Alternator short?

[docg]

Been working on my boat and disconnected the battery. When I tried to hook it up the alternator started smoking. I quickly disconnected the battery. couldn't find any melted wires. When trying to hook up battery get big sparks (a short somewhere). Un hooked the Big red wire on the alternator and battery hook up is fine. every thing works. Got a new alternator installed it and have the same problem. Unhooked all alternator wires. Hooked up the battery cables. When I touch the Big read wire to the insulated Battery (B) post on the alternator, I get a big spark. Do I have a short in the new alternator???<br /><br />This is a 1988 mercruiser 4.3, New Mondo 3 wire alternator. Boat had a history of decharging the battery if left hooked up for long period of time.

 

[Dunaruna]

Re: Alternator short?

Hi docg, Welcome to iboats!!!!<br /><br />Don't try and connect the battery again, there is a method of finding shorts without connecting the batt.<br /><br />EXACTLY what work did you do? This will determine where to start looking.

 

[Chris1956]

Re: Alternator short?

dogc, I have the same motor as you, and have had an alternator start smoking. After I replaced it however, I had no further problems. I would first check to make sure the red wire on the alternator is connected to the positive pole of the battery. The wire should run from the alternator to the "hot" side of the starter solenoid. The red battery cable is also connected to that spot. Make sure you are connecting the battery correctly, red to positive, black to negative. If so, you need to get an analog ohm meter and find the short. Test the alternator red wire to ground, using the red ohmmeter lead on the red wire connection (disconnect wire first). There should be high resistance. If not, the diodes are likely shorted.

 

[Bt Doctur]

Re: Alternator short?

sounds like the cables were reversed somehow.

 

[jastacey]

Re: Alternator short?

I have had alternator issues in the past, first check all the wires from the baterry to alternator, wires from alternator to starter , be sure to check wire insulation, look for rub throughs or knicked wires, and check the wire hook-up

 

[goinhungry]

Re: Alternator short?

Doc- had the exact thing happen to me, same alternator type. It was dark and my buddy connected to the wrong battery terminals. Smoked the alternator. I couldn't believe that that was what caused it, but the guys on this site insisted that this is what must have happend, and low and behold, when I checked it the next day I found that he'd flipped the battery around when putting it in the boat! Lots of grreat knowledge on this site!! I'm on my 2nd alternator now, and it still instantly shorts/overheats when the engine is running (not upon connection to battery, or when the key is turned to accessory power only (even with the battery hooked up properly ). Its just an issue that I'll have to diagnose this spring since it's put up for the winter, but some here suggested in the past that it's either caused a short in the wiring somewhere, or maybe even in the starter, which in turn affects the alternator (since they're connected). I'm newbie enought to boating in general, so I'll have a heck of a time diagnosing this problem, but if I learn anything I'll keep you posted. If you figure anything out, likewise, keep us posted too. Good luck