Alternator upgrade question

[bryce6horse]

I just had a complete new a/c system installed this past week and when I turned it on at idle I noticed the volt meter gauge showed charging at 10 but when I turned the a/c off it went back up to 13. I also just purchased a new 5th wheel camper I pull with the truck and when its plugged into the truck it is also charging the battery in the camper. I am thinking of upgrading to a 140 amp alternator. Is there anything I would need to do/add or upgrade after installing the larger amp alternator?

[rich weyand]

What's on it now? And which truck are you talking about?

[bryce6horse]

its on my 86 k20 and has a stock alternator.

[Kaysen]

On my K5 I had a stock alternator and when it finally went bad after years of being overloaded (aftermarket off road lights and speakers with two 12" subs) I bought the biggest one autozone had to offer. The had it in stock, lifetime warranty, bolted on with no modifications, and my lights never dimmed again with the stereo on. I'd go that route again if I needed to upgrade.

[bryce6horse]

i checked with autozone and the largest amp alternator they had was a 93.

[rich weyand]

What should be on there right now is a 12SI 78 amp alternator. The 12SI series has a black plastic turbine-like fan behind the pulley, with a steel front plate, instead of the stamped-fins fan of the 10SI. You can substitute a GM 12SI 94 amp alternator with no changes at all.

To go to a more modern, higher-capacity alternator, like the CS130-style 140 amp alternators, you need an adapter cable, which is available, and probably should upgrade the wire from the output terminal of the alternator to the battery. You also may need to grind the alternator bracket to accommodate the larger unit, and substitute the mounting bolt with one of the correct size, or liberate all the mounting hardware from a later model. Be sure to get one with the V-belt pulley, unless you are also going to convert to a serpentine setup.

Finally, though GM did not make a higher-capacity 12SI series alternator, the aftermarket did. You can get 12SI 140-amp alternators, and not have to change any of the bracketry or wiring. I would upgrade the cable from the BATT output of the alternator to the battery, though. Some 6AWG would be good.

http://www.summitracing.com/parts/pw...FYZAMgodMh4Axg

[bryce6horse]

Rich, actually mine currently has a vbelt for the compressor, vbelt for the power steering pump and a serpentine for the alternator. did the 12SI alternators come with serpentine with the stamped fins? thanks for the link to summit.

[rich weyand]

If it is GM with stamped fins it's a 10SI, the biggest of which was 63 amps. Aftermarket 10SI/12SI replacements come with either kind of fan. From GM, the fan (and amp capacities) were the only difference between the 10SI and 12SI.

Lots of choices in a 12SI serpentine at Summit. JEGs, too, for that matter. I've ordered extensively from both. Customer service at both is exceptional.

http://www.summitracing.com/search/p...ord=ALTERNATOR

http://www.jegs.com/p/Powermaster/Po...rPage=90&pno=1

[willett]

Google powermaster

[bryce6horse]

Thanks again Rich. I also just found out i need to determine if it has a 3, 6, 9, or 12 clock position for the plug and thanks again for the links.

[rich weyand]

You probably also want the mounting ears directly across from each other.

As for clocking, mine took a 3:00 connector position (looking from the back), but you can reclock it yourself if you have an issue. Four bolts hold the back to the front, and you can remove the bolts, rotate the back half of the case, and reinstall the bolts.

[bryce6horse]

here is what it looks like in the truck

[rich weyand]

That's a 3 o'clock 12SI with 180* ears.

[rich weyand]

BTW, when I upgraded my alternator, I removed the red wire from the BATT terminal and replaced it with a 6AWG wire directly from the BATT terminal of the alternator to the battery. Gave a shorter wiring path to the big accessories (electric fan, aftermarket headlights and fog lights, stereo amps) that I have connected to the battery, and gave a heavier gauge wire to handle the added alternator current. I just cut the terminal off the factory wire and put some heat shrink over the end to keep it from shorting to anything.

[bryce6horse]

Rich, what amp alternator did you go up to? I have read where some guys have had problems with the 140 amp do to over heating and burning up in such a small stock casing.

[rich weyand]

I went from a 55-amp 10SI to a 94-amp 12SI.

You wouldn't have to go all the way up to the 140-amp. You could go to 100-amp.

Here's a 100-amp, 10SI/12SI, 180* ears, 3:00 clocking for a hundred bucks.
http://www.summitracing.com/parts/su...make/chevrolet

[bryce6horse]

Thanks again Rich!

[aotte1]

Second Willet, on "Power Master", using PM 150 amp alternator on 1986, C10, exact replacement for original. Mine uses the serpentine belt for the alternator. They also come in different finishes for the case.

[aotte1]

12SI options from PM.

[aotte1]

Hopefully a little better picture.

[aotte1]

A little more info

[bryce6horse]

i picked up a 94 amp alt from auto zone with life time warranty for $69 after i turnned in the core.