Stupid-simple alternator upgrade -- 55A to 94A

[rich weyand]

OK, so I got carried away.  First there was the powered subwoofer.  300W, or 25 amps peak draw.  Then there were the Hella 7" round replacement glass with Philips Xtreme Power bulbs.  11 amps.  Then the replacement bumper with the integral fog lamps.  9 amps.  Finally the Flexalite Syclone electric fan.  18 amps run and maybe 30 amps on start-up.

I have been waiting for the 10SI 55 amp alternator to die, and it did.  Lost a diode, I think.  Anyway, it won't lock in at idle any more if even just the headlights are on.  So, time for a replacement, which means time for an upgrade.   

Yes, you can grind brackets and change wiring and change pulleys or go serpentine, and then run the 105 amp CS130.  Or you can just buy a 12SI 94 amp alternator, and swap it out with no other changes.

The one I got is from O'Reilly's.  It's their part number ULT 01-0266.  They stock these all over as they were ubiquitous.  $70 plus a $15 core until you bring the old one in.  It lists as for a 1984 Chevy Camaro with the 305 G-code engine as one example.

One change I did make.  I did not hook up the stock charge wire to the BAT connection on the back of the alternator.  That 12 AWG wire down to the starter is not stout enough for 94 amps.  I cut the connector off the end and put some shrink wrap over the end to keep it out of trouble.  Then I ran a 6 AWG wire from the BAT post on the alternator directly to the battery POS terminal.  I loomed it with the negative battery cable so it's not obtrusive.

Works great.  No more problems keeping voltage lock, even when I am running lots of lights and loud stereo and the cooling fan kicks on.   

Here's a good resource on the 10SI and 12SI alternators.
http://www.madelectrical.com/electricaltech/delcoremy.shtml

[bake74]

     Thanks Rich for the post, this is one that is going into the saved file under alternator upgrades.  Great job.

[rich weyand]

Thanks!  Any time I look into an upgrade or change, and I don't see all the info in one post, or have to scrounge info from all over the net, I figure it's time for a post.  I tend to do quality upgrades that don't require lots of changes, use common parts, and run parts and wiring well within their design envelopes to avoid problems later on.

So I try to write the post I wish I could have found myself, with complete description of the goals, the methods, the part numbers, things to watch out for (like that too-small charge wire), and some reference material -- basically everything you need to go "Hey, I'll just do that" and you can print it out and drag it around with you to the parts store and what-not.

Thanks for the note.  It's nice to get feedback on these posts so I know it's worthwhile to write them!

[dvdswan]

that's awesome.  Thanks for doing the leg work.  I was wondering about an alt upgrade just haven't looked yet.

[rich weyand]

BTW, getting rid of the stock charging wire (BAT on alternator to starter) and replacing it with a 6AWG wire from alternator BAT direct to the battery is a good idea if you are running a lot of electrical equipment on your truck.

If you pull 50 amps through five feet of 12 AWG, you get .4 volts of loss, and heat that wire with 20 watts.  If you pull 75 amps though five feet of 12 AWG, you get .6 volts of loss, and heat that wire with 45 watts!

Three feet of 6 AWG wire from BAT on the alternator to the battery only loses .02 volts at 50 amps, and .03 volts at 75 amps.

[DnStClr]

Thanks for the info, Rich. After reading all that, I feel alternated...

[JustinV]

Just thought that I'd throw another part number in here, I got mine from Napa and their p/n is 13-4356. Direct bolt in, and I believe the old timer behind the counter looked up a '85 buick century with a 3.8. Rated for 94 amps, but the one I got said it tested 110 amps @ 6000 rpm. At idle it spits out 64 amps per the test sheet. 

[bake74]

Just thought that I'd throw another part number in here, I got mine from Napa and their p/n is 13-4356. Direct bolt in, and I believe the old timer behind the counter looked up a '85 buick century with a 3.8. Rated for 94 amps, but the one I got said it tested 110 amps @ 6000 rpm. At idle it spits out 64 amps per the test sheet.

     Perfect, we need more post like this one on the exact subject matters of the threads.  So we can have options, nice contribution.

[Tilt]

This is definitely going in the to do file.  Thanks

[roundhouse]

Nice.   

[fitz]

Great write up, thanks

[75_chevy]

Rich, I am having trouble with my electrical system. I am trying to power two big subs and at night when I have my headlights on and the stereo, the headlights dim drastically.  then when the subs go to hit it draws so much power that the amp shuts off and turns back on. do you think this 94 amp alternator would solve my problem? thanks for your time


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[rich weyand]

If every thing works individually, and then when you have them all on you get problems, yeah, you're running out of juice.  I had the same thing, and this solved it.

[75_chevy]

yup. sweet thanks rich! I'll probably be picking one up today


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[FlatBlack77]

Rich, I am having trouble with my electrical system. I am trying to power two big subs and at night when I have my headlights on and the stereo, the headlights dim drastically.  then when the subs go to hit it draws so much power that the amp shuts off and turns back on. do you think this 94 amp alternator would solve my problem? thanks for your time


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what size amp are you running and are you running a capacitor?