Dead after new battery installed

[natermitch]

Had to replace the battery last weekend. Came home from work on monday and went to fire it up and got absolutely nothing when I turned the key. I jumped it but it immediately died and essentially repeated that process for about five minute before hitting the internet. Current train of thought is that the terminal fusible link failed. I popped the cover to check the fuses and there was a 100A in the slot for the 140A Alt. and it looked like toast. I have a new unit on the way just wondering if anyone experienced anything similar and if that was the fix.

 

[Super77]

So someone other than you replaced the battery? And then you were able to drive it, but after that the battery was dead? I think you troubleshot correctly to the alternator, but I'm wondering how that fuse popped if it was good before.

 

[natermitch]

So someone other than you replaced the battery? And then you were able to drive it, but after that the battery was dead? I think you troubleshot correctly to the alternator, but I'm wondering how that fuse popped if it was good before.

So I replaced the battery myself and it started up no problem. Drove it around a little bit that evening. Two days later it was dead in the driveway. Went to turn the key and got nothing. I am wondering if whoever installed the 100A in the alternator spot did it to just get back on the road and never bothered getting the correct 140A replacement. I'm assuming the new battery surged it and blew it. If I am wrong I guess I'll be looking at ripping out the alternator. It's just weird because I have had alternators go out on other vehicles in the past and I wasn't dealing with any of those symptoms.

 

[Super77]

yeah, first right-size the fuse and then monitor. But something still seems off. If: works fine → drives for 1–2 days → parks → dead battery → blown fuse, that suggests the alternator stopped charging before the fuse failed. Maybe a loose B+ cable or terminal was not tight and arced? Maybe the alternator was marginal and the new battery revealed an issue like a diode, stator, or regulator?

But those are edge cases - start with the right size fuse and have the battery trickle charged back up to voltage if you can. And put a DMM on the alternator + lug when the engine is running to verify you're getting 13.5-14.2 VDC.

 

[natermitch]

Took me some time but the new alternator went in, in combination with the new fusible links in the terminal box. We are back in business. I ended up just moving forward with the alternator after being reminded that I had thrown a few random lights on the last drive before it died on me. Seems to have done the trick. I appreciate the help.