Alternator Wiring Question
 

I am in the middle of an engine/transmission swap on my 76 Corvette. Additionally, I am adding electric fans (35 amps), FiTech EFI unit (<20 amps), and an electric fuel pump (10 amps). I am trying to wrap my head around a few "loose ends" as I begin to reassemble.


Obviously, this increased electrical load will exceed the capacity of the stock alternator (61 amp), so I have a 140amp alternator to swap in. Reading in other threads, I've seen conflicting recommendations on what wiring needs to be upgraded. Seems a lot of what I read is people upgrading to higher amperage alternators, but not necessarily adding more electrical loads. Will it be necessary for me to replace the positive battery cable to starter, negative battery cable to ground, and/or wire from alternator back to starter?


Any help would be appreciated. The electrical portion of this project is the hardest for me to get a good grasp on, and would rather do it correctly while everything is removed. Thanks!

The system is only going to draw out of the ALT that it needs. In other words at a given time your total electrical load driving down the road may be 10 amps. That is what your ALT is going to put out. This will go up and down depending of what is on. Your new 140 amp ALT will not put 140 amps out all the time so that is no concern. The only thing you might want to look at is the charging circuit wire gauge as it might need to go up a gauge with the higher output ALT because your add-ons will cause more current to be drawn.

Now when you start adding stuff like your fuel pump etc. be sure to use the right gauge wire and don't "tap into" existing wires. Create a power bus bar that is powered directly from the battery or ALT or wire the power side of your add-ons directly from the battery or ALT. This will keep your new current load out of the old factory wiring.

Theandies,

Thanks for the response. Just to make sure I'm understanding correctly, when you refer to the charging wire, that would be the wire from alternator to starter, or something else?

Also, is the power bus bar you mentioned something that can be purchased, or has to be pieced together? If purchased, any chance you could show an example??

I would suggest a larger wire from alt (6 or 8 ga)to battery. Then separate new 8 or 6 ga wire from battery ( add fuse or breaker at the battery in case of short going to a distribution block) then attaching whatever you need to that block with necessary fusses/breakers or relays. You don't need to worry about starter wire size and the electricity will come from the battery instead of the alternator, which is best for handling sudden load demands. Just my $.02. Good luck

It would be the wire going from the ALT to the battery that I would upgrade. That is going to take the full load of your current draw when everything is operating.

You could make a bus bar or buy one to suit your needs.
Something like this:
http://www.jegs.com/images/photos/500/555/555-10522.jpg

Its a waste of time and money routing wires back and forth to the battery.

Run a 6awg from the alternator stud to a terminal block in the engine compartment. Then run another 6awg from the terminal block to the starter solenoid.

Put a 10awg fusible link on the wire at the starter.

There is an original going to the solenoid that you remove. I believe the horn relay is the junction point so probably take it from the solenoid and move it to the new junction block.

Change the ammeter to a voltmeter.

The alternator 'makes power', the battery stores it. Think of the alternator as income and the battery as a bank account.

If the electrical demand is greater than the alternator- the battery should supply the power- that's why going to the battery is the best.

You would not want your house note to come from your paycheck...

Plus the fans usually come on while the vehicle is idling- and at idle the alternator is NOT putting out the rated output.

The battery does more than just start your car- it stabilizes the voltage- reduces spikes AND cleans up the noise- electronics like that.

Look at several manufacturer that say- "connect to the battery" in the instructions.

Here's what I used- Marine stuff- Stainless steel - nice quality for about $20-30 more - well worth it.

https://farm9.staticflickr.com/8735/...3bd4cf02_b.jpg


https://cimg7.ibsrv.net/gimg/www.cor...833eb8a759.jpg

Correct, our old cars essentially run off the battery and the ALT just keeps it topped off as you stated. A car battery can supply much more current than an ALT, as much as 700 to 750 amps (at 12 volts DC of course). That is where the cold cranking amps come in. Unless you have a powerful stereo you won't use that much just driving around and most audiophiles install a separate battery if they are using huge amps.

I'd still think about upgrading the charging wire from the ALT to the battery because now you are introducing more current load on that wire when the battery demands more current. That's what I would do and it can't hurt. If you exceed the capacity of the charging wire it could become a very bad day.

Lol, that big 1awg wire going to the starter solenoid is very capable of supplying any accessory power draws from the battery which a 140A alternator is also capable of supplying.

