SF Alternator Upgraded Wire Size?
 

I just looked at some old build sheets on alternator size and SF recommends nothing bigger than 65 amps. Anything bigger may fry the wires and amp meter if there is a problem.

Their recommendation is another 10ga wire run along the current wire and change the amp meter to a voltmeter. With that said my 150 amp is stupid over kill, it was recommended by Prestige. I don’t really want to rip the dash out to change the amp gage to a volt gage. Plus, why not use an inline fuse to protect the wires, hmm

Any idea if SF upgraded their wire size to allow larger alternators without frying the system in case of a problem? Also any idea what the max size alternator the Smith amp gage can handle.

If the wiring hasn’t been updated what size alternator is best to run everything?

Heat fan: 5amps
Rad fan: 24 amps?
Lights: 6 amps
Ingnition: 4amps
Total 40 amps sound about right?

Thanks

David

It doesn't matter. Here's why: Even if you had a 500 Amp alternator, that doesn't mean it's pumping out 500 amps. If you have a 40 amp load on the system, and your battery is fully charged, your alternator will be putting out maybe 42 amps. And how many amps will be going through your ammeter? Only two. That said, I am a proponent of a shunt wire around ammeters in our cars. You can read about that in this thread: http://www.clubcobra.com/forums/era-...ator-gage.html

The most likely scenario I can imagine where you might overwhelm the ammeter and/or wires would be by adding some high amp accessory. Or you might jump start the car with a nearly dead battery and then turn on every electrical accessory while you drive the car to recharge the battery. In all other high demand scenarios (e.g., a dead short in the fan wiring), a fuse should blow before the wiring overheats. Multiple simultaneous failures are theoretically possible, but unlikely. . . . Some cars have a inline fusable link for such events. As I designed the entire electrical system for my Cheetah, I included an 80 amp fuse between the alternator/battery and the main bus, and I used a voltmeter instead of an ammeter.

Voltmeter versus Ammeter
 

The voltmeter versus ammeter debate has been around forever and hashed out here many times. The main drawback to an ammeter is the safety aspect. A good shunt wire will take care of that and there are aspects of an ammeter that are desirable if you know what you're looking at. My ammeter tells me a ton of information, but only because I've been watching it for almost 20 years under a variety of conditions. That said, there are still times that I'd like to know what my voltage is without having to hop out of the car and hook up a VOM under the hood. That's when I plug in my little cigarette lighter voltmeter that also happens to have two USB outlets in it as well, just in case I need to charge my phone (which has never actually happened, but could). The combination of having an ammeter and a voltmeter together can't be beat when you're trying to diagnose an electrical problem -- real or perceived. But for 99% of the time, I run an ammeter alone.:cool:

https://i.imgur.com/8lNCP9a.jpg

https://i.imgur.com/uwk4e6Q.jpg

I have the drop down console push button start option and there is an extra port where people put in a volt meter.

Not sure why SF doesn’t instal a shunt on the amp meter. I’m not exited about ripping the dash apart on a new car for it unless I can wire it in on the outside possibly firewall.

Check the wiring diagram from Blas and there's bound to be a short cut for the shunt wire. All you're doing is bracketing the ammeter so you can do it almost anywhere on each side of the meter short of hopping over a protective device, like a fuse, circuit breaker, fusible link, etc.

Thanks I’m going to look into it and definitely do it, I’ll keep my 150 amp and just use an inline fuse to protect the system, maybe 50 amp, unless I install power windows, lol

Just remember that an excess amount of amperage because of high load is far less likely in these cars than a fault to ground. If you're not rockin' with a serious audio system, or jacklighting deer, you're not going to muster over 50 amps of load with headlights and a fan. But if you manage to cause a fault to ground on the charging wire you have both the alternator and the battery to worry about.

