Its all speculation now but I have a different scenario. I still believe that the aftermarket amp is the root cause of the failure, especially if it a real big amp, like in the 1000 watt or larger category.
Here’s the set up, the driver has the volume cranked up, has other accessories on like the heater fan and the head lights and is cruising around at low speeds and having to stop at red lights a lot. At these lower rpm’s, the alternator is not keeping up and the battery is draining.
At some point, maybe the driver showing off and accelerating hard, or just gets up to a higher speed where the alternator goes to full output to try to recharge the now almost dead battery and feed the amp and the fuse blows.
Now the computer does not command an amp output, all it does is regulate the alternators voltage. The current output (amps) is dictated by Ohms Law. Because the external resistance is so low (high load) the alternator is pumping out max current. When the fuse blows, there is a moment when the computer is sending max field voltage to the alternator and without a load, the voltage from the alternator is going to spike.
The spike is pretty much isolated to the alternator, but there is the feedback loop that the computer uses to regulate the alternator with and the spike will be felt on this and that could have damaged the computer.
As for the harmonic balance, it must have broken at the same time the fuse blew. If it started slipping before the fuse blew, that would have dropped the voltage from the alternator and that would have reduced the current out so the fuse would not have blown. After the fuse blew, the load on the alternator is gone so that would take the load off the harmonic balancer.
One last thing that we won’t know unless the customer fesses up would be that the fuse blew much earlier and the customer “crowbared” it with a heavy gauge wire, which he removed after the harmonic balancer broke and the battery went completely dead.
I took a quick look and that alternator is rated at 110 amps so an uncontrolled rate of charge which caused the alternator to hit that figure could be what blew the 100 amp fuse. That fuse is also there for that reason.
No matter the alternator or car, an alternator should never hit the maximum rate of charge. If it does it means the charge rate is not under control or there’s a mother of all shorts.
A maximum charge rate for more than a few seconds usually means something is going to fry.
That pulley thing is weird. Who would have thought.
The owner of the vehicle is my son-in-law. And he’s at the age where he takes care of his vehicles. He was just driving along the freeway when the vehicle lost all electrical power.
Oh! And after the problem was resolved, the amp was reconnected to the battery and the sound system works just fine.
Well? I suppose if the vehicle could run long enough the harmonic balancer would start wobbling and/or make noise. But the vehicle stalled on the freeway and was towed to the shop. So the balancer didn’t slip long enough for that to start happening.
OK @Tester…car was an 89 Firebird. Kid was driving it when the strange smell he’s noticed for quite some time got worse, then the car just quit like someone turned off the key and had no electrical power. Pulled it home and he and dad found a burned fusible link off the starter. Well, no fusible link laying around, but a piece of 10ga wire got the car up and running again.
Week later the strange burning smell kept getting worse and the car died again, this time after seeing smoke from under the dash. Now the 10ga wire melted, time to tow it to the shop. The melted fuse link fed power to the ignition switch, and from there fed several fused circuits at the fusebox. Disassembly showed a melted ignition switch, a few feet of wires crispy and melted together, but no damage after the fuse box. Ultimately found that the go-fast chrome air cleaner dad put on the car 10 years ago didn’t fit just right, but took years of driving to finally rub through the insulation on the coil power wire. Rubbed through just enough to arc but not blow the fuse, but drew enough current to overload the ignition circuit, burning the wiring and the switch and finally the fusible link. Dad and son didn’t believe it either until I showed them everything, and they drove the car out sans air filter.
Pretty interesting stories. Just goes to show there’s no end to the possibilities.
Regarding runaway alternators, some years back I went through 3 alternators on a 1975 Harley Shovelhead dresser. This happened over a 6 month period after replacing the failed voltage regulator and it ate on me quite a bit until I figured out the root cause of all 3 failures.