Alternator / Voltage Regulator

[davids2toys]

Pat, as usual, great posts. That MSD thread was good!

OK, so if it has a circuit breaker on the board that would explain why they want this to go directly to the battery thru no fuses or circuit breakers of any kind. So why are you running yours thru the protected side of the 50A CB? Why do we need to run thru anything at all? Is there any risk in doing what MSD says to do? I like safety, so I am more than willing to run this fusible link if it is a better installation. I just need to know how long to make the link?

It is not that I need to know what will fry the fusible link wire at all. I just need to know what to use for this application. So then my question is still this...per your chart, is Rick using an 18 gage (40 amp) fusible link to protect his 12 gage Red POS MSD wire?

Dave

[patrickt]

Originally Posted by davids2toys

So why are you running yours thru the protected side of the 50A CB? Why do we need to run thru anything at all? Is there any risk in doing what MSD says to do? I like safety,

...

... is Rick using an 18 gage (40 amp) fusible link to protect his 12 gage Red POS MSD wire?

The reason I feed the MSD box off the protected side of the master circuit breaker is not to protect the box itself but rather to protect the line that is feeding it. The onboard 15 amp fuse protects the box. If there is an internal short in the box, the fuse will blow, the car will stop, and that will be that. BUT, if the line that is feeding that box shorts out against the firewall then, absent the master circuit breaker, the battery will give all the amps it has (and remember that is hundreds of amps) and I will have a big mess. The same is true for the ten gauge wire running eventually to the fuse box. There is never an occasion that I want more than 50 amps coming out of my battery (the starter solenoid feed to the starter motor doesn't count). That's why the master circuit breaker protects everything except the starter solenoid feed to the starter motor. The added resistance of the circuit breaker itself is negligible. Now, I'm not so concerned about my alternator feeding a massive short because it can only muster 60 amps anyway. And, truth be told, most of the car wiring could handle 60 amps anyway. Remember, what a wire can handle is a function of its gauge and its length. Most of the wiring in a Cobra is pretty short (except the stuff running to the back of the car). So, for me, it's the battery I have to watch out for, and that's what the master circuit breaker does. Here's a nice little chart that shows you just how much some of our short, skinny wires can actually handle. And I'm not completely sure what Rick's set up is, so I'll let him describe it again.