I added after market a/c to my 1975 L48, manual. My question is how much amp output do I need from an alternator? Also I will be adding electric fan setup soon. Thanks in advance for your input.

 

The only additional electrical load I can think of with a/c is the electric clutch for the compressor. That is negligible. The blower fan is the same right? If not it may draw a little more power but not much I imagine.
For the fans it will depend on the fan(s) you choose. 15 amps per fan is not uncommon. 30+ amps for start amperage.
Primarily the problem is idle amperage. The stock alternator will not provide enough amperage too feed the fans and all other electrical at idle.
A 110 amp alternator will do the job. This is what I'm using now and have been for 4+ years. I would go with a three wire set up vs the one wire. It will plug right into your existing system. I think I had to extend the wires on the plug to reach the port on the alternator but that was it as I recall.

http://www.ebay.com/itm/CHROME-ALTER...VVlKad&vxp=mtr

 

It is a newer design and good to 140 amps. Here is a link to read up on.

https://www.corvetteforum.com/forums...version-2.html

There is guidance within to figure out what adapter to use to plug your harness into for plug-and-play (assuming you have a 12 si).

 

I run fans. lights stereos etc and like to have more than I need than not enough the 80's firebird alternator I was using at about 110 amps was borderline on my car so I got a 150 amp, and yes, upgrading the wiring is a must.

This was a while back but I made a post trying to help make up my mind on amps thinking so many people here upgrade this or that but I really got flamed and slapped for going 150, people still just run stock or a little over.

after looking into what most modern cars come stock with I am good with my 150 amps

 

You get flamed alot😭😭

 

I'm using a 100 amp alternator with dual spall fans, no problems

 

Here's a caveat-

The alternator is rated at XXX amps- BUT at what RPM....

"In both ISO 8854 and SAE J 56, alternator testing and labeling standards indicate that the “rated output” an alternator is the amount of current that it is capable of producing at 6,000 RPM."

"When your engine is idling, or really any time it isn’t held at a high RPM, it will only be capable of providing a fraction (sometimes less than half) of that amperage."

Most of time- high current is needed is when the car is idling... sitting in traffic- the fans kick on....as moving down the road the air helps cool - fans kick off...


Here's a typical 140A alternator performance curve-

 

Not as much as you might think , just a few trolls who will follow me to a thread not offer any help but diss me for trying to help
I actually feel badly for those guys,


Back to the threads topic,

The 110 amp 80's firebird alternator I was using must not have been up to par when the Taurus fan was on high, the headlights on, heater and radio on it was straining.....

 

Alternator speed is significantly higher than engine speed.

 

True- but running say a 2:1 or 3:1 pulley ratio- that's still a couple thousand RPM for full output...then you also have to factor in the Alternator's rating is calculated at 70º... not to mention all the stuff connected to it gets hot...

 

According to your chart, that alternator puts out about 100 amps at engine idle. I can't imagine needing more.

 

That's the chart for my Nippondenso... your results may vary...not all curves are the same- because one might be a redhead and one's a blond...

Sort of like saying I have a Chevy 350 and it's got the same HP as ALL 350's at 1000RPM.

You sort of missed my point-

Just because an alternator has a "OGD" (on a good day) 140A rating- pulley size ratios/idle speed/power curve and temperature are also part of the equation.

Richard

 

One of the reasons the old 10SI alternator was replaced with the CS-130 and CS-144 designs was because they were limited in idle current. With electric fans I would highly recommend biting the bullet and going right to the CS144. If you want the newest tech then use a AD244 which is more or less the newer version of a CS144 that fixed the various issues with the CS144.

 

Well I can offer this. My 110 amp alternator puts out enough to show greater than 13 amps (confirmed with a multi-meter to be 13.6 amps) at 700 RPM idle under any condition I have encountered thus far.

Hot, headlights on, A/C on, Dual cooling fans on drawing 15 amps each, stereo on, brake lights on. All of that still falls short of 60 amps. If you wonder if it's going to be adequate add up all the users of power and see what you get. Then get an alternator that is somewhat more than sufficient at idle for that amount of power. In my case the 110 amp 10 SI was more than enough.

