brassplyer

I believe my alternator isn't putting out enough juice. The on-board gauge stays well below 13 with the lights on at speed and way down near the warning zone at idle and I've had two batteries go progressively dead.

Running an MSD ignition if it makes a difference. What amp output would you recommend?

Thanks!

REELAV8R

If that's the only extra electrical current you have drawing on the system then I would lean towards your current alternator having a problem if it can't keep up at speed. Likely voltage regulator.

brassplyer

At some point I anticipate getting the A/C running - what would you say a good amperage with plenty of overhead would be?

kossuth

If it’s the OE alternator it’s possibly the 63 amp variant. The MSD only pulls 1 amp per 1000 RPM, not your problem. If you have anything else like electric fans or an electric fuel pump then I would be wondering about your alternators amperage output.

What pulleys are you using? Are you using OE pulleys on everything or are you possibly under driving the alternator.

Probably just a bad regulator as stated in the alternator but figured I would ask for some additional info.

brassplyer

As to which pulley I don't know - I believe it's what came with the dress up set on the ZZ4 which the previous owner installed. In addition to currently not functional A/C I do have electric fans and a currently not functional rear window defroster. The radio I have is nothing special, no big honking amp.

Will a 70 amp alternator be enough when everything is running?

Bikespace

I have a 3-wire, 12si Powermaster, rated to 150 Amps. My electric fans are up to 30 Amps total when running (which isn't often, usually to motion of the car is sufficient)

If you aren't keeping the stock alt for NCRS, why not get one that can handle lots of future upgrades? As long as you do the wiring properly, to accommodate.

REDONBLACK69

First of all, I know little about auto electrics. So take any of my questions for what you think they're worth.
Isn't the function of an alternator to keep the battery charged, not necessarily operate all the accessories on the car?
Should the power and quality of the battery be investigated to see if it's capable of holding enough charge while the car is being driven, and many accessories being operated at the same time.
Just some thoughts.

lionelhutz

Because of the electric cooling fans I would recommend you simply move to a stock replacement CS130 or CS144 alternator. Both have better output at idle to keep up with the fans. You must do some re-wiring to properly support the higher output alternator.

FYI, the 72A 10SI alternator will only output about 20A at idle. You need 2-3 times that current at idle to support those electric cooling fans.

bmotojoe

What Alternator are you running now?
Book says for a 1980 anything between a 37 and 70 amp Alternator was used...
For a replacement, Once you go beyond a 63 amp you jump to the 12si series and the assembly is a little larger.
Not a big difference but a belt size change may be necessary.
I went years ago from a 61 amp on my Late 77 Power Everything to a NEW Delco 80 amp no issues except belt length.

REELAV8R

100 amps will do the trick. 10si or 12si. What you’re really interested in is how many amps it can make at idle.

ive been running a 105 amp 10si for 10 years, electric fans and a/c. A 12si would probably do it easier.

cs130 better yet if you’re comfortable making some wiring changes, not sure what bracketry mods would be needed if any.

brassplyer

The "SI" rating is a new to me parameter.

What kind of wiring changes would potentially be needed to go to a higher amp alternator?

REELAV8R

Larger charge wire for charging system or to the battery lug on the starter is one potential change. If you get the 10si or 12si make sure it's 3 wire not 1 wire version. Your system will plug right into that.

The amperage draw on the system is the important part of whether you need to beef up the wiring or not. If your car is not drawing the amperage then it's fine as is and you will just have more amperage available at idle due to it's higher capacity.
Are the cooling fans wired to the battery lug or the alternator directly?
I can tell you that the 10si is maxed out at 105 amps on mine. It's a bit toasty. Still works but gets nice and hot doing it under the hood of a hot corvette.

an article on the cs130 from 10si conversion.
Also can find lots of threads here on the forum on alternator upgrade if you do a search.
https://www.hemmings.com/stories/art...30-alternators

lionelhutz

SI series is more or less the 1st generation of internally regulated alternators GM used. The CS series is the 2nd generation I think and they applied what they learned from the 1st generation to make an improved alternator. Stock 10SI alternators only go to 72A. The aftermarket has made higher output 10SI versions but the basic design means any alternator using that design lacks the capabilities of the better CS series alternators.

There are AD series alternators that are an even newer design and have better capabilities, but they tend to be rather pricy for the advantages they give.

carriljc

brassplyer

Just go get a 140-amp CS-144. They're a dime a dozen and you can even find one in a boneyard if you need a core....and for that matter, it might be good. That's where I got mine and it cost me like 22 bucks..and that was ages ago.
You can even pick up one of those goofy 3-legged CS-144s and it will work..... those were on tons of those FWD GM cars.
A CS-144 won't be as pricey as an AD and it'll do everything you need.

Why mess around the SI series relics. Just go to CS-144. They're a lot better at idle and pretty much wonderful all around.

brassplyer

Any chance this will be a simple plug 'n play swap from what I assume is an OEM style alt? Should my pointy billet-style pulley fit? Should this be available at a place like O'Reilly?

4-vettes

Nothing that is going to work well is going to be "Plug and play". At the very least you are going to need a larger diameter charge wire. the stock wire I believe is 10 gauge. Once you kick up the amp's this simply won't cut it.
I run a 140 amp Tuff Stuff Alternator. Made in U.S.A.
Available from Summit I know for certain. O Riley's? Not certain.
I had run a 100 amp Alt for several years with my twin electric fans. It was fine. But when I added EFI. now I was running an electric fuel pump and injectors. And it was right on the edge with the lights on and wipers running.
Go to Mad Electricals web site. Go to there tech pages and read up on the differences between 1 wire and 3 wire Alternators and also the needed wiring upgrades.
Whoever put in those electric fans should have upgraded the charging system.
Oh and your assumption that the Alternator is just for charging the battery is incorrect. Everything runs off that Alternator power and what's left over charges the battery is a more correct way of looking at it.

brassplyer

I appreciate the info - I'll definitely check out that site.

It was REDONBLACK69 who pondered if the alternator is just for charging the battery.

4-vettes

Sorry, I stand corrected.
None the less. the tech pages on "Mad Electricals" Web site is worth a read. they are experts on 60's ta early 80's automotive Electrical systems and upgrades.

kossuth

I'd say your marginal at best if not deficient with a 70 amp deal. Generally you want at worst somewhere around a 15-20% reserve on available current. Lets do some rough fuzzy math. Figure electric fans are gonna pull anywhere from 30-40 amps when fully spun up. Your headlights on and on high beam (all 4 lights on) your gonna pull 12 amps just from your headlights. That puts you around 50 amps and that's not factoring in marker lights, wiper motor, blower motor, MSD box, and etc. So figure another 10 amps. That puts you at 60. Granted this is all figuring everything is running full blast. The reserve factor puts you around 72 a amp alternator minimum. Your current system if stock could be right on the threshold. With that said based on the way I see it you should upgrade your system if you have a smaller alternator primary wire and smaller alternator. I personally would step it up to a 100 amp alternator and a 6 awg wire off the back.

brassplyer

Here's what's on it now - can you glean anything as to whether it looks like the wiring has been upgraded from these pics?