Alt Replacement Options? A bit confused.

geocrasher · Dec 12, 2024

Tonimus said:
Just to be clear, I was not advocating the use of one, just that it could be handy in an emergency to get you out of a jam.

And that's how I took it. Being able to "hack" it to get home is a good thing! That got me thinking, it would be good to be able to hotwire most of the vehicle...

Ricko1966 · Dec 12, 2024

If you need to hack an SI all you do is wire terminal 2 to the B+ on the alternator touch term 1 with a test light with the engine running if the light goes out you're charging. Test it occasionally but again this is just to get home so no need to worry.The reason you check occasionally,like next time you need to use the car or its been sitting a while. The alternator needs the exciter circuit( test light) to create an electro magnet and start charging,but the alternator will retain residual magnetism for a short time. And if you sit down with a wiring diaghram,and use common sense you can bypass almost anything on the truck with a piece of wire and a couple alligator clips.

Steelbuddha · Monday at 12:35 PM

Tonimus said:
Summit has a house branded 140 amp 10si pattern alternator. Should be plenty for you. The CS130s are nice, and do go over 200 amps nowadays, but they're also more sensitive. For pure reliability, it's hard to beat a 10/12si. The one I link to is also able to be run as a one wire, so if you're stuck somewhere and need to rig it up, you can.

Summit Racing SUM-810344 Summit Racing™ Alternators | Summit Racing

Free Shipping - Summit Racing™ Alternators with qualifying orders of $109. Shop Alternators and Generators at Summit Racing.

www.summitracing.com

I put that same 10si unit from Summit on my 1984 K20, and the results are great. Very strong charging now, after anemic performance from the stock product.

One important caveat is that you have to upgrade the alternator output wire (i.e. to the battery) to 6-gauge or larger. Anything smaller and you'll melt the insulation off of it.

MikeB · Monday at 1:42 PM

Tonimus said:
Summit has a house branded 140 amp 10si pattern alternator. Should be plenty for you.

The 10SI is alternator designed for 37-63 amp output. Regardless of the internals, the fan and frame cannot handle anything much higher than that, at least not for very long. Maybe you can stuff 140 lbs of garbage into a bag with 63 lb capacity, but it won't turn out well! I see guys doing the math and decide they need 100-140 amp alternators, when a 78 amp 12SI would work for 90% of those applications.

Check out the link below for the correct replacement. The rebuilt ACDelco stuff is first rate, IMO. My truck's 78-amp 12SI is 20+ years old and still working fine. I also have one of their rebuilt permanent magnet starters.

https://parts-catalog.acdelco.com/acesCat.php

Tonimus · Monday at 1:51 PM

MikeB said:
The 10SI is alternator designed for 37-63 amp output. Regardless of the internals, the fan and frame cannot handle anything much higher than that, at least not for very long.

Yes, the 10SI was designed for a max of 63 amps. But modern tech has come a long way since those old regulator designs. Is physically bigger better? Sure. More mass to dissipate heat into. But those modern 140 amp 10SI alternators are usually pretty good. And they don't put out their full rating the vast majority of the time.

Matt69olds · Monday at 5:20 PM

The 78 and 94 amp internally regulated Delco alternators are cheap and easy to find. The 105 and 115 amp CS series alternators are just as common and almost as cheap.

In my opinion, you would have to have a serious sound system or other equipment to need more charging system than 105 amps in a square! Not to mention the Delco alternators are more than likely in stock at any decent parts store regardless of location. The aftermarket stuff, not likely.

PrairieDrifter · Tuesday at 4:47 AM

Matt69olds said:
The 78 and 94 amp internally regulated Delco alternators are cheap and easy to find. The 105 and 115 amp CS series alternators are just as common and almost as cheap.

In my opinion, you would have to have a serious sound system or other equipment to need more charging system than 105 amps in a square! Not to mention the Delco alternators are more than likely in stock at any decent parts store regardless of location. The aftermarket stuff, not likely.

At that point it doesn't matter what you have because what's in stock will also work and bolt right in still, you just don't have the extra output anymore. As long as you can get one for your belt setup.

I went with a Mechman 170 amp unit because it's made in the USA. They say it's a custom housing too, but is a direct replacement for the 10si and 12si. I'd rather underwork something overkill than overwork something mostly all the time.

Doesn't take much sound system to use 170 amps with lights and heater on. My system is more than most have for a daily, only one 15 and a real 1500 watt amp(not no Walmart crap 1500 watts) at basically full tilt it will still dim the headlights a little bit. Of course you should probably be running dual batteries, and for sure proper cables.

Plus everyone is putting lights and sound systems and winch's and electric fuel pumps and all sorts of electrical stuff on their projects these days. 100 amps won't cut it for a good bit of people. Especially a non computer controlled setup, unlike what everyone is used to anymore these days.

geocrasher · Tuesday at 8:37 PM

A HUGE thank you to everyone in this thread! I got the Summit 140A alternator, swapped the pulley, and installed it exactly the same way as the old wiring, and fired it up.

BOOM. The good kind.

14.4V at idle. A quick thank-you video:

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Also, the truck has not idled this well in so long. This alternator must have been on its way out for a long long time! And now that I think of it, the idle has been getting progressively worse the last couple of months. I thought it was due to the cold, but no. It's due to low voltage. I almost wonder if that battery was still good... but it's at 6y/o and I saw 8.25 V on it at one point. It's dead.

