Why our Jeep JK Needed an Alternator Upgrade
Our 2012 Jeep JK Unlimited Rubicon is set up as a camper, and is loaded with electrical accessories. Like most that do any serious off-roading, we run a winch. In our case that's a big 12,000 lb Warn unit. We also have a fairly significant amount of lighting with 21 Baja Designs lights tucked into various spots all over the Jeep. While these two loads are big, what really drove this modification was our 2,000 Watt pure sine inverter. We installed that to run things like a hair dryer, electric Kettle, Microwave, etc. At idle, we observed a max output of 123 amps while using big appliances like that, and it would drag the voltage down to around 12.2. Increasing engine speed could help, but so could a bigger alternator. This sent us hunting for the perfect Jeep JK alternator upgrade for our rig.
Selecting the right Alternator Upgrade for the Jeep JK
When we first set out to find a higher output alternator, we were met with TONS of options from shops selling alternators with all kinds of claims - most of them not terribly trustworthy. We wanted something as reliable as possible that would produce higher output, especially at idle. This would allow us to run some of the bigger loads without forcing the Jeep to high-idle.
Imagine our surprise when we found, after a bit of research, that Jeep installed a massive 240A unit on some Gladiators from the factory that might bolt up to our older 3.6! This sounded almost too good to be true, but the payoff would be huge if it was. We dug into the details, then finally bit the bullet and bought one. When it showed up, we took these comparison photos before installing it in our Jeep:
The new unit was definitely bigger and heavier than the stock alternator, but shared all the same mounting dimensions. We weighed them both out of curiosity, and found the 240A alternator to be 4.4 lbs heavier than the original 160A unit - not that weight matters much.
Installing the Alternator Upgrade in our Jeep
With the comparison out of the way, we went ahead and installed the alternator. It literally bolts right up, just like the factory unit does, without any modifications! This makes this a simple R&R job that can be completed very easily.
After installing it - we can confidently say that the MOPAR 56029803AA alternator is indeed the answer we were looking for. While we opted for genuine MOPAR, there are much cheaper options available, like this one. While it does bolt right up, we didn't want to rely on the small factory wiring alone to connect this beast to the batteries, so we came up with something better.
Upgrading the wiring from the alternator
We decided the simplest thing to do would be to parallel the factory positive wire with a big fused connection at the battery and then parallel the ground as well. While there are kits like this, we simply assembled the red wire using these cables/Lugs using this crimper and then bolted this fuse block to the battery terminal with this fuse.
For the additional ground conductor, we assembled it the same way, just with black wire and no fuse. We ran it to the bottom of the alternator and over to the big ground distribution bar we have on our Genesis dual battery kit. In a normal application we would have just landed it with the battery negative terminal.
How the JK Alternator Upgrade performs
With the new alternator installed, we did some testing and found that the same load that would drag the voltage down to 12.2 would now have no effect at all. The Jeep happily holds on at 14.2 under identical conditions almost like we didn't have the 1,800W hair dryer running. I also tossed the meter on the output wire just like before and found the output at 141.1A - a big step up from the 123.2 the smaller unit could produce at idle. I never did run more loads to see how much current it could muster at idle before the voltage would dip, and may test that in the future just to satisfy curiosity.
Final Thoughts
We have been running this upgraded alternator on our JK