Volvo Penta D6 alternator problem

[mcanderson]

One of my alternators is playing up. When I start the engine the voltage drops as expected and then returns to just over 14v. So far so good. After 10-15 secs it drops to the battery voltage of 12.6ish and I get an EVC alarm for low voltage, so nothing from the alternator. If I increase the engine RPM to 1400 the alternator springs back into life and the voltage gauge reads just over 14v and the alarm goes out. If I return the engine to idle the alternator keeps working fine.

To me and an aircraft engineer friend this sounds like a regulator issue. But I am happy to be corrected.

Any suggestions for testing would be appreciated.

Does anyone know if the regulator is internal or external to the standard VP alternator?

Heading to the boat this weekend armed with the multimeter!

 

[Portofino]

Insufficient belt tension
Ck adjustment 1st
2nd ck corroded connections @ the rear / has it been drenched a lot ?

 

[mcanderson]

Thanks, I will do. That forms part of my prestart checks, but it never hurts to check.

 

[jimmy_the_builder]

The alternator is made by Mitsubishi for Volvo, unfortunately the regulator is internal so if it is the regulator, you have to replace the whole unit. From memory they are about £700 from Volvo, and maybe a bit more than half that if you buy the Mitsubishi part instead (that's what I did).

 

[volvopaul]

I have a fully reconditioned unit here if you need it , price via PM .

 

[robrennie]

Just a thought.
If you have a twin engine installation, are you sure that you do not have the batteries connected - some boats have a switch that allows them to go into parallel for engine starting.
Having two batteries and two alternators can be confusing for the sensing part of the alternator.
Best of luck

 

[mcanderson]

I have a fully reconditioned unit here if you need it , price via PM .

VP- any other fault finding I can do?

 

[mcanderson]

The alternator is made by Mitsubishi for Volvo, unfortunately the regulator is internal so if it is the regulator, you have to replace the whole unit. From memory they are about £700 from Volvo, and maybe a bit more than half that if you buy the Mitsubishi part instead (that's what I did).

Thanks. Top tip!

 

[inception]

when the regulator dies, you normally don't get any charge. The regulator is nothing but some diodes so when one is faulty it will affect the others... so I doubt if it's faulty regulator - most likely a loose connection or corroded connection.

 

[mcanderson]

Inception - thanks. I will check the back of the alternator and trace the wiring. The engine room is very dry and there are no signs of corrosion on any other part of the engine affected.

I will be on my boat this weekend so it looks like I will be sending some quality time with my multimeter.

 

[Pawseidon]

I know this thread is two years old but I have a VP D6-370 with exactly the same symptoms.
mcanderson, did you ever find the cause?

 

[mcanderson]

Pawseidon - in short no I haven't solved this as I have learnt to live with it. My alternator comes on line after start when I increase the revs 'in neutral' to 1300. I do this soon after start, allowing a couple of minutes for the oil to circulate. It works everytime and as there is generally something of a higher priority to spend money on on the boat it has remained on my list of things to do. That list has grown this year due to the lack of ability to get to my boat.

I look forward to getting flamed for not fixing this sooner.

 

[vas]

without knowing how your boat is setup, and assuming all connections and tensions are fine, could it possibly be the exciter circuit playing up? was another similar thread on PBO (I think!) a few weeks ago that also helped me solve the issue I had on mine

 

[Portofino]

without knowing how your boat is setup, and assuming all connections and tensions are fine, could it possibly be the exciter circuit playing up? was another similar thread on PBO (I think!) a few weeks ago that also helped me solve the issue I had on mine

Yes but VP s are sealed units .I do not think it’s just ( regulator ) a bolt on part .

Left of field worth checking out is its battery it’s supposed to charge .If it’s got a cell down after starting its voltage may drop below the excitation criteria .The ECU detects this and throws a code / alarm .
A few revs later the 1400 or what ever issue disappears as the battery albeit weak manages to recover its voltage to rise enough within the parameters.


In the automotive world you can send them away for rebuilds , commutator clean , replace , the voltage regulator which is just a set of diodes replaced and the pulley bearing replaced .

My money is on a dousing albeit inadvertently because it’s under the path of water drips when checking the strainer .Corrosion somewhere .
I made a splash guard on my KAD 300s , waxoiled the thing and regularly lubed the bearing .Regularly cleaned up the contacts at the back - rubbed them up with Emery paper and reconnected etc . Also if you over tighten the belt ( easily done ) that shortens the bearing ,If it’s that tightened ( and corroded / poor lube ) up it may be stiff at start until a few motions or the 1400rpm to free up and spin up to voltage threshold hence the code / alarm or light ?

Just poor packaging with an inevitability.
Having said that because I recognised the potential problem and fitted the splash guard + other interventions mentioned mine lasted the nine years of my tenure .

At boat shows the second place I look is the ER @ the instal . Looking for the “ what ifs “
The first the hull deadrise ......moot point on here