Possible Alternator Damage?

I was replacing my stock 80 amp alternator with a remanned high output 100 amp type (140 amp). When I was moving the wiring from the old alternator to the new I forgot to disconnect the battery and I touched it to the block with my wrench and caused a popping short. But wait there's more, when I did finally get it all buttoned up after disconnecting the battery, I go to reconnect the battery, and the ground and power wires burn through microcracks in each other's insulation and cause shorting for about 10-15 seconds before I realized. The alternator now holds at 13.4 and goes up to 13.6 when I blip the gas. I asked my mechanic friend and he said I probably fried my voltage regulator but the internals of the alternator should work given a new voltage regulator. So I was just wondering you guys think the internals of the alternator are toast or just the regulator. Any input is appreciated

I'd replace anything that looks bad or might be. Even if you have free towing, having to take a vehicle that's broken down to an unknown shop which you may never go to again is setting yourself up for a rip off. Really worst case but why risk it.

Also, I'm personally not in favor of larger alternators unless you've add significant electrical loads. It does not produce is rated output till high up in the RPM range. It's just extra weight the engine and belts have to turn every time the engine changes speed. A higher rated output does not mean better quality either.

You can always take it back out and have it checked at an autoparts store. I would seriously consider replacing both cables if you had shorting overcurrent issues happen like that. 13.6v is the bare minimum to charge the system. So, you probably have damaged the alternator. An alternator with that current rating should be higher voltage like 14.2 at idle.

It does depend a little on ambient temp though Dave. Quite a few of the newer style internally regulated alternators will reduce the voltage as things heat up. My Denso did that, my Mechman does it, with the Mechman dropping far more than I like, need to put in the bypass setup Eric sent me still, so I can set and forget the voltage. A friend's Toyota's with 80-100A's on both, factory units, barely even charge at 13.2 at idle, kinda worries me.

Usually a fried regulator will be far more off the target. What was the charge voltage before the swap, with the old alternator? Is the new one the Bosch or Denso? You mention it's a 100A style but 140A, makes it sound like an aftermarket. Does the aftermarket supplier give any specs? Either way it's charging still, and the regulator will usually fail in a go/no go situation from what I've seen. You may want to check that the rectifier circuit isn't damaged, with a quick AC voltage check on the system.

DEFINITELY replace the cables though, no question on that.

If you shorted it out while it wasn't running, I'd guess that the alternator and regulator are fine. You +12v battery-to-starter-to-alternator and alternator-to-block ground wiring may be toasty. You should replace, at least, the toasty-ist piece if you see visible damage. If you shorted it out while running, it may have damaged the alternator (specifically, the diode bridge).

You can find cigarette lighter USB plugs with a voltage display on ebay/amazon for less than $10. Easy way to keep an eye on the charging voltage and to spot low voltage problems.

Update: The ground was loose :facepalm: Now it holds at 14v cold and goes down to 13.6 as it warms up with a rev goes up back to about 13.9-14ish. Much better, still not great, but I don't think I damaged anything (majorly anyway). At full load, however, (hazards, lights, radio, ac, elc fan) It goes all the way down to 12.2. It still goes up with rpm, but a little too low for my liking. Just ordered an adjustable voltage regulator to try to keep the volts up, we will see what it does when it gets here.

12.2 is actively discharging under load.
Reman quality on accessories these days are terrible, I honestly trust used parts more. Just had a reman Bosch alternator putting out 12.x volts on a buddies car a week after install.

What ^^^^ said. Reman stuff is utterly junk. Not being able to hang when it's loaded, but charging fine under no load makes me question the 'high capacity' statement of the build.

Just the charging voltage alone doesn?t tell you much more than the alternator is working or dead. If the battery is old and weak there could be significant current going into it even at 13 Volts. Also, a high charging voltage in hot weather can over heat and damage even a good battery. That?s why the regulator varies the charging voltage with ambient temperature. A search should find some graphs of proper charging specs.

gsellstr said:

What ^^^^ said. Reman stuff is utterly junk. Not being able to hang when it's loaded, but charging fine under no load makes me question the 'high capacity' statement of the build.

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Yep. The only good thing about the lifetime warranty is you can swap out as many times as you need until you find a "good one".