Alternator alarm sounds at idle

[landonshaw]

I have a MD2040D Volvo Pena. Had alternator problems and had one rebuilt. We have a two alternator system. Prior to the alternate alternator being rebuilt, when at idle the alarm did not sound. Now it sounds periodically. Very annoying when trying to anchor or Moore while listening to what is happening up on the bow. It never did it before. Suggestions?


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[Emmalina]

Apart from the obvious belt slipping No...

[landonshaw]

VP idle should be 850 +-25 RPM. I will verify tomorrow the idle speed and spray the belts to see if it might just be slipping.


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[stone beach]

which alarm is sounding ?? is there more than one (alarm) on that engine ??
not familiar with the engine but I would have expected several sensors but only one alarm...in which case you need to find out which sensor is triggering the noise

sounds more like low oil pressure at tick over ????

[landonshaw]

Did not think of the low oil pressure alarm. I will check. Thanks


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[landonshaw]

It is always happening when I can't take my eyes off of where we are heading, slip, mooring, anchoring. I will test Monday on the mooring and look at which alarm.


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[DougR]

Is the alarm being controlled by the primary alternator, or the secondary alternator, or both? Are they both standard VP alternators or some other brand?

Are the energize wires to the VP alternator tight? There should be a brown wire and a blue/red wire both connected to the d+/61 terminal of the alternator. These provide the energize current to the alternator. The brown wire runs to the alarm unit in the panel and is fed thru the charge lamp. The blue red is switched power from the key which runs thru a resistor and provides a backup should the charge lamp burn out, etc.

DougR

[Mycroft]

Nothing for it but to troubleshoot. Try and identify what exact alarm is sounding. Check voltage from each alternator when the alarm is sounding and when it isn't sounding. etc.

[tinkrman69]

Do you also have a warning light? if so it should come on or flicker if it were the alternator. If the alarm turns out to be the alternator and the belts and idle rpm are correct, I would suspect a liking diode in the regulator. I'm not all knowing, but I've never seen an audio alarm on an alternator. But todays world does have a lot of unnecessary gadgetry. ;-)

[gjordan]

Being another person that has never heard of an audio alarm for the alternator, I would suspect the oil pressure. If this just started after the rebuild, then it could be that the mechanic knocked a wire slightly loose or damaged an oil pressure sender. If you run it at the mooring to try to troubleshoot, and nothing seems wrong, then take the boat out and run it hard for long enough to get the oil hot and then put it to idle and see if the alarm sounds. Oil pressure sending units go bad sometimes or are easily damaged by a slipped wrench or dropped part etc. Do you have a manual for the engine? See what alarms it mentions. Of course I could be all wrong, so good luck. _____Grant.

[bootstrapper]

Hi It may be that now you have 2 alternators working the idle speed is a little lower causing the oil pressure alarm to sound,an alternator will make enough power at idle to slow the engine.It's unusual to find an alternator connected to an audio alarm, normally only water temperature and oil pressure though it's not impossible to do.

[landonshaw]

Yes I have a manual for the engine. A number of things to look at tomorrow. Luckily the are all rather easy to test out.


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[DougR]

Volvo Penta alarm modules have had three alarm functions for at least 25 years. The module drives alarm lights and audible alarms for:
Low oil pressure
High water temp
Charging failure

DougR

[hellosailor]

FWIW, "belt spray" is something you never want to use. It can only add dirt and gunk, or worse, it will actually rot the rubber in order to provide more "grip". You are better off simply cleaning the pulleys and belt, and then making sure the alignment and tension are correct.

[gjordan]

Most (probably not all) oil pressure alarms are set to go off at 6 PSI, which I think is much lower than an alarm should go off at, but bad connections or a damaged sender could have it go off at a different level. That is why I suggested running the engine hard if you didnt get an alarm at the mooring. A could hard run might lower the pressure to a point that the alarm sounded. I was not aware that Volvo alarms would go off for oil, electrical and temp. My old Volvo was more than 25 years old. This forum is full of information. ____Grant.