Thanks again everyone.

geocrasher · Wednesday at 11:25 PM

Ugh. I am chagrined. I went out to to my burb to replace the 10ga wire going from alt>battery with a 1/0 gauge. Overkill, I know. It was almost free. Anyway, the truck had zero power. Zero. Zeeerrrrooo. Measured voltage on the battery: 0v. Brand new battery. Disconnected the truck battery, and voltage almost immediately jumped to 2v, then almost 3v. Put a jump box on it, got it up to about 12v within a few minutes, but it was clear there was a pretty big draw on the battery. I disconnected the wiring harness from the two terminals on the regulator of the alternator, and the draw stopped. I ended up jumping the truck from another vehicle, and it started right up. The alternator was charging, and so I let it sit for what was goin to be 20 minutes that turned into an hour because I got called away. When I came back, it was charging at 14.4v. It started right up after I shut it down, twice.

Going to check the battery tomorrow morning when it'll be around 25 degrees, and we'll see if it has voltage and if the truck starts.

I clearly misunderstood the nature of this thing and now that I look back on it, when I was tightening the belt, the alternator was clearly magnetized, strongly, so that's where the draw was. I guess I'll be running it as a one wire- one from the harness to the 3/8" lug, one from the 3/8" lug to the battery. Or if somebody else can tell me where I went wrong that'd be great too.

Sometimes the simple things evade me.

Ricko1966 · Wednesday at 11:34 PM

geocrasher said:
Ugh. I am chagrined. I went out to to my burb to replace the 10ga wire going from alt>battery with a 1/0 gauge. Overkill, I know. It was almost free. Anyway, the truck had zero power. Zero. Zeeerrrrooo. Measured voltage on the battery: 0v. Brand new battery. Disconnected the truck battery, and voltage almost immediately jumped to 2v, then almost 3v. Put a jump box on it, got it up to about 12v within a few minutes, but it was clear there was a pretty big draw on the battery. I disconnected the wiring harness from the two terminals on the regulator of the alternator, and the draw stopped. I ended up jumping the truck from another vehicle, and it started right up. The alternator was charging, and so I let it sit for what was goin to be 20 minutes that turned into an hour because I got called away. When I came back, it was charging at 14.4v. It started right up after I shut it down, twice.

Going to check the battery tomorrow morning when it'll be around 25 degrees, and we'll see if it has voltage and if the truck starts.

I clearly misunderstood the nature of this thing and now that I look back on it, when I was tightening the belt, the alternator was clearly magnetized, strongly, so that's where the draw was. I guess I'll be running it as a one wire- one from the harness to the 3/8" lug, one from the 3/8" lug to the battery. Or if somebody else can tell me where I went wrong that'd be great too.

Sometimes the simple things evade me.

What alternator did you go with?Did you change any wiring to install this alternator? If so what? Replacement alternators are very hit and miss as to being good or bad,brand new,right out of the box. If it is 10 si 12 si style wiring, with all three wires on back of alternator disconnected. You should have 1 big wire that reads battery voltage on a meter, a second small lead that shows battery voltage when checked with a meter, a third wire that shows 12 v only when the key is in the run position. That third wire goes to terminal 1 on back of the alternator. The big wire goes on B+ Post on alternator, the other small wire goes to terminal 2. Check that. I'm thinking you have your terminal 1 and terminal 2 wires flipped.

geocrasher · Thursday at 12:33 AM

Ricko1966 said:
What alternator did you go with?Did you change any wiring to install this alternator? If so what? Replacement alternators are very hit and miss as to being good or bad,brand new,right out of the box. If it is 10 si 12 si style wiring all three wire on back of alternator,when disconnected. You should have 1 big wire that reads battery voltage on a meter a second small lead that shows battery voltage when checked with a meter a third wire that shows 12 v only when the key is in the run position. That third wire goes to terminal 1 on back of the alternator. The big wire goes on B+ Post on alternator the other small wire goes to terminal 2. Check that. I'm thinking you have your terminal 1 and terminal 2 wires flipped.

Thank you for the response, ,I'm an idiot. I had them hooked up backwards. I was so sure I had it right, but I just went back and looked at before and after pics.

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Well, at least the mystery is solved. I shouldn't work on stuff when I'm tired. Thanks again.

Ricko1966 · Thursday at 12:43 AM

geocrasher said:
Thank you for the response, ,I'm an idiot. I had them hooked up backwards. I was so sure I had it right, but I just went back and looked at before and after pics.

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Well, at least the mystery is solved. I shouldn't work on stuff when I'm tired. Thanks again.

Go pull term 1 wire,now. Its running 12 volts constant through the field windings,don't know if it will cause damage overnight,do know it will kill your battery.

geocrasher · Thursday at 9:00 AM

I already pulled it by the time I posted. I've got to go out this morning and see if the battery survived the night after taking a full charge.

EDIT: Went out this frosty morning at 19 degrees. Battery measured at 12.87 volts... which is spot on. Connected the wires correctly (they were disconnected) and started the truck, and it charged at 14.66 V. Success!

I also realized the reason I got mixed up on the terminals, but I won't attempt to explain it, it was dumb.

Ricko1966 · Thursday at 11:34 AM

geocrasher said:
I also realized the reason I got mixed up on the terminals, but I won't attempt to explain it, it was dumb.

Was it because your stupid and make bad decisions? Sorry, had to do it.

geocrasher · Thursday at 12:27 PM

HAHAHAHAHA Exactly! So, at first I attempted to follow the "1 wire alternator" install, which *does* have you put the battery wire in 1.

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It didn't seem to charge, so I decided to plug the other wire in to the other side... forgetting that I needed to swap them. It started charging. Then I left it like that overnight, came out to a dead battery, disconnected both wires, got it running (and it charged, since the alternator still had magnetism in it) and the rest you know. Tada. Iterative stupidity.

Alt Replacement Options? A bit confused.

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