I am wondering what the specs are on the stock alternator like total output and at what RPM. Also what is the output at idle? I was also wondering what an average is for a JK that is just running with no lights, a/c fans, or anything else running besides the engine?

 

Do you suspect yours is about to die, looking to upgrade, looking for interchangeable options, or just curious?

Pulled from my 2010 'potential buyer guide', it's rated at 140amps but I don't have a number on the RPM where they measure. The mean green upgrade (1388) is a 220 amp.

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I already have an upgrade but have not installed it yet. I was just wondering what the stock specs are. I would be surprised if the stock unit put out 140a.

 

I just read online where the stocker is rated for 40-60 amps. Where did you get this 140 figure?

 

I have three different spec sheets that came from my dealer that states I have a 140a alternator. Took my rig to a shop to add an optima battery and they checked my alternator and confirmed it's rated at 140a
Augi

 

Ok scratch that, that was info on the quadratec website and was a typo. They meant 140 - 160 amps. I have a 240a mechman unit waiting to go in.

 

It should say right on a plate on the alternator itself. Those are pretty accurate figures. Say the stock alt puts out 140, a running JK without accessories uses roughly 80 amps, you're left with a surplus of about 60 amps which sounds like the number you found online.

 

My window sticker states 160 amp alternator. 2012 JKUS.

Side note: most alternators put their max power out at around 2000 rpm.

 

The link below takes you to rockauto.com and shows the output curve on the stock alternator, it should give you an idea of what to expect from yours.

http://www.rockauto.com/catalog/moreinfo.php?pk=2140808

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An alternator upgrade is all good, but if the new one has, say, 80 or 100 amps more output than stock, the cables should be upgraded too.

The stock cable appears to be 6 gauge, rated for around 120 amps. I'd want at least 4 gauge and preferably 2 gauge for a 200 to 250 amp alternator. This applies to the ground cables too.

Without upgrading the cables, two things happen: First, some of the power is lost in the too-small cable. Second and most important, the cable may run hot which is a fire hazard.