Weird Battery Voltage

[SwissBob]

Experiencing some strange behaviour with the engine battery on our 2002 Fuat Ducato 2.8 JTD.

I noticed on the Victron dc-dc charge the input voltage was only 12.2v with the engine running. Got out the trusty meter and sure enough only 12.2v across the terminals. The battery warning light does not come on.

Had the alternator removed and bench tested at a Bosch service center. All normal, 14.2v and 135amp output, regulator ok, they checked the battery warning light is functioning ok.

They put it back on and still only 12.2v across the terminals.

As we had to get the ferry back to France we left it at that and are currently limping home, charging up overnight and just doing 2 to 3 hours at a time. No issues starting but when the voltage drops we get black smoke when accelerating hence stopping to recharge often. Full recharge takes it up to 13.6v without the engine running.

Anyone had this or similar? One thought is the battery (4 years old) is knackered but in that case why isn't the warning light coming on?

Baffled.

 

[bigtwin]

Polished alternator belt?

Ian

 

[RogerIvy]

Is yours a smart alternator?

We have noticed on a few Motorhomes with smart alternators that the voltage can go down to 12.2
TBH this is not the rule, probably only seen a handful where the voltage goes that low.

When they bench tested and assuming you have a smart alternator they would not have had the same setup as you (ie shunt and computer system to decide when the alternator should work or sleep). It’s worth asking about that.

 

[SwissBob]

Polished alternator belt?

Ian

No, replaced when they stuck it back on.

 

[SwissBob]

Is yours a smart alternator?

We have noticed on a few Motorhomes with smart alternators that the voltage can go down to 12.2
TBH this is not the rule, probably only seen a handful where the voltage goes that low.

When they bench tested and assuming you have a smart alternator they would not have had the same setup as you (ie shunt and computer system to decide when the alternator should work or sleep). It’s worth asking about that.

Original 2002 alternator so not smart at all

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[RogerIvy]

Original 2002 alternator so not smart at all

Ah yes you did say 2002 in your original post. My bad.

For an “older” vehicle 12.2 is pretty low. What happens if you try a different battery?

And for the record I think smart alternators are the dumbest thing on a motorhome

 

[SwissBob]

Ah yes you did say 2002 in your original post. My bad.

For an “older” vehicle 12.2 is pretty low. What happens if you try a different battery?

That's the next step once (if) we get home .

 

[DBK]

I would disconnect the B2B and see if it makes any difference. At the moment with it connected it adds too many variables so you need to check the original charging system is still working. This is isn't a solution but will help narrow down the fault.

 

[SwissBob]

I would disconnect the B2B and see if it makes any difference. At the moment with it connected it adds too many variables so you need to check the original charging system is still working.

Yes, I thought that too. Disconnected before the ferry then 2 hour drive to where we are now. No change.

 

[RogerIvy]

Yes, I thought that too. Disconnected before the ferry then 2 hour drive to where we are now. No change.

BTW if you need to stop the DC-DC to test things it’s really easy to do in the app. No need to actually disconnect.

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[DBK]

Yes, I thought that too. Disconnected before the ferry then 2 hour drive to where we are now. No change.

Then if the alternator is working it must be something between the alternator and battery. There's probably a fuse, possibly on the battery positive terminal.

 

[bigtwin]

Then if the alternator is working it must be something between the alternator and battery. There's probably a fuse, possibly on the battery positive terminal.

Sounds like it, a high resistance joint somewhere.

Ian

 

[SwissBob]

BTW if you need to stop the DC-DC to test things it’s really easy to do in the app. No need to actually disconnect.

Then if the alternator is working it must be something between the alternator and battery. There's probably a fuse, possibly on the battery positive terminal.

There is a red thing on the +ve terminal that could indeed be a fuse. In the morning I'll take a closer look. Red one looks like 50 amps. Also two others. Not sure about them.

 

[bigtwin]

There is a red thing on the +ve terminal that could indeed be a fuse. In the morning I'll take a closer look. Red one looks like 50 amps. Also two others. Not sure about them.



View attachment 979570

I’d have thought that the alternator connection is more likely associated with the large fuse on the RHS.

Ian

 

[DandG5515]

Dodgy earth strap try a jump lead from engine to chassis or engine to negative terminal? See if it makes a difference.

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[GeoffnDee]

I do not Know if your Ducato (X244 ? ) is the same as the X250 but that series often uses the main battery connection at the starter motor as an alternator power supply back to the starter battery and it could be worth checking this connection point at the starter for tightness etc. (If yours is the same)
As suggested the engine to body earth lead could be faulty and can be checked as described above.

 

[autorouter]

There is a red thing on the +ve terminal that could indeed be a fuse. In the morning I'll take a closer look. Red one looks like 50 amps. Also two others. Not sure about them.

It's a battery terminal distribution block, something like this one.
https://www.12voltplanet.co.uk/battery-distribution-fuse-box.html
The red one is a link fuse. Midi size. like these

Midi Link Fuses

Midi link fuses used for protecting larger current circuits in automotive, marine and leisure applications. Available in current ratings from 30A to 150A.

www.12voltplanet.co.uk

 

[SwissBob]

Dodgy earth strap try a jump lead from engine to chassis or engine to negative terminal? See if it makes a difference.

Fixed. This was the problem. Permanent fix will be done when we get home.

Thanks everyone for all the suggestions, it's been a great help.

 

[Peregrinator]

Try to get someone who actually understands the way smart alternators work, also test Earth strap and look at the belt.

 

[Reevsie]

Had a similar problem with my engine battery. When the engine was running it was only putting in 12v to the engine battery. Took it to a Fait dealer who said it was the alternator and would need a new one.
Before they replaced it the found a large fuse had gone. Think it was a 100A fuse. They replaced it and it started to charge okay. at 14.4 V
Not sure where the fuse was, they just told me the located a large fuse and it had blown.
Cost me £102 in labour and £4 for a fuse.
Better than a new alternate.

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