Just install a fusible link on the alternator and forget about all this. You are not running a lathe machine or anything. Just don’t install a huge alternator. You will be just fine with the AMP meter wiring as the car is designed. No reason to install a high output alternator.
Blas

What Patrick is saying about safety, and you should read safety as preventing fires that burn your car to the ground, is spot on! The cost and effort to install a voltmeter is nothing compared to what you will experience after a fire. Even Detroit quit using amperage gauges for exactly that reason — fire!

With respect to how much is too much amperage, that depends on your personal power budget for your car. You have to figure it out. My SPF currently has a 240 amp unit, and my power budget has me looking for a 340 amp unit that I can fit in where my current 240 is living.

There is no problem with the SPF wiring handling this. You are charging the battery. The alternator wire goes to the hot post on the starter solenoid, not a cigarette lighter. The various power consumers in your car may or may not require wiring upgrades depending on their individual power consumption.

My fuel pumps running flat out consume 45 amps and have a 10 gauge wire supplying power. My Mk VIII fan used to draw 75 amps on an initial cold start. It used 8 gauge wire. I went to a Focus variable speed fan controller with a soft start feature and went back to normal proletariate wiring sizes.

These cars are custom-built toys architected by their owners — that means guys like us. Just take the time to do it right and, this is really important, if you don't know how to engineer what you are fiddling with buy the expertise from a firm or person who does. It is much cheaper than the whoops that is waiting in ambush for you, just around the corner.

And if I turn every single electrical item on in my car I can get close to about 45 amps. That's my SPAL, my pusher fans and headlights. I don't count my cigarette lighter or horns. I use an AC Delco 60 Amp Generation 1 alternator with a separate voltage regulator that supports both an ammeter and idiot light. The SPAL and pushers did manage to melt a bad connection about 12 years ago. The inductive load, coupled with the increased resistance of a bad connection, created a tremendous amount of heat.

You sized your electrical system exactly right, Patrick. My fuel pumps alone, before I get to anything else, use more power than your car's entire electrical budget. :eek:

Thank for all the info.
I’m just going to install an inline 50 amp fuse with a spare in my glove box and be done with it. I’m over thinking this as usual. I’m too much of a perfectionist at times.

You are playing egg toss with an electrical hand grenade that Detroit stopped using decades ago because of the potential for fire that can consume a vehicle. Be smart and do the smart thing.

You will feel really bad if your car burns down ...

I have a ten amp fuse on my cigarette lighter and it's never blown. And that baby gets red hot with little wisps of smoke coming out of it... so it doesn't take all that much.

Just use a 10 ga wire as the shunt jumper? Any specific length recommended?

10 gauge is fine and all you're doing is bracketing around the ammeter. A couple to three feet should be more than plenty I would think. Now, if you would like to "taste test" your shunt first, just put alligator clips on the end of the shunt wire first and temporarily install it. Then take your car out and observe the behavior of the ammeter as it will be slightly muted as to what you're used to. If it's too muted for your tastes, try a 12 gauge shunt instead.

David,

You are still playing egg toss with an electrical hand grenade that Detroit stopped using decades ago for a good reason! You will feel really bad if the grenade goes off.

So your saying remove the amp meter altogether? With all the original electrics on the SF MKIII (I'm guessing about a 40 amp draw) your saying that's still not be safe? If so why does SF still use them?

When Detroit elected to stop using them, they were using 60 amp or so alternators. Reread Patrick's post #15. That is less than ten amps.

In so far as SPF and their decisions, the best source for why they chose to do what they choose to do is SPF. I have never heard of any replica manufacturer offering to help with any replica with a failed Amp meter that caused a fire and damaged the car. But hey, who knows? You could be the first who does, or you may never have a problem.

Detroit is very cost-conscious, so you can bet they would not introduce an electrical design change unless needed. You may never have an issue, but then again, for $99, you can eliminate the possibility of ever having a problem to start with ...

In the end, it is your car and your call. You need to do what you think is right for you.


p.s. Literally, any fire in that car will cost you more than $99 and the effort to swap gauges.