High voltage output (16.8V) from Volvo Penta MD2020-A alternator

[MattS]

Getting 16.8V across the batteries with revs just above idle.

Want to check my initial assumption that this is likely a dodgy alternator (it may well be original so circa 25 years old), and best course of action is probably to replace the alternator?

Any of potential causes to investigate e.g. incorrectly wired that could cause same symptoms?

 

[Birdseye]

16.8v is too high assuming you have used a proper digi voltmeter and arent trying to read off the cheepo moving coil job that boat builders love to install. Dont see how the wiring can change itself from correct to wrong.

I had a similar issue some years back with a 2030.. I cant remember the full tec detail though I can remember that is was off Fowey - such is old age. Anyway, it required a new alternator and I had real trouble with engine heat and cheepo chinese alternators which fixed the diode with ordinary solder. It needed to be silver solder with a higher melting point because the ordinary stuff half melted giding a dry joint. 2 alternators later I bought one made in europe.

 

[LittleSister]

Failed regulator will (or at least can) result in excessive voltage. I had that very issue on an alternator.

In my case the regulator was mounted on the rear of my(Paris-Rhone) alternator so easily accessible, a replacement was readily available for a modest price (c£17 IIRC), and once obtained was fitted by me in about 20 minutes (including taking pics and drawing a diagram so I rewired it correctly). Problem immediately solved.

I don't know if all alternators would be likewise. You would likely need to identify the make & model of the alternator itself to obtain spares for it or replace it (at least to avoid paying the Volvo premium on someone else's parts).

Get it fixed a.s.a.p. or you may be replacing your fried batteries, too!

 

[MattS]

Thanks. Yes, voltage was measured across battery terminals using a digi meter, so pretty confident in the reading.
Have been offered a new Volvo Penta alternator for £175, hadn’t thought about just changing the regulator - will do some googling. Likely to just replace the whole thing so we know it’s all good, rather than risk delaying planned trip even further. Definitely don’t fancy trying our chances with new batteries and 16.8V charging!

 

[roaringgirl]

I second the suggestion of replacing the regulator.

 

[VicS]

Thanks. Yes, voltage was measured across battery terminals using a digi meter, so pretty confident in the reading.
Have been offered a new Volvo Penta alternator for £175, hadn’t thought about just changing the regulator - will do some googling. Likely to just replace the whole thing so we know it’s all good, rather than risk delaying planned trip even further. Definitely don’t fancy trying our chances with new batteries and 16.8V charging!

Some alternators are easier to work on than other but if your alternator is the standard one fitted to a MD2020A ITYWF that it has a combined regulator and brush assembly which is easy to change, Don't buy one at VP prices though !

Alternatively consider having the alternator overhauled by an Automotive Electrician ( Curd Bros in Tunbridge Wells have a good reputation)

 

[Alex_Blackwood]

Thanks. Yes, voltage was measured across battery terminals using a digi meter, so pretty confident in the reading.
Have been offered a new Volvo Penta alternator for £175, hadn’t thought about just changing the regulator - will do some googling. Likely to just replace the whole thing so we know it’s all good, rather than risk delaying planned trip even further. Definitely don’t fancy trying our chances with new batteries and 16.8V charging!

Fit new, have existing repaired, keep as spare or sell!

 

[MattS]

Thanks for the suggestions! We’ve managed to find a replacement alternator that we’re picking up today, so our plan is just to replace the whole thing so as to try and avoid having to completely cancel our trip! I’m hoping that we’ve understood correctly, and that replacing with a new alternator will replace both the alternator and the regulator - and hopefully give us peace of mind about the charging at least! Getting the old one renovated a good idea though as a spare.

Of course, it’s never that easy.. the water pump now needs replacing too! ?‍