Alternator / Voltage Regulator

[RICK LAKE]

davids2toys Dave I don't beleive in 100 years that the MSD 6AL draws ONLY 1 amp for every 1,000 rpms. Why the heavy 12 gauge wire then???
Remember I said overkill, THis fusible link is also like a resistor and you loss ampage going though it. IT's like a funnel you are pouring a fluid through, pour slow and you have no backup, pour fast and the funnel fills. Same applys for electrical curcuits. This is why good connections are so important.
Curcuits are tested with a steady load, not with startup spikes. Your fans on your car my draw 15-18 amps but the startup may be as high as 40-60 amps for a split second. For this second the ampage is way beyond the curcuit limit. The fuses are slow blows and are the safety protectors of the curcuit. This only last for .10 of a second. Over time a fuse or link will weakin from the heat or spike loads. I don't explain theory very good, too many days of missing school.
Any way Yes a 16# link would be ok, just no for me. The link will still blow if a dead short happens. With 12 Gauge on this curcuit I don't believe in having any problems. Other power curuits, yes with running a lighter gauge fuse, depending on the wire of that curcuit. I like to match up gauges.
PS stop finding things on the car. You are 3 hours away, any more problems, I am sending Pat to fix your car.

[patrickt]

Originally Posted by RICK LAKE

PS stop finding things on the car. You are 3 hours away, any more problems, I am sending Pat to fix your car.

I'll have that thing up and running in no time -- using nothing but duct tape and coat hangar wire. No fusible links -- just a few fuses and one measly circuit breaker.

[davids2toys]

Originally Posted by RICK LAKE

davids2toys Dave I don't beleive in 100 years that the MSD 6AL draws ONLY 1 amp for every 1,000 rpms. Why the heavy 12 gauge wire then???
Remember I said overkill, THis fusible link is also like a resistor and you loss ampage going though it. IT's like a funnel you are pouring a fluid through, pour slow and you have no backup, pour fast and the funnel fills. Same applys for electrical curcuits. This is why good connections are so important.
Curcuits are tested with a steady load, not with startup spikes. Your fans on your car my draw 15-18 amps but the startup may be as high as 40-60 amps for a split second. For this second the ampage is way beyond the curcuit limit. The fuses are slow blows and are the safety protectors of the curcuit. This only last for .10 of a second. Over time a fuse or link will weakin from the heat or spike loads. I don't explain theory very good, too many days of missing school.
Any way Yes a 16# link would be ok, just no for me. The link will still blow if a dead short happens. With 12 Gauge on this curcuit I don't believe in having any problems. Other power curuits, yes with running a lighter gauge fuse, depending on the wire of that curcuit. I like to match up gauges.
PS stop finding things on the car. You are 3 hours away, any more problems, I am sending Pat to fix your car.

Rick, I am doing multiple jobs at the same time so I have multiple issues, sorry. I am not a 1/2 arse person , I like to do things right the first time and avoid learning stupid, expensive, potentially disastrous lessons.
You explained some of this well. I do understand about start up spikes vs steady running use and the importance of good connections.
Maybe I am an idiot but I still do not understand what you used when you say "40amp". Was this the fusible link wire I am looking at online? As I said, 40 amp equals a 22 gauge wire, so I am still not understanding what you used. So are you saying 16 gage fusible link wire(75 amp) is OK, but not for you? You would go with the 22gage(40amp)fusible link wire???

Yes, only 3 hours away...you are more than welcome, why don't you and Patrick come up and we will have a nice BBQ and play with my car...LOL. Also show you some awesome cobra driving roads. I have a lift if you want to put your cars up in the air to do any work or service

PS: Don't forget the duct tape Pat

[patrickt]

Originally Posted by davids2toys

Maybe I am an idiot but I still do not understand what you used when you say "40amp". Was this the fusible link wire I am looking at online? As I said, 40 amp equals a 22 gauge wire, so I am still not understanding what you used. So are you saying 16 gage fusible link wire(75 amp) is OK, but not for you? You would go with the 22gage(40amp)fusible link wire???

As you know, but I'll say it anyway, when an electric motor is turned on, there will be an initial, very large "surge" of current that will exceed the rating of the fuse. But, the fuse or circuit breaker won't blow because it takes a little more time than that to heat up the element and cause the trip. This is normal. For a dramatic demonstration, go here: 300 amp X 12 volt Circuit breaker and skip down to my post with the pic of my inductive ammeter set to measure the surge current of my starter motor (and it's the old style big guy that went in to five billion Ford cars). Yep, over 900 amps. So you know, any of our cars, even the ones with the little tiny 60 amp alternators like mine, can still crank out hundreds of amps, which can create enough heat to melt any of your wires. In choosing a fusible link, the reason you go with a gauge rating, instead of an amp rating, is because you are protecting the wire itself, as opposed to the load. A fuse will protect the load, so it's handy to just double the amperage for the load and set that as your fuse value -- even if you're feeding the load with a very, very large wire, or a small wire. Now with a fusible link, you ask yourself "what's the maximum amperage that wire will handle" and then place a fusible link along the line that will handle less than that but, of course, still exceed the combined load that is being served by the line itself. Most car wires, if you short them to ground, will carry quite a bit of amperage before they burn the insulation up -- much more than you might think.

[patrickt]

... and the MSD box really does only pull 1 amp per 1000 RPM. Here's a thread on the MSD forum where the MSD tech talks about it: https://www.msdignition.com/forum/showthread.php?t=4242

... and the box itself has a 15 amp fuse soldered to the board itself -- so there's no reason to add a fuse to your MSD box load because they've already done it for you.

[patrickt]

But if curiosity has gotten the better of you, and you just have to know how much current will blow a typical fusible link, or else you just won't sleep at night, I copied this chart for you.

[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.