Volvo Penta charging problem.

[Mike_Cornwall]

Hi all, I’m pulling my hair out. I have twin Volvo Pentas. Stbd runs and maintains 13.5 v. Port runs initially at 11.5v and gradually drops over an hour or two to 10v. All batteries are new and charge fine on Shore Power or Generator. New belts and tensioned correctly.
With engine shut down I get battery voltage at alternator terminals which suggests to me cables are fine.
So, I remove the alternator and off to shop to buy replacement….. shop bench tests my suspect alternator and it’s kicking out 14v.
Anyone suffered from something similar? Thanks in advance

 

[SC35]

Start with a multimeter ... test the voltage output at the alternator end while engine running first.

If 14v at the alternator, work your way back along the cabling and test the voltage across any inline components / junctions to try and find the point at which 14v becomes 11v at the batteries.
The cables might be fine in terms of being connected, but engine off is the "hardly any amps flowing" case.
A poor ground or dodgy connection somewhere would mean that as soon as any current starts to flow, the voltage will drop.
(check that the voltage across the batteries really is 11v).

If 11v at the alternator, double check the (other) exciter wire from the key switch to it.
It fires up the voltage regulator, which if not active, you'll see a low voltage everywhere.

 

[Montemar]

Corrosion of cabling and/or connectors

 

[Mike_Cornwall]

Start with a multimeter ... test the voltage output at the alternator end while engine running first.

If 14v at the alternator, work your way back along the cabling and test the voltage across any inline components / junctions to try and find the point at which 14v becomes 11v at the batteries.
The cables might be fine in terms of being connected, but engine off is the "hardly any amps flowing" case.
A poor ground or dodgy connection somewhere would mean that as soon as any current starts to flow, the voltage will drop.
(check that the voltage across the batteries really is 11v).

If 11v at the alternator, double check the (other) exciter wire from the key switch to it.
It fires up the voltage regulator, which if not active, you'll see a low voltage everywhere.

Thanks for the info. I’ll give it a go

 

[gery w]

Depends on what engines and the setup, ie battery sensing or machine sensing?
On the back of the alternator is there a yellow wire that either goes back to a battery positive or loops to the b+ terminal at the alternator?
Check for high resistance contacts on the sensing wire as this will affect the alternator output.

 

[Mike_Cornwall]

Depends on what engines and the setup, ie battery sensing or machine sensing?
On the back of the alternator is there a yellow wire that either goes back to a battery positive or loops to the b+ terminal at the alternator?
Check for high resistance contacts on the sensing wire as this will affect the alternator output.

Volvo Penta kad44s. Back of alternator there is a short yellow wire

Depends on what engines and the setup, ie battery sensing or machine sensing?
On the back of the alternator is there a yellow wire that either goes back to a battery positive or loops to the b+ terminal at the alternator?
Check for high resistance contacts on the sensing wire as this will affect the alternator output.

kad 44s. Back of alternator has a yellow wire that loops onto B+ terminal.

 

[gery w]

Volvo Penta kad44s. Back of alternator there is a short yellow wire

kad 44s. Back of alternator has a yellow wire that loops onto B+ terminal.

Ok so it regulates the alternator output from the b+ terminal of the alternator.
Make sure all terminals are spotless and that alternator has a good ground, from memory thes are insulated return and the alternator relies solely on the black wire for ground.
When you a showing the 10v on inst panel measur output at rear of alternator, fault could simply be a faulty voltmeter.