Is my alternator dying?

[vechnyak]

My 3ym20 has stock 60amp alternator. It would normally put out about 17-20amp after heating up. Today after about 1+ hours of motoring i noticed it was only putting out about 9-10amp. Infrared thermometer was reading 215f off the front by the pulley, about 180f on top. I could not get a good reading off the back.

I left the companion way steps off and mounted a clip on fan blowing at the alternator. Temps gone down to about 170f but amperage did not increase by much at all.

Question if these signs indicate my alternator is dying?

[SailingHarmonie]

Alternators rarely get "sick". They either work, or they die.

The most likely explanation for what you see is the batteries are getting full. Is there a reason you are not considering that possibility?

[vechnyak]

House battery was at 80% at the time. Alternator doesn't know anything about house battery. There's victron dc-dc charger between started and the house.

I will check the victron settings though!

[Ballsnall]

Originally Posted by vechnyak

Question if these signs indicate my alternator is dying?

Worn or dry bearing would cause a temperature increase but this is 'usually' accompanied with noise and vibration. Check your belt tension as this can generate heat as well and you said it was hottest near the pulley.

The lower amps could just be that your batteries getting full and the charger was backing off.

The temperature does seem a bit high though.

[vechnyak]

Ok so I just got back from the 2 week cruise. Before the trip I bought an old 55amp Hitachi to have as back up. I did not need to use it but i do believe my original alternator is on its last leg. Voltage never goes above 13.5 and amps start at 17 and go down to 14 amps when hot.

[Ballsnall]

13.5v is on the low side of normal range so it just depends on the dc-dc charger demands. If your charger is only drawing 10 to 15 amps then it would appear you alternator is working normally.
What was you house state of charge?
How long were you running the engine each day and what was the house draw?
Did you house bank go flat during the 2 weeks?
Do you have any other charging sources?
Was the alt temperature still running over 200⁰?
Did you adjust the belt tension?
Is the alternator noisy?

If you think the alternator is faulty just change it out, you have a replacement anyway. You can take it to a shop and have it tested which will give you a definitive answer. The winding insulation breaks down over time and this could be your issue.

[hlev00]

Check the pulley on the original vs your spare. You may need to swap them.

[Wotname]

Originally Posted by vechnyak

Ok so I just got back from the 2 week cruise. Before the trip I bought an old 55amp Hitachi to have as back up. I did not need to use it but i do believe my original alternator is on its last leg. Voltage never goes above 13.5 and amps start at 17 and go down to 14 amps when hot.

We really don't have enough data to determine the health of your alternator but as others have posted, they usually work properly or not at all.

Your stock Yanmar alternator is dumb and they do not directly alter the current output based on internal temperature. All they do is to wind back the regulated voltage as the temperature of the internal regulator increase. The gradient is -0.01V per degree C.

The current output is determined by the load on the alternator (within the limits of its design). Decrease the load, the current goes down and vice versa. As the batteries charge, the load presented to the alternator decreases.

To confirm if your alternator is working correctly, measure its output voltage when the case is cold, immediately after start up (while checking the current is below the rated max of the alternator), it should be around 14.4V. A cold alternator voltage of around 13.5V suggests the internal regulator has failed.

[vechnyak]

Originally Posted by Ballsnall

13.5v is on the low side of normal range so it just depends on the dc-dc charger demands. If your charger is only drawing 10 to 15 amps then it would appear you alternator is working normally.
What was you house state of charge?
How long were you running the engine each day and what was the house draw?
Did you house bank go flat during the 2 weeks?
Do you have any other charging sources?
Was the alt temperature still running over 200⁰?
Did you adjust the belt tension?
Is the alternator noisy?

If you think the alternator is faulty just change it out, you have a replacement anyway. You can take it to a shop and have it tested which will give you a definitive answer. The winding insulation breaks down over time and this could be your issue.

• House battery state of charge was around 80% (thats according to the phone app which is connected via bluetooth to the BMS of the battery.)
• The DC-DC charger is Victron Orion which I specifically selected to limit the draw to a max of 30amp from the alternator.
• 15amp from the alternator would be on a low side but would be OKAY if it was putting out over 14v which it does not.
• Did you house bank go flat during the 2 weeks? << no, never. My house bank is 200ah LIFEPO4 and I use about 5-6ah (when all systems are running) much less so at night (LED anchor light, fan, phone charge)
• Do you have any other charging sources? << sadly no.
• Was the alt temperature still running over 200⁰? << yes. but note that > 200f was directly from the front, top and back was at about 170f
• Did you adjust the belt tension? << no i did not, belt is not shedding any black rubber and the deflection is normal.
• Is the alternator noisy? << no audible signs of any mechanical malfunction.

[vechnyak]

Originally Posted by Wotname

To confirm if your alternator is working correctly, measure its output voltage when the case is cold, immediately after start up (while checking the current is below the rated max of the alternator), it should be around 14.4V. A cold alternator voltage of around 13.5V suggests the internal regulator has failed.

ok i will do that. For this test, should the engine be just idling or rev it up to normal cruising 2900rpm?