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Altenator decisions.....help!

6.2Blazer

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The OEM alternator on my '90 K5 finally gave out (thanks to some help from a little mud). After removing the part I found it is the old 12SI style (2 wire plug on back and V-belt pulley) rate at 66 amps, so apparently the 6.2 diesel engines continued to use this style after rest of the trucks went with the CS style. I've owned this truck since '94 when it only had around 40k on the odo and was completely stock, so I'm pretty sure this alternator is original.

Well anyway, a winch is coming this springs so I would like to upgrade from the puny 66 amp. I checked with the normal parts store and biggest common replacement they offer is only 78 amps and I wanted something at least around 100 amps, or higher. With big dual batteries and just occasional winching, I figured 100 amp would be okay.

Here are the options I've found so far:

- buy a specially rebuilt 12SI in 100 amp or more

- adapt to the new CS style alternator (means buying a inexpensive wiring adaptor and possibly minor mods to the bracket)

- install a 1-wire (self-exciting) style alternator

It looks like any of these options could be done for about the same cost.


Any suggestions or comments?????
 

dyeager535

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Whatever you decide, I'd *personally* feel more comfortable using something that is readily available should what happened to you, happen again. /forums/images/graemlins/smile.gif

I don't like the "custom made" alternators for that reason, although for most, the alternator will probably last 10 years. (Although my friend has a powermaster or something that lasted only 2 years or so)
 

6.2Blazer

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I definitely agree with what you are saying, but it shouldn't be a problem since any of the modifications are not really permanent......if the custom alternator goes out I could always slap an OEM back in an emergency.

The nice thing about the 6.2 diesels is that they basically require no electric to run. I ran mine for over 2 hours with the alternator not charging until we got back to the trailer, and then restarted it twice once I got home with no problems.
 

JK5

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I just installed a 140 amp Powermaster Altenator..
a GM copy...so mounting was simple..
89 Amps at idle...
I haven't had a chance to test it yet...

We'll put it to the test this weekend..

On the 100 Amp Altenator you looked at..
what was the amps at idle???
I had a Summit 100 amp...
that didn't have much more than stock. /forums/images/graemlins/whistling.gif
 

Thumper

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Well, there was a post about this a while back. They said there was a stock type (2wire plug, v-belt) availavle on a mid 80s deisel truck that was rated at 120A. The guys didnt know the stock application tho. I have my local parts guys doing some research for me, and he says there was never a GM alternator available that was more than 95A. He says that one is a deisel mid 80s rated for 95A. He cant find any in the book that are higher than that. The only thing i can figure is that he was only looking for the ones that are the small case style. I am going in this weekend and asking him about large case units as well... maybe one of them is 120A. The brackets dont require much of a change to accept the large case style, and supposedly they have the same wiring plug.
Heres the link to the last discussion.
http://coloradok5.com/forums/showflat.php/Cat/0/Number/990599/page/0/view/collapsed/sb/5/o/all/fpart/1/vc/1

Rereading it again, they are talking about a large case 100A unit from a commercial vehicle? But Id still like an application... makes things so much easier!

Mike
 

rjfguitar

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I have a large case commercial altenator and I thought it was a 95amper bt there is a 120?
 

6.2Blazer

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Finally talked to a guy at a shop who sounded like he knew something about alternators. They can rebuild the old 12SI to around 120 amps.....but most of the additional power is only at higher rpms. At idle he said it would only have maybe 25-30 amps which isn't much more than the stock 66 amp version. His recommendation was to upgrade to the large case CS144 style alternator. The 140 amp version they have is supposed to put out at least 85 amps at idle. They sell the brand new Delco 140 amp for $167 and the adaptor harness for $12.95. It is a little more than what I was planning on spending, but there is also no core charge since it's a new alternator which makes it overall cheaper than buying a reman from Napa or Autozone.
 
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