I don't think a guy can go wrong upgrading. But to say it is a must is just not true in every case.
I have not done anything to stock wiring.
The fans run off the starter lug connected to the battery. The battery takes the electrical shock for starting the fans. It is more than capable of doing so for two puny 15 amp fans with a total of 50 amps for start amperage. And it could run those fans for an hour or more all by itself if it had to.

The wiring for the charging system is still protected by the fuses it was always protected by. Now if you start having a problem with blowing fuses, you probably have an issue that needs to be resolved. And of course this is assuming the current charging wiring system is in good order.

Modern day cars have significantly higher electrical demands than a 70's era corvette. So it is logical that bigger and better alternators would need to be developed to meet those electrical demands. Just depends on how far a guy wants to go. Sufficient is just that, more is not neccescarily better, and may in fact then require the electrical wiring to be upgraded just to handle the increased potential from a high powered alternator should that alternator be maxed out at some time in the future.

 

The stock wiring on the older C3's passes the charging wire through the firewall connectors twice. The firewall connector uses a decent Packard 56 connector, but they are not capable of handling much over about 50A or 60A without eventually failing and melting down. I wouldn't put a 100A or greater alternator onto that wire with those connectors, but you can if you want.

 

OEM stock alternator for 1977 corvette was 63 amps.
Are you saying even in stock form the connectors could not handle the amperage output of the alternator?

 

New the connectors were just capable of doing it. But, considering that quite a few people have had failures in those connectors, it seems they are marginal at handling even the stock alternator, especially after they have aged 40 years.

 

GM
10DN 1963-72 37-61-amps Externally Regulated
10Si 1969-83 37-63-amps (first internally regulated GM alternator)
12Si 1983-87 56-94-amp
15Si 1982-84 85-105-amp
17Si 1986-90 105 amps
22/22Si 70-160-amp
27Si 1973-85 100-amp
CS 121 61-74-amp
CS 130 1986-97 85-105-amp
CS 130D 1994-up 100-110-amp
CS 144 1986-95 120-124-amp
CS 144 1991-up 108-140-amp (Revised version)

( If the specs are wrong blame the website I grabbed it from )



I took from what he was saying is stock is borderline and over stock is not a good idea...



My alternator is 160 amps and puts out somewhere around 100 amps just off idle where I wanted it,
I have not seen a 100 amp alternator that puts out it's 100 amps at idle, perhaps it's out there.

Seems things that are specific or general upgrades and tech get all mixed together and a bit convoluted and confusing,
I am building specifically a 69 resto mod, some of what I do is specific to that year make and model and my build ideas and some of that tech can be applied to other years makes and models....I do not have the time to outline which is which.

You are comparing apples to oranges saying that in every case the addition of a 160 alternator doesn't need wiring upgrades simply because your 100 amp alternator didn't need wiring upgrades,

It IS true in every case of what I am talking about 1968-1982 corvettes that the stock wiring needs to be upgraded to run a 160 amp alternator,
If you still do not believe that go hook my 160 amp alternator to your stock wiring and lets see what happens.

When I installed the 110 amp alternator on my car I didn't like what seems like a rather dinky gauge wire so I did upgrade the alt wire and ran it to the starter post,
Perhaps 77 has a bigger gauge wire but I get it you do not care you are happy with what you have and I do fully respect that

In my 69 build, more is better for many things, more amps for the alternator, more radiator for cooling more cfm fans for cooling, more HP for fun, better suspension etc.

I didn't mean for that to be all snarky and dbag I just would hate some cat to slap on a higher amp alternator and melt their stock wiring.....

 

I have had a 17SI at some 108 amps on the car BUT driven with a serp drive for years now.....the serp drive is off an '88-91 vette and with dual spals fans a/c, higher output old style lighting, and DPFI and a high energy C4 blower, the thing runs at 13+ volts all the time.....

even at idle under full load.....

 

Why would anyone install a high current alternator but not install wiring capable of handling the max the alternator could put out????

Sounds like faulty logic to me. If there is any fault with the alternator that would drive it to max amps, the wiring would just fry. Oh, if you put a circuit breaker of significantly lower current level than the alternator max, the car would just quit while driving, I guess. Either scenario is a "loser", IMO.

It just makes sense for the 'weak link' NOT to be the wiring. (But, it is your car....)