3 rebuilt alternators in 2 weeks what keeps blowing

[cruisersveesport]

I have a 1987 cruisers vee sport with a 454 mercruser and bravo 1 setup.

I replace my alternator almost annually. This year I am having a problem. I tried to replace the Mandalay 4 wire alternator with a GM 1 wire. It will not work for more than 15 minutes and it dies. My Starting battery is new, my accessorie battery is 2 years old.

The alternator is wired 1 feed to the Isolator, The other to the wire harness to power the boat. The other to wires are just hanging and sealed.

I went to a shop and picked up the alternator. It burned out, I took it back and it was repaired an tested out fine. It blew again after 15 or 20 minutes.
I then purchased my own rebuild kit and it also blew quickly.

I checke the Stator it was fine.

Anyone help please?

 

[Reel Poor]

Re: 3 rebuilt alternators in 2 weeks what keeps blowing

There may be a problem with the isolator or your battery switch. Wire around them directly to the battery (be sure to disconnect the battery lead(s) from the isolator to the battery switch(s)) and watch whats happening at the battery with a volt and amp meter.

 

[Don S]

Re: 3 rebuilt alternators in 2 weeks what keeps blowing

The alternator is wired 1 feed to the Isolator, The other to the wire harness to power the boat. The other to wires are just hanging and sealed.

Could you explain in more detail exactly how the alternator is wired to the isolator? It sounds by your above explantion you have more than one wire from the alternator going to the isolator.

 

[Boatist]

Re: 3 rebuilt alternators in 2 weeks what keeps blowing

With a one wire alternator and a battery isolator you would normally connect the alternator to the common on the isolator to charge both batteries. Then everything would run off one of the batteries.

Make sure both your Batteries connections are clean an tight. I belive the number one cause of blown alternators is battery switches and how they are used.

Do you have a battery switch?

 

[cruisersveesport]

Re: 3 rebuilt alternators in 2 weeks what keeps blowing

I have a wire directly to the isolator and one that comes off to the guage on the panel. This is also wired to the other guages in series. There are 2 wires left over from the mando alternator. one is an excite wire the other unknown.