1993 Mercruiser 454 Bravo 1 Blowing Alternators?

[OMARiverRat]

Hello again everybody...<br /><br />Well, I'm glad I caught this problem at my slip rather than out on the muddy mo'. Just realized (Yes, right before the most popular boating day of the year) that my alternator has not been charging - - Voltmeter reading approx. 10 +/- volts while running. I never really noticed because while at the dock, the boat is hooked up to shore power and the batteries are always charged. Anyway, I came across a rebuilt alternator yesterday from a friend, installed it, fired it up, and the gauge slowly built up a charge somewhere between 12-13 volts at idle. I pull out of the marina, get on plane, and hit the button to retract the trim tabs and my radio shuts off. I look down at the volt meter and once again I'm not getting a charge. I checked all of my connections to the alternator, as well as the belt tension and everything checks out. I'm wondering if something in the electrical system is frying these alternators? I do have a perko battery switch - on one side of the switch are a pair of marine starting batteries, on the other side of the switch is a single deep cycle. <br /><br />Any help would be greatly appreciated. I'd hate to pick up another alternator just to have it fried... Unfortunately no returns on electrical parts!<br /><br />Thank you for all of your help....

 

[magster65]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

Has your battery been load tested?

 

[vipzach]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

Try isolating each starting battery and see what happens, you may have one of the batteries with a dead cell and it is killing both of them.

 

[jeff13601]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

Are you sure that you have the right alternator from your friend?

 

[salty87]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

a shop will test your old alternator, for free around here.<br /><br />like the others have said, could be the batteries too. have them bench tested.

 

[OMARiverRat]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

Magster - I borrowed a load tester from a friend, and I'm heading down to the marina tonight to perform the load test. I'll keep you guys posted.<br /><br />Jeff, the alternators bolted directly in place of one another. The one difference I did notice between the two alternators is the new one (that worked for about 10 minutes) has a large chrome-finish box on the back of it. The original alternator does not. <br /><br />I'll check on that battery and keep you guys posted. Would a dead cell in the battery cause the alternator to fry itself?<br /><br />Thanks everybody.....

 

[magster65]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

A shorted cell will cause the alternator to charge at (or near) it's full capacity to compensate for the battery being 'weak'. They get hot and sometimes pack it in. I'm guessing this is what's happened.

 

[Boatist]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

What is the voltage on the batteries before you start?<br />A loss of connection to the batteries for even a fraction of a second will blow the alternator. So a loose or corroded battery connection, a loose connection on your battery switch, a loose ground to the batteries, a loose connection to the alternator.<br />Turning the battery switch thru off with motor running, and on some swtiches turning the switch at all with the motor running will blow the alternator.<br /><br />You say your batteries are always charged from shore power. So with the shore power off what is your battery voltage with the key on but without starting the motor? Again with the key on and the motor off run all your gear on board and watch your volt meter. If when you turn something on you see a big drop in voltage then you may have found your problem.<br />An extream over load could also cause the alternator to over heat. You can check for over load before you start the engine.<br /><br />An opean cell in the battery can also cause your problem.<br /><br />Hope you will come back and tell us what you find.

 

[OMARiverRat]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

I ended up doing a load test on all of the batteries, and everything checked out ok. One thing that was recommended by a local mechanic was to make sure that the alternator was charging ONLY the starting batteries. Then when floating downstream listening to the radio, flip the switch over to the deep cycle. Before firing it up and heading back to the marina, switch it back over to the starting battery. I replaced the alternator, and so far I haven't had any problems. The last alternator I had blew within 5 minutes, and this last alternator has been working for about a week or so. Hopefully this problem is put to rest. If it comes back you guys will be the first to know. Thank you all for your help. Take care!

 

[vipzach]

Re: 1993 Mercruiser 454 Bravo 1 Blowing Alternators?

That is cool, that has lasted a week now. I once bought three alt for my Trams Am(in a weeks time)before I got a good one. Kinda frustrating. Glad to here the good news though.