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Is my Alternator kuput or something else

Fiat Ducato

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Recently been experienceing some issues when driving my 1997 1.9TD Fiat Ducato, where the battery light flickers on and off at times like accelerating up hills etc.


My first thought was it was my voltage sensing split charge relay causing the issues as they stay connected for a time after engine is switched off, also if I wish to charge my habitation battery with a mains charger the engine battery and hab battery become connected in parallel meaning I am charging both at the same time.


So I removed this relay and fitted with a standard split charge relay like the one off aandncaravans website.


However the problem is still happening but only at times, when it does happen my fridge is on 12V working and my habitation battery is charging fine. I only have one 90AH Leisure battery fitted


Is it just a case of alternator doing too much work and straining or is it had it, I read somewhere it could be the voltage regulator packed in with charging both batteries together on a mains charger. Used a 20A 5 stage connect and forget battery charger.


As always any comments, advice, and help is always welcome and will be RESPECTED




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I am no electrics expert and it may or may not be related but have you ensured your battery earth circuit is good, clean and tight connections and an adequate engine to chassis earth strap as some Ducatos are known to have an earth circuit issue, particularly with an earth strap that looks good but isn't?

Just add a second earth strap between engine and chassis to resolve this. A dodgy earth can cause all manner of strange effects?

Does it start OK and do any connections get overly warm when the engine turns over?


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It could be anything, slack drive belt, worn brushes, faulty regulator, bad connections and so on.


Any good auto electrics place should be able to find the fault in about 5 minutes.


Alternators have a hard time on motorhomes, running the fridge, charging two batteries etc. They do wear out.




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I had a similar problem with my x250 and it was difficult to find but it eventually got worse and the step & fridge stopped working and leisure battery stopped charging. Making it easier to find a fault as this pointed to a fault with the D+ signal the small wire from the alternator sends to excite these devices. Sods law I started the alternator end and stripped out all the loom tracing the wire before finding the fault below the ecu where it had rubbed against a tubular mounting bracket and was shorting out. Since then I found on the fiat Forum this is a common fault
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I tend to keep my vehicles a long time, and in over 50 years of motoring experience alternator faults have been few. In confirmation of the suggestions made by Hallii, the faults encountered have been slack drive belt, a winding fault, two faulty regulators and a few worn brushes.


In view of the fact that the symptoms appear when accelerating, may I suggest a worn or slack belt as the next suspect to be investigated.


It may be relevant to mention that my problem with a slack belt was with a retrofit alternator kit on a Land Rover many years ago. There was insufficient adjustment available to fully tighten the belt supplied. The problem only became apparent after about 40 minutes running with headlights on. As the belt warmed up, it stretched slightly and slipped more, warming further with the friction. The output fell away quite rapidly.









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Most older, none ECU controlled Alternators have two '12v' outputs, the first is the main charging output from the B+ terminal.

The second is a much smaller output, usually up to 2 amps, that is used to 'put out' the Ignition warning light, the D+.

The D+ output is also often used to drive the Split charge relay and trigger the Fridge, etc. as the 'signal' that the engine is running.


When an Alternator usually fails, such as burnt out regulator, melted coils or damaged rectifier, both outputs are lost.

If the Alternator isn't being driven fast enough, like when the Belt is slipping, the output can be so low it may not have enough power to extinguish the Ignition warning light or charge batteries.


As already mentioned above there can be a short or poor connection on the D+ circuit which means that the Ignition warning light may stay lit or flicker, but the main B+ charging output is fully available.



I would guess your problem is an issue on the D+ circuit.



To help diagnose where the problem lies, check the starter battery voltage at idle and again at fast idle.

If the output is a solid 14.4v (that is with the Fridge off) then the chances are you have a good Alternator and drive system.


Now repeat the readings with the Fridge on 12v and all the lights on in the habitation area.

Don't be surprised if, with the Fridge on, the voltage is as low as 13.0v on some manufacturers motorhomes. This is not abnormal and caused by the extra load creating a voltage drop.


I would guess, that aside from issues caused by 'poor Earths', you will find strong voltages at the Starter battery.



Note 1 : the above voltage values assume two perfect batteries. If one or both batteries is tired, it may distort the results. It is very important on an older vehicle to ensure the load on the Alternator isn't above it's limit, which can be quite low.


Note 2 : The 'Continous running' limit of an Alternator will be about 2/3 it's rated value which is a Peak rating not continuous running value.

I am guessing you have a 90amp Alternator, so about 60amps continuous running capability. Make sure the batteries are perfect, young and quality, they have a huge impact on alternator life.


