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Bad Alternator - Mercury 150 Fourstroke

Discussion in 'Do-It-Yourself Projects' started by kaydano, Jul 1, 2017.

  1. kaydano

    kaydano Well-Known Member

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    A couple weeks ago I noticed my battery voltage was always in the 12s, even with the motor running.  Should be 14+ when the alternator is running.  Something wrong with the alternator...


    Took the boat home to check it out.  Some quick tests confirmed my suspicion.  It's about 9 pm, but I run it down to the dealer anyway (as I work the next day) and I just left it in the lot.  Only a couple of other boats in the lot in front of the service garage.  I figure they'll get to it quickly. 


    I call them first thing the next morning they tell me they have a 3 week waiting list!  But, they tell me they'll try to look at it in a week.  I tell them what I think is wrong, and tell them to fix it if under warranty if that's the case.  A week goes by, and they call and say it needs a new alternator.  Warranty on electrical stuff just expired, so it will be $400.  And they don't have one in stock and it would take a few days.  I wanted them to change the impeller too, but they just sold the last one.  So, a bit frustrated that I've missed a week of boating season, and sounds like it could be another week, so I tell them forget it, I'll come get it and take the alternator in to a local starter shop.  They charged me $55 to tell me I had a bad alternator, which I already knew. 


    I took it to the starter shop and they fixed it the next day.  2 bad diodes in the rectifier.  They had trouble finding a new rectifier (they normally deal with cars), but were able to fix it for $88.  Much better than $400, and I didn't have to wait any longer. 


    I took the alternator home, put it on the motor, grabbed a neighbor to go with, and we ran the boat down to the lake.  Start the motor.  14.4v on the fish finder.  Everything works.  Met some other neighbors just coming off the lake, so they jump on my boat and we head out for a nice night cruising around.


    I got really busy at work that week and didn't get back to the boat for a week.  When we got down to the marina the next time out, they said the battery was dead.  ???  I had just put a brand new one in this season (old one was 6 years old) and fixed the alternator....  They put a quick charger on it and said they'll leave it charge for 20-30 minutes and it should start.  While waiting, I take the cowl off.  Alternator is warm to the touch.  Everything else in the engine compartment is cold (they couldn't get it to turn over).  After it charges a while, we dip it in the lake, it starts, voltage is up and looks good.  But the warm alternator is weighing on my mind.  It should not be warm like that, and a new battery drained dead over the last week, so I decide to skip the boat trip on the lake and take the boat home and bring the alternator back to the shop before they close. 


    When I get home (an hour after dipping in the lake), the alternator is so hot I can't touch it.  I disconnect it, and take it back to the starter shop.  I wrapped it in a towel so it would still be hot when they took a look at it.  They were surprised how hot it was, but they tested it, and said it was putting 40 amps.  They said to check the voltage sense/reference and ignition/field terminals back at the boat and make sure it's not something with the boat.  I go home and do more tests.  Voltage reference pin is hot (which it should be all the time).  The field pin only has 12 volts when the switch is on.  That checks out.  I put the alternator back on, it immediately starts to get hot.  I pull the connector (but left the main battery charging wire attached), and it cools off.  I'm thinking there's internal short in the alternator somewhere.  Probably a bad regulator since the rectifier was just put in new and it works when the engine is running, but overheats when the engine is off.


    Rather than mess with it more (the new rectifier was an odd fit, but it worked, and I was suspicious that might have damaged the regulator) so I decide to just order a new one off Amazon.  Factory original was only $230.  I ordered it this Monday out of Miami.  UPS tracking shows it still in Florida right now (Saturday)!  I'm not likely to get it until mid-late next week, and we're going on vacation the following week.  Bummer.


    Slow start to boating season.  Someone else here posted something about an alternator bracket recall where they also replaced the alternator too.  I could not find any info on that recall.  Anyone know more?  I also can't imagine something being wrong with the alternator bracket, because mine is forged into the side of the motor...  Must be a different motor on the recall.


    The saga continues...  Hopefully we'll be on the water next Thurs or Fri, but then we're gone for a week.  Most years I have the boat out nearly 20 times by mid-July.  I'm on #3 right now...  I'll post an update later this week.


    If anyone has had a similar experience, I'd love to hear about it.
     
  2. Vikingstaff

    Vikingstaff Well-Known Member

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    I originally replied to this post you are referncing, and then Jack pointed out the thread had been begun almost 5 years ago. Thus, an old post and an old recall.  You are good on that part.  That said, sorry to hear about all the trouble you're having with your engine.  Not good, particularly around the holiday.
     
  3. lakeliving

    lakeliving Well-Known Member

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    What a bummer. Hopefully the new one solves the problem and you are good to go.
     
  4. BigKahuna

    BigKahuna Well-Known Member

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    I thought the Bennington warranty was bumper to bumper for 7 years?!? (When you bought your boat) Meaning if ANYTHING happened to it...........IT WAS COVERED!!! 
     
  5. cwag911

    cwag911 Moderator

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    Motor is under it's own warranty.
     
    1Blderbob likes this.
  6. kaydano

    kaydano Well-Known Member

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    Plus I didn't buy the motor with the boat. Good thought though!  Keep those coming, maybe I'll get a free part...
     
  7. kaydano

    kaydano Well-Known Member

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    Ha ha.  Didn't see that post was 5 years old!  At least I can stop looking now. 
     
  8. Rockie69

    Rockie69 Well-Known Member

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    I think it's the nut behind the steering wheel?!?!?!?
     

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