GMT800: Pretty big fleet here, have a couple Tahoes, a Yukon, Suburban and few Trucks all factory equipped with 145 Amp alternators, and connected to main positive battery cable with "8mm sq" fusible link which looks about like an in between 12 and 10 gauge wire.
Tested output through stock alternator wire 105 to 110 amps at idle.
Upgraydd ( 3 rigs ) to awg SIX gauge cable from alternator and now each one makes 136 amps at idle.
............................... " Feels good man"

 

So, you are saying you upsized the fusible link ?

 

8.0 sq mm wire is actually between #8 and #9 AWG... That's a pretty massive FL. Since FLs are designed to be about 3 to 4 AWG sizes smaller than the wire they're protecting (i.e. about half the cross-sectional area or so), that's appropriate for protecting about a AWG 4 to 5, or about M18, main wire run.

3 AWG sizes is almost exactly a factor of 2 of CSA.

Here's a copper wire table for quick reference.

 

SO, what's the chance of my Alternator turning into a 145Amp smoke grenade ?

I really don't like undersized wires.

 

I have no idea at what current different sizes of FL would burn up at. But, the original was I think 5.0mm, so if that's right, 8.0 would take near twice as much of an overload to burn out, all else being equal.

As far as the "chance", that's really hard to say. Pretty low I would think.

 

It depends on the load. I'd say if you are drawing 135 amps at idle, there's a pretty good chance of smoke in your future.

 

136 AMPS at idle speed, loaded with carbon pile LOAD BANK.
With battery at full charge, no accesories running, fans OFF- just ECM and Fuel pump load was only 16 Amps.

 

I would think that where you'd possibly run into a problem, is when there's a fault. Normal operation I wouldn't think would ever get close to burning up ANY fusible link; that's why the factory sizes the parts, and the wires, and the FLs, they way they do. It would be one of those "edge case" kind of deals. And it'd be a damn shame if your car burned down instead of the fault protection working like it's supposed to.

As far as "chance", well, the "chance" of ever getting into that kind of situation, is pretty low to begin with. Then, the "chance" of a fire or whatever, is some fraction of that. Still, it could be a matter of life and death. Now, the factory has to think, what does a death claim cost and how many are they likely to have to pay, vs what it would take to alter the vehicle design (think Pinto gas tanks), over a production run of MILLIONS of vehicles. Trying to turn that around to the probability of ONE vehicle is a mathematical JOKE. Just the same, I wouldn't want to be the ONE.

Risk vs reward... we all have to figure out where we fall on that sliding scale. Speaking strictly as someone that's been hit by lightning TWICE. Not a full hit out in the open, mind you; both times, I was kinda inside broadcast transmitters, and it hit the antenna and came down the transmission line and I was there to complete the path to ground; but still, it HURT. The 2nd time I felt it necessary to check my heartbeat when I came to and picked myself up off the floor. My first wreck was also rear-ending a Pinto, which then rear-ended ANOTHER Pinto in front of it, and NEITHER ONE blew up! It just wasn't my day.

 

Besides "safety" the manufacturer is sizing everything as cost effective as possible, so if they can get away with smaller and cheaper they will if it satisfies the requirements. Then the aftermarket installer comes along and starts adding some lights and a winch and factory electrical is no longer satisfactory.

Very low chance of alternator lighting up, I think they can only really seize up or diode's can pop, but that's very rare. The next failure point is the wire itself which would have to short somehow, and barring an extremely bad front end collision or tree crunching your hood that wire shouldn't be touching anything else really.

 

The reason I said that is because I thought you had a situation that you had such high amp draws at idle normally.

I had one of my 135A alternators went up in smoke at idle. I don't know what burnt, but the back of the alternator was covered in soot. I was waiting in the grocery store parking lot, idling with the A/C on and I have Spal dual 16" electric fans. I have a heavy cable going straight to the battery from the alternator output. That alternator must have been on its way out anyway, I haven't had that happen since.