Voltage dropping

[mjsti]

Last evening I had the boat out and noticed the voltage gauge dropping 2-3 volts while high rpm's, then going back up at idle. I'm suspecting its the alternator as the last time I had the belt off I noticed the alternator bearings sounding rough, and already have one on order. Can anyone confirm this as the likely culprit or anything else I should be checking, aside loose connections, etc?

Not sure if its recommended or not, but I've kept it switched to both batteries. Once I install the new alternator, should I switch to just one battery at a time to reduce the charging load?

Finally, at what voltage will the engine stop running, 9, 10 volts?

[Fiveflat]

I have first hand experience with this as of last weekend. I had a similar situation and turns out my orange lead off the alternator was loose. It was arcing and burned up a little bit.

Anyrate, when my gauge got to 10 volts, a warning started beeping. Just below 10 the warning beep was continuous for about 30 seconds to a minute and then the motor shutdown. I pulled out my oars...

[mjsti]

Thanks, that's good info to have for future reference. Last evening when I noticed the low voltage I switched to one battery "just in case" and was getting close to 10V. Restarting the engine was getting sluggish as well. I'll go through and verify all connections are tight when I swap out the alternator.

For my reference, what voltage should I be seeing on the gauge while running at higher RPM's, 13-14V?

[Fiveflat]

I don't know if our boats will vary at all, but my gauge is just a little above 14V when I'm running over 2000RPM. Hangs out around 13V at idle.

[bigdaddy_houseboater]

You ordered a Mercruiser ? MP alternator? What did that set you back?

Typically, you can get them rebuilt in most localities for $50-$75.

I don't know if our boats will vary at all, but my gauge is just a little above 14V when I'm running over 2000RPM. Hangs out around 13V at idle.

[Fiveflat]

I didn't replace my alternator. My issue was the loose connection on the orange wire.

[mjsti]

You ordered a Mercruiser ? MP alternator? What did that set you back?

Typically, you can get them rebuilt in most localities for $50-$75.

I ordered new online for ~$90 shipped. Not sure if that's a good deal or not, but it was quick and easy. I can PM you the link if interested.

[mjsti]

Forgot to mention, this is for a Mercruiser 350 mag mpi, but supposed to fit a number of other engines.

[Fiveflat]

I want to look into getting mine rebuilt into a 90-100amp alt. But it's going to depend on the turnaround time. I can't be without during any weekend... right now

[bigdaddy_houseboater]

Damned good deal for a marine application alternator.

I ordered new online for ~$90 shipped. Not sure if that's a good deal or not, but it was quick and easy. I can PM you the link if interested.

[bigdaddy_houseboater]

Thats why we have winter.

I want to look into getting mine rebuilt into a 90-100amp alt. But it's going to depend on the turnaround time. I can't be without during any weekend... right now

[mjsti]

Forgot to update this from last week... Got the new alternator installed, cleaned up the connectors and applied a thin coat of dielectric, and the voltage seems to be good now. At cruise the voltage stayed solid at 13+V and the only time it fell below was when we were trying to teach a newbie how to surf, lots of idle time. IIRC, they don't start charging until around 1k rpm...? I probably should put the batteries on the trickle charge so the alt isn't working so hard.

The only issue I had was the serpentine belt started to squeek. I'm guessing due to the newly painted pulley, but ended up getting a new belt (from local auto parts store) since the old one was well worn anyway. Test run on the fake-a-lake sounded nice and quiet. Squeeky belts drive me crazy!

Taking her out tomorrow for more "testing".

[rtmcdonald]

Taking her out tomorrow for more "testing".

How did it go? I'm having a similar issue and think I should replace the alternator. Can you PM me the link to the one you bought?

[mjsti]

How did it go? I'm having a similar issue and think I should replace the alternator. Can you PM me the link to the one you bought?

PM sent.

So far so good, has been charging nicely all summer.