Wayward alternator

[flyboyjack]

So, here's my story and I'm stickin' to it!

About 3 months ago, my alternator began cycling from 14+ v to 12v and back. Always at low rpm, (idle to about 900rpm). Then it began becoming difficult to get it to come on line at all after starting. First it would take about 1200-1500 rpm. Then 2000rpm and then finally a RAPID advancing to almost max rpm to get the recreant alternator to "put out".

I removed said alternator, had it rebuilt and it worked 4.0 about 6 times. Then an exact repeat of the above.

I pulled it again and rebuilt again. Only worked one time and then nothing. I installed an aux ground. Nothing. Installed a jump-wire from the ignition in addition to the aux ground. Still DIW. Oh, before I forget: I pulled the alternator an additional three times and it bench checked perfect. Reinstalled on boat and DEAD!!

Consulted boat electrician and mechanic simultaneously, both at $90/hr!! Two hours and nuttin!! Mechanic suggested I use his alternator guy. I did. It "benched" 4.0 again!!. He suggested either an additional rebuild or purchase a new alt. I bought a new one.
First run,..worked perfect. Worked 4.0 for about a month. Now I'm back to "jazzing" the motor/rpm's to almost max rpm to get the alternator to come on line after start. It also has begun "cycling" from 14+vdc to 12.5, (battery voltage) and back at low rpm again.

So here's the deal: A McDonalds Happy Meal at the city of your choosing if you can analyze this conundrum.

Jack

[Sprig1]

Hi I'm sure they are smarter people here than me. But my guess would be a wire connection or burnt wire have you tried running a new wire from alternator to battery. Is the gauge bad? Do the batteries get run down? Have you load tested the batteries to see if you have a bad one in the bank. Get a cheap one from Harbor Freight it will load test the batteries and also tell you what the alternator voltage is. Hook it up at different spots and see what amperage you can draw. Be careful doing that you don't want to burn any wires. Do you have an ACR I think that's what it is or just a battery switch? Hook load tester there and see what happens. . Have you cleaned all the battery terminals and checked battery grounds. When the problem happens have you shaken the wiring harness.
I'm sure a good mechanic has already done all of this hopefully. It's always good to sit and look at the problem with another person. Two heads are better than one. Good luck you sure get an A for effort.

[RobS]

Where exactly are you measuring voltage? At the battery(s) or just relying on the helm gauge or what?

Have you checked the connections under the engine mounted circuit breaker?

Read both links I attach below. If you're not registed on the Seaboard forum you need to be, it's free. Between Seaboard forum and AOG you couldn't be better covered and a much better option than $90 per hour just to go nowhere..........

https://www.sbmar.com/community/topic/e ... t-breaker/

https://www.sbmar.com/articles/installi ... -dvm-boat/

[kerrye]

In 1977 I had an almost identical problem that drove me nuts on a 1969 Ford Econoline van. Turns out it was a bad belt which was slipping without screeching. Have you tried a new belt?

[flyboyjack]

Hey Folks,... sorry for the late response. We've been battling breast cancer here and by the grace Of God, we're kickin' the snot out of it!
I have completed via a certified "Yacht" electrician an almost total rewire of the boat, so all connections, lugs, corrosion, etc., should be above reproach. Voltage was checked at the back of the alternator AND at the batteries for verification. The battery voltmeter and chartplotter concur with the indications. I have replaced ALL 3 batteries. I have NOT shaken the wire bundles to check for shorts/grounding and I have NOT load tested the batteries because they are new. The connections were checked on the engine mounted c/b. (I will double check all connections there). The serpentine belt is new at about 125 hours and the belt tensioner is so tight that I doubt there could be slippage,... but again it's still way cheaper than another do nothing service call and it'll give me my backup. (It just seems weird that each time the alternator appears fine and then after a few uses begins to head "south" again. If I can figure out how to do it I'm going to replace two of the three wires, not including the unused tach wire. I'm thinking I'll just go directly from the back of the alternator to the battery bank with 8 AWG and bypass the starter connection and install a jumper wire to the ignition side. If that fails,...I'm out of ideas and "luck".

[robonurse]

I recently had the same (or similar?) problem. After a week or so of trying to locate the problem, I found the controller for the air heaters was stuck in the "on" position. I removed the controller and charging voltage returned to normal. I am considering leaving the controller out as I only use the boat from April to October and don't deal with any bitter cold weather.