VP Alternator issue

[mcanderson]

So I replaced an alternator that wouldn’t produce an output above 12.5 V unless the engine was above 1400 RPM and then it worked fine even when revs dropped below 1400RPM. Consensus was regulator so I replaced the whole alternator.

New alternator fitted and at idle at the dock produced 13.3v. Happy days, but I have just gone for the first trip and it again dropped to 12.5 ish and low voltage warning on the edc. This was regardless of revs.
Any ideas?

 

[Mr Googler]

Do you have the 4 vp warning lights display….does the alternator warning light illuminate?

Theres something about if the little bulb blows or gives an intermittent issue…..the alternator won’t get excited.

 

[BruceK]

Split charger? Does your yellow wire on the back extend to the split charger or batteries?

Also follow the D+ wire. I am not sure what boat engine setup you have but it leads to the warning lamp control box and needs the alternator light bulb to work to excite. Check bulb is functioning and wire continuity.


edit. Pipped by the car park attendant. The shame!

 

[mcanderson]

Do you have the 4 vp warning lights display….does the alternator warning light illuminate?

Theres something about if the little bulb blows or gives an intermittent issue…..the alternator won’t get excited.

No lights. EVC-B displays in the bottom of the Tachometer only.

 

[mcanderson]

Split charger? Does your yellow wire on the back extend to the split charger or batteries?

Also follow the D+ wire. I am not sure what boat engine setup you have but it leads to the warning lamp control box and needs the alternator light bulb to work to excite. Check bulb is functioning and wire continuity.


edit. Pipped by the car park attendant. The shame!

Yes there is a yellow wire. I will check where it runs to. It runs into the wire harness for the engine (D6-330a).

 

[Portofino]

It’s not a genuine VP part if I recall ?
Maybe there’s ( the genuine ) has a unique regulator , or at least a EDC communicator able one ?

 

[mcanderson]

It is very same model. The one I took off had Mitsubishi and the model and so does the one it fitted. VP source from Mitsubishi.

 

[Portofino]

Have you opened up , took the covers off the regulator bit at the back .
Pic would be nice of both regulator gubbins .
If it’s identically fitted wire for wire seemingly perfect switch out then start investigating differences ……if any ?

Bentley forums are full of guys buying a Bosch VAG alternators ( same engine as Audi W12 / VW W12 phaeton ) at 1/2 price coming unstuck with similar . That’s all .
Something to do with the electrotwackery at various ECU ends .….has to be just so apparently.

 

[mcanderson]

Right in the wiring diagram there is this sense cable running to some sort of switch to changing the charging voltage. Any idea what one of these looks like?

 

[Portofino]

Your batteries are knackered .

 

[Montemar]

We have the same alternator on our Broom 33.
The yellow wire goes to the domestic batteries so they get fully charged. B+ goes to the starter battery so gets charged slightly less fully but still enough to function properly.
The split diodes are in the plastic casing on the back of the alternator.

 

[mcanderson]

Thanks for trying. I don’t have a yellow wire running to my batteries. Nor when I removed the old alternator did I see a case with any wires running to it.

 

[Portofino]

Are we going to see pics of the regulators , or more importantly the insides of the little black boxes .
We get the main body , brackets etc are identical to Mitsubishi . No engine marine manufacturer or car make alternators, they are all off the shelf .But crucially the regulator could be tuned to that particular application.

Might not be , so genetic works .But if it is , it has to be compatible.

Reason why in the car / auto world a perfectly fitting cheaper spare fits a Bentley from a lesser modal VW and throws up more lights than Hamleys at Christmas is because inside the little black box the gubbins are tuned into a different battery size .
Eg a 140 Ah + 80 Ah to a80 Ah and60 Ah .

Duff batt bank is another reason why you through the light in the first place , so the original A might be perfect .
Did you test said batt(s) ?
On the previous thread you never said exactly why you bought another A iirc ? How you arrived at the conclusion it needed replacing iirc ?

You have wired it up correctly back to back that’s not the issue .

 

[Montemar]

The casing looks like the back of the alternator. The split diodes are inside it.