New alternator?

Ok, so I just purchased my first very used boat. '87 Wellcraft 180. 3.0 litre mercruiser, 181 cid, serial number B451218. Not paying attention one afternoon getting ready for its maiden voyage, I momentarily hook up the battery backwards long enough to generate some smoke at alternator and starter. Switched everything back and engine started fine. Used the boat once for a few hours on a lake with no problem on a Wednesday, on Sunday before heading out checked battery and it is completely dead and wont take a charge. Got a new battery. Ran all day Sunday no problems (no electronics at all, just a half dozen or so starts and bringing the drive up and down a handful of times.) Not feeling comfortable with the previously dead battery and recalling my battery blunder I started to research here on iboats.
With battery disconnected 12.5 volts across battery terminals
battery connected at idle : 12.3 volts
2000 rpm : 12.3 volts

Current alternator has a single stud with 1 orange wire coming off. A purple and black wire have been cut back from alternator and taped off. It currently make a slight rattling noise which stops if I push on the alternator.

I cannot find an amp rating or model number on the alternator other than SAE classification on back.

Questions:

Should I suspect the alternator is bad and replace it.
Is there anything else I should look for.
Can anyone recommend a replacement model alternator for this engine. I am assuming from what I have learned that it is a "1 wire" style and the more amps the merrier?

Any information would be appreciated.

Rob

Re: New alternator?

"generate some smoke at alternator" - electrical devices need smoke - they seldom function once you let it escape. unless you can figure out a way to get some smoke back in there, it's safe to assume it's a goner.

Re: New alternator?

What's the voltage at battery when engine's running at 1500 RPM or above? IF not 13.5 or above, your alternator's diodes and or the regulator have likely lost their smoke.

Re: New alternator?

RWilson2526 said:

With battery disconnected 12.5 volts across battery terminals
battery connected at idle : 12.3 volts
2000 rpm : 12.3 volts

Click to expand...

It's Toast.

RWilson2526 said:

Can anyone recommend a replacement model alternator for this engine. I am assuming from what I have learned that it is a "1 wire" style and the more amps the merrier?

Click to expand...

You might be able to take it to a starter/alternator rebuild shop as you can normally get these things rebuilt. But since you don't have much way of telling what kind of output she has a brand new marine grade high output alternator is probably the way to go.

As a general rule try to avoid anything labeled "remanufactured" as typically these are alternators that have failed at some point and just the broken part is fixed. A good starter/alternator shop will replace all the worn componenets so either have it rebuilt or buy new when possible!

Re: New alternator?

Rob, Alternators have a set of diodes for rectifing the AC current into DC current to charge the battery. You damaged some of these when you hooked up the battery backward. if the alternator is newish, you might see if you can replace the diode body. You may be able to buy a replacement diode body, and will need to be able to do some soldering. Alternatively you could take the alternator to an automotive alternator shop and they can repair the diodes for you.

You might also check to see that your alternator is hooked up correctly. Single wire alternators did replace the ones with three wires, but you need to make sure your boat is wired for them. There was a conversion procedure, but I do not have it.

I like rebuilt marine alternators. They have worked just fine for me. I do not like rebuilt marine starters however. They have too much wear on the bendix, and don't work well.

Re: New alternator?

Thanks all for the information. Being that the alternator looks like its been around the block a few times I think I will spring for a new one. Have narrowed it down the following from Basic Power in NC. It appears to be layed out the same as what I have..... If anyone sees anything potentially wrong with this replacement I'm all ears.

Thanks again for your help.

http://bpi.ebasicpower.com/mm5/merchant.mvc?Screen=PROD&Store_Code=eBasicPower&Product_Code=MES3147M

Re: New alternator?

Should work fine.Ebasic sells good parts.Fast shipping too...

Re: New alternator?

is 63 amp as much as you can get? Do you have dual batteries? Personally if i were buying a new one id go for closer to 100 amp.

Re: New alternator?

Pond Tunes - I was sticking with Basic Power as they came recommended from a friend for the very reasons Gary had mentioned. In their offerings it seemed the only compatible unit they offered was the 63 amp. I do have only one battery. which seems to be all the boat ever had in its 20 years. I do have a small Humminbird fish finder and a stereo but thats about it. Dont really plan on being out at night too much so not worried about nav lighs and all.. We do like to run the boat when we are in it so I hope there will be alot of charging time. Well anyway, I already placed my order with EBasic and then for fun after reading your post started looking for 100 amp alternators. Found this one.....


http://www.db-starter-alternator.com/Items/10si-marine%20new?

Thats a serious price difference and appears to be functionally the same. I dont think I'll cancel my order but does anyone have any experience with this supplier...seems to be a lot of convincing in the description that it IS brand new.

Re: New alternator?

Okay, my turn... What drives the need for a 100 Amp alternator on a boat? In an automobile there are many current hungry accesories: Headlights, AC blowers, windshield wipers, etc. Even with dual batteries, do you need even a fraction of 50 A charge current for each? Unless there's a kilowatt amplifier on board, and MOST of that kilowatt of amplification is used, I don't see the need for that much current availability.

OR is it so the alternator only has to crawl along at WAY below its rated current and, therefore, is likely to last longer?

Just curious, won't help me with my outboard, lol.

Re: New alternator?

Wow that is a serious price difference, wonder what is up with that.... You should be fine with the 63 amp, with your setup unless dual (or more) batteries are in your future the 63 amp will be just fine.

Quad:

You're right in saying that most applications wont have major current draw such as headlights. However I didn't know what his application was nor what kind of accessories he was going to be using. Normally price-wise there isn't a huge difference in comparable alternators to get the extra 40 amps or so which just like in a car will meet any charging demand.

Just a suggestion and another route to consider!

Re: New alternator?

Agreed. If the price difference is marginal, go for the gusto! Less likely that a transient spike will take out the diodes, the bearings might be a little beefier, etc.