Alt Replacement Options? A bit confused.

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.

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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...

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.

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

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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.

Tonimus said:

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

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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.

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.

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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.

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.

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.

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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.

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:


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.