new alternator?

[boatman37]

hello folks. looking to replace my alternator but not sure which one i need. i emailed the place i was going to buy from and asked them but they said they would need numbers and measurements. i am looking to buy from DB Electrical if that helps. i guess they sell rebuilt ones for about $60 and a dock neighbor has bought a few from them with no issues. my boat is in underground storage for a couple more months so part numbers and measurements will have to wait. not sure if the engine # will help or not but it is a 1986 sundancer 250 with merc 260 (#0A593759). it is mounted port side at the lower portion of the engine.

my dock neighbor has a 1989 sundancer 300 and told me to order the one he did but when i look up the part it seems 1987 is a different part number than 1986? pretty sure it is a 55 amp, at least thats what my manual says

any help or will i have to wait until spring?

thanks!

 

[airshot]

If you have a skilled rebuilder in your area, get the original rebuilt. Many of the aftermarket units are not as good of quality. When mine went bad I bought an aftermarket and after looking over it carefully I returned it and had mine rebuilt by a local rebuilder. Heck he even let me stand there and watch him rebuild it. The original is so much better built.

 

[achris]

Agree with ^^^^. Usually about the only thing that goes on an alternator are the brushes, sometimes the bearings, but they are both easy fixes, and well within the scope of any half reasonable auto sparkie. Merc used 3 different alternators (all 3 wire), a Prestolite (8EM2003KA), a Motorola (8MR2039K) or a Mando (AR-150) , but the bracket work and wiring are exactly the same for all 3.

If you do go down the aftermarket route (these are not rebuilt, they are cheap Chinese imports!), the orginal number of the Merc alternator was -92497A3 (supersedes to -817119A4). I have looked up a DB one and it looks like only one alternator is a direct replacement (so I don't know what the guy you spoke to was on about ), that's an AMN0002. But as we said, easier and better to rebuild your original....

Chris.......

BTW, 1986 and 1989 use the same alternator. 55A Prestolite, Motorola or Mando

 

[boatman37]

Thanks guys. when i looked one up before (think it was a Sierra) there was a different part number for 1987 and up. that was awhile ago so can't remember for sure. talked to my dock neighbor last night and he said he used the same alternator on his 1984 Wellcraft that he did on his 1989 Sundancer (both Merc 260's) so you may be right. Anyway, there is a local rebuilder so i will check that out too. not 100% sure mine needs replaced but for $60 why not? my gauge reads about 12 volts normally and about 10.5 to 11 with the bilge blower running and it is 30 years old. original owner confirmed he never replaced it. it very well could be the gauge or dirty wires but i did have an odd issue that was charging/battery related.

a couple of times last year after anchoring i forgot to switch the battery back to the starter battery and cruised away on house battery. after about 100 yards or so the boat just shut off. when trying to restart acted like a low battery so i switch batteries back to starter battery and it fired right back up both times and was fine. i was only anchored for a couple of hours with nothing running but my VHF so couldn't/shouldn't have drained my house battery that quick. my thoughts were that if the alternator wasn't re-charging my low house battery that after 10 minutes of running git didn't have enough to stay running? but then i think the alternator couldn't have been that weak? the longest trip we went on was probably 20 minutes so it is possible that it is only running on battery capacity then when we get back to the slip shore power charges it back up for the next day? the house battery is brand new. the starter battery was in the boat when i bought it so not sure how old it is but seems the house battery is the one that was dying on me.

i never got around to checking the alternator output but like i said, for $60 why not replace it to eliminate that possibility. i could then have my original one bench tested and kept for a spare.

EDIT: the dock neighbor bought the DB ADR0334 for his 1984 and 1989. its a 1 wire 105 amp

 

[achris]

Do not use a 105 amp alternator without upgrading your wiring.

 

[boatman37]

Thanks for that warning! Wasn't sure if that would be a problem or not.

 

[bruceb58]

I hate one wire alternators. You have to rev up the motor to get them excited. Prefer a 3 wire alternator.

 

[Rick Stephens]

I have rebuilt so many alternators over the years, that I can't but recommend you do that or have it done. I started doing it as a kid when I couldn't afford to replace an alternator, and as long as you get the right kit they are a snap to replace any of the parts inside. Brushes and bearings are the most common need. And so easy to install. Taking it to someone who can test the resulting rebuild is a step better. They can make sure it puts out correct voltage and amperage before you install it back in your boat. Get another 30 years out of it.

Rick

 

[boatman37]

Thanks guys. i had a 1 wire alternator on my 57 Chevy but it had low draw anyway. I will definitely call a local shop for a price. We used to have a great place a couple miles from my house that specialized in electrical systems but the owner died and they closed down. not even going to attempt it myself. i'm sure i could do it but i have enough other projects to spend my time on so i will gladly pay a pro

 

[boatman37]

Pulled the alternator today. it is a Mando AR-150. Mercruiser #98555.

 

[boatman37]

Looks like you are right on that AMN0002 #. i did call a local alternator shop and at first he said he couldn't give me a ballpark figure until he tore into it to see what was wrong. i told him i wasn't sure anything was wrong, just wanted it gone through after 30 years of use. so he gave a ballpark of $50-60 so i will drop it off to him and let them test it and go through it

 

[achris]

Have a close look at these wires....

 

[boatman37]

yeah i saw that. the wires look frayed right there. i haven't looked too closely yet but will tomorrow but did notice that as i was removing it. and thats how they were. none of that was from me. thats why i cut the wires before the splices so i could eliminate those old ones. i may replace that whole run of wires but have to trace them back to see where they go. it was pretty dark in the mines and i was working with a flashlight so couldn't figure it out today

 

[achris]

Errr, those 'splices' are actually bullet connectors, and can be just pulled apart. The wires they were attached to run into the harness, the Red to the main power circuit and the Purple to the switched power circuit (Key ON)....
Here is a wiring diagram.



Chris.........

 

[Faztbullet]

No motor/alternator rebuilder in my area will repair Mandos as told no parts for it.....

 

[boatman37]

Errr, those 'splices' are actually bullet connectors, and can be just pulled apart. The wires they were attached to run into the harness, the Red to the main power circuit and the Purple to the switched power circuit (Key ON)....
Here is a wiring diagram.



Chris.........

i was wondering that after i got home. hard to see in there with a flashlight when i removed it. i can just put new bullet connectors on them

 

[boatman37]

checked it out a little closer today and the red and purple wires are bare where they exit the back of the alternator and pretty sure the bare wires were in contact with each other and possibly with the alt. case. what problems could that have caused? like i said, i really didn't have any noticeable trouble with it except a little low reading on the volt meter

 

[achris]

The red and purple touching would have left you with a 'key ON' situation when you turned the key to OFF (the engine would not stop). If either were touching ground, popped breakers and fuses.

Low/no output is usually a sign of internal issues, like brushes (which are still available)....

Chris........

 

[boatman37]

hmmm. i had no issues like that but they definitely had to be touching as they were bare wires and were even twisted around each other. there is a 3rd wire that comes out that may also have been making contact with those two. it is possible that some of the insulation broke off as i was messing with it so maybe they weren't touching before that?

 

[ottawamerc]

I had the same unit on my 87 SeaRay and it quit due to the voltage reg on the rear of it. I bought a new regulator off of the internet somewhere and it only lasted for a few hours then quit again I bought an aftermarket unit from a local shop, upgraded my wiring since it was a higher amp unit and now I'm fine.