150 4s w/70 hrs- Alternator Toasted

[moymurfs]

Ser # below
Had the motor idling on the hose. Peeing great. I get System Fault, Low Voltage. Shut it off, didn't look at the voltage on the merc gauge but I have a digital meter that has always read the same. It was saying 12.6 volts. The motor has always read over 13v. Turned off the battery switch. Could get a slight whiff electrical burning every-so-often. Checked every wire in the boat. All were cool, no smell. Pulled the motor cover and starter & solenoid were kind of hot. Bendix wasn't engaged and no signs on the flywheel or bendix teeth that they were grinding. Went over to the alternator side and it was super hot & smelly. No alternator wires or connectors had any signs of excessive heat. Did a search and found others had experienced the same thing from the time period this motor came out. The motor itself is new-(replaced by Merc a couple of years ago. However, I'm sure they just reattached my 2016 components to the new engine.
Question: Are these alternators internally regulated? Can I get by with a new alternator or is there a separate regulator I would need to get? I'll bite the bullet and stick with the OEM Merc parts.

[mactlman]

likely internal regulator-- new one and a fresh belt should fix you up. should check the fusible like in the same area if it has one. Don sell everything mercury also

[Stradic4]

Welcome to the 150 FourStroke alternator failure world. I lost one at 50 hours in 2015 and that one at 180 hours in 2023. Yes, both got really hot when the RECTIFIER failed in both units...be careful touching one. You can Google "CT084-33 rectifier" to see what it looks like.

Be prepared for 350.00+ new OEM alternator...first one was 280.00 back in 2015.

I recommend OEM given the RPM these spin at. Don will have fresh stock with hopefully a more robust (latest with higher amp rated diodes?) RECTIFIER. Surely, Mercury was aware of the initial (3+ years?) failure rate and made a change.

The bottom bolt closest to the block/flywheel goes in first to almost tight but still loose. Stretch the belt by moving the alternator by hand so you don't crack the housing. It takes some effort using the palm of your hand to push it over center...will stretch tight then a slight bit looser after over center max stretch. The bolt torque values are:

Front and rear alternator screws (M10 x 60) 36.8 lb-ft
Nut securing fusible link to alternator 39.8 lb-in
Flywheel cover screws (M6 x 12) 88 lb-in

BTW Thanks for reminding me to take my two failed units to alternator shop to see if they are serviceable.

[yam911]

Yes, the alternator on your model motor is internally regulated. So just the one component is removed and replaced as an assembly.

Some alternators live forever and some just die a relatively early death.

[EuropeanAM]

And to add to the above comments:

-Nothing built in 2016 is really considered "new" today. Especially not electrical devices.

-There are numerous variables that can affect the lifespan of an alternator, and one of the largest is something you can control: DUTY CYCLE/DEMAND. Using a battery that EXCEEDS the requirements, is designed for the alternator's voltage profile, is cleanly and properly connected in a fashion that meets ABYC Standards, and that is CHARGED FULLY BEFORE EACH OUTING is an area you can control.