volts, it can only be the alternator or body computer, perhaps it was caused by excessive voltage generated by the charging system on a faulty battery.

If the engine battery has been failing for some time perhaps the excessive charging has caused damage.

 

Mike

 

 

 

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My Ducato had the same problem

Calked RAC and the guy said needs new alternator

Thanked him then googled the problem

Googleanswer more chance of worn brushes was the result even a youtube video showing the problem and how to fit a new brush pack

Ordred brush pack off ebay and fitted to van alternator in situe without any issues,couple of nuts a few screws job done

Cost about £12 and took about 90 mins

Ray

 

 

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