Note 3 : Big Trucks that do long distance journeys have an overnight 'habitation area' behind the Drivers seat with Diesel powered Heater, Kettle, TV, etc. which in the last couple of years has often included a big Inverter to run it all.

As a result the Battery/Alternator load has risen massively but nothing else has kept pace.

The result has been numerous battery failures along with Alternator failures in an area when 5 years ago a truck Alternator failed through bearing issues at 250,000 miles. Now they fail from overload at low mileages

It has got so bad that Bosch have brought out a special Big Truck Alternator version that monitors it's own temperature and winds down the output if it starts getting hot from being overloaded. See :




What I am trying to say, is that battery quality is key to Alternator life and if the Alternator is goosed and you do have to replace it, fit one that meets the load of a modern motorhome.



Oh yes, and treat with caution any "battery magazine articles" that advocate extra/bigger batteries, etc. without any mention or concern for the Power unit/charger/Alternator load that results. It isn't just the Alternator that gets loaded up, some power controller/chargers won't cope with a bigger battery bank.

See our gallery of horrors here : http://www.aandncaravanservices.co.uk/add-a-second-battery.php




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Sorry I meant to mention it a couple of weeks ago but have been busy, we had our first Alternator failure on a vehicle for a while. Hopefully the message is getting through so seeing less overloads?


However, there might be evidence of a new potential Alternator issue on the horizon relating to battery upgrades and this might be a good place to mention it?

In June we had in a 2017 vehicle with a failed alternator that had been converted to Lithium and as Clive Mott's MMM battery article says "Liithium can be charged and discharged at much greater current".



A 100Ah Lithium will accept up to a 100amps charge, 2 x100Ah Lithiums may accept up to 200 amps.

Of course it's not going to stress a 140amp alternator (continuous charge rate is about 100amps, as 140 is just a short term 'peak' rating) that is already supplying 18amps to the Fridge, 15 amps to the Starter battery, 30amps just to run the vehicle ECU, Injectors, etc


Yes of course the Installer uprated the Alternator and all it's wiring to the Lithium pack, they knew what they were doing........................




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I was going to suggest a possible loose connection in the alternator D+ circuit.


I note that Allan has already made this suggestion


It is conceivable that such a loose connection would only become apparent when the engine moves in its mountings as the vehicle accelerates. If the connection to the D+ terminal is lost, the charge warning light may illuminate at reduced brightness as current will now flow through it and split charge and or fridge relay coils.



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Thank you everyone for all your comments and advice, and now I have a few pointers to get me started and to check.


I have just back from a kayaking trip which was about 70 miles round trip, and on the way there, I left the fridge off till I had travelled a few miles then switched it on. However the battery light was on and off most of the way, whether the fridge was on or off. However on the return journey I left the fridge off completely and the battery light only briefly come on once and went straight off again. But when I got back I notice that when I checked the habitation battery monitor it didn't show fully charged like it usually does after driving.


So I will check all the connections tomorrow and look at the D+ on the Alternator.


This van as a few bad habits or gremlins, weird irratic behaviour, I have a similar problem with the engine running hot, it stays at 90 degrees around town and B roads, but as soon as I speed up and put it in 5th gear especially on the motorway the temp goes up to 105/110 Degress and just sites there. Doesn't ever seem to any higher and temperature warning light never seems to come on. But we were planning a trip to a few countries in Europe during the summer holidays with the kids. But as most of the journey will be motorway driving I'm not sure I trust it, surely running an engine hot ter then it supposed to be for long periods can't be good for the engine/head etc.


So far I have replaced the radiator, temp sensors, removed the thermostat and checked it all works properly, which it does. The entire coolant system as been flushed through three times, twice with rad flush. It was flushed through thouroughly, I mean removing thermostat, removed and cleaned expansion tank, removed radiator and flushed that through separately. Same with the heater matrix system, removed both hoses and flushed right through. Loads of rusty coloured water flushed out each time.


I've checked vans are working correctly and they are. Also the mechanic tell me that he is fairly sure that my water is working ok as when he removed the return hose to the expansion tank it was pumping water through, a sign that the water pump is working as it should, he asked me if when I turn the heat setting to max hot, does it blow hot air, which it does as this is another tell tale sign your water pump is not working, along with no noise or water leaking from water pump area.


So now left wondering what to do next, thought about fitting a manual overide switch on the dash for the fans when it starts to run hot. Or head gasket? Kids will be disappointed if we can't make it through the blinking van.


anyway enough of my sad stories and problems.


Thank all





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I had a similar problem on my Ducato based van. I traced the fault to a bad connection caused by a clip-on 'scotch lock' connector. This was on the feed wire to the split charge relay. The connector had virtually cut through the lead to the 'ignition' light.
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