The run from the battery to the junction block being 2/3rds 1awg and 1\3rd 6awg is less resistance than a 6awg right to the battery.

The couple of feet of 6awg wire runing from the alternator to the terminal block is less resistance than 16' of 6awg wire running to the battery and back.

So, in either case with the alternator or battery supplying the power, the resistance to the accessory power point is less. Less resistance means the power point can provide the required current with less voltage drop.

To sum it up, a 6awg wire connecting at the solenoid does go to the battery. Otherwise the engine would not start.

Any notion that the wire has to run to the battery and then back to that accessory to take advantage of the battery is completely wrong.

Aftermarket accessories say to connect directly to the battery because many people are incapable of supplying the correct connection. It's an easy cover your ass for the manufacturer to say that. For example, I've read about many people hooking a radiator fan to the accessory terminal in the fuse block because they didn't know any better.

I didn't say NOT to do that- I think it a great idea... Just explained the relationship of the alternator and battery in layman's terms.


HUH? :willy:I just showed a picture of a terminal block???

FWIW it's 1/0 gauge not just 1gauge...AKA "one aught"

I was in the automotive aftermarket industry for many years- not just covering our ass- but in thousands of tests- the battery was always the best choice. And you are correct- most consumers aren't as knowledgeable as you.

Richard

What are you trying to act smart about exactly? 1 gauge and 1/0 are both valid wire sizes.

I've always thought the original cable was 1awg. But I checked again and actually believe it might be 2awg. But, I'd bet money the original battery to starter cable is not 1/0.

Connecting the under hood accessory power wire to the heavier gauge battery to starter wire instead of running the lighter gauge all the way to the battery behind the seats WILL provide a better connection to the battery.

Starting in 1981, the first year of the ECM, GM ran the alternator output, both hot and ground together in a separate loom, directly to the battery.

Ummm...sorry I thought you were on a diatribe about the cable in my picture...Factory was 2gu through 71 - and then went to 1gu.

And I'm running a wire from the alternator to the battery just like the BMW I got my engine out of.


:thumbs:

I think you will be overloaded. One summer night in the rain with the AC on will have your car in slow motion. Mr AMP or https://www.dbelectrical.com/alterna...ive/chevrolet/ can get you in the right amperage at idle. Mr AMP is bolt in but expensive. DB has conversion kits to bolt a new style alt from an Escalade to your corvette and they may advise using heavier gauge wire from the Alt to the starter or batt. The good part is you can buy an alternator anywhere when you use the conversion. I have an 82 vette with the fuel injection and I'm running the dual 12inch fans. With a 130amp alt I'm fine while driving but my stock idle is 650rpm. Once my car is hot , headlights on, AC on and wipers on, I'm at 11.9 volts at idle. So when this alt goes, I'll be doing the conversion myself. Good luck:thumbs:

There was a kid on here named DurangoBoy who either made his own conversion or bought it but he documented in a thread very well I remember.

The dual alternator superman?:lol:

I just went thru this on the 81. Ran a #4 hot and ground, just like the stock routing, down and thru the frame rail, out the back, and to that terminal block in the battery compartment. Jambed a 200amp maxi fuse both at the alternator, and in the battery compartment next to that terminal block. 60 amps at idle, and cool as glass.

i didn't quote you post or insult it, but it makes perfect sense that running multiple heavy gauge wires back and forth to the battery is more expensive so it must be better......:thumbs:

If packavette is truly concerned about noise because the connection is not directly to the battery, then the correct answer is to only feed the ECM power from the battery directly. 8' of 12 gauge wire is much cheaper and easier to run from the battey then 20' of 6 gauge wire from alternator to battery and back to engine compartment. The fans and fuel pump and lights sure as hell don't care AT ALL one little bit if there is a wee bit more ripple on their power source.

You have the wrong 130A alternator if it doesn't keep up at idle.

You can get a stock CS144 that will bolt-in and work at idle. Costs about $100 or so. Works better than most of the higher current "beefed up" 10SI case alternators. I just can't recall the application or look up up right now.

The CS144 I have will maintain 14V at idle with fans, lights, EFI etc all running.

Yep- on cost no object cars - when the engineers trumped the bean counters - and the cars go into production with "expensive wire run back and forth" AND it's not even in the sales literature as a selling point- I sort of suspect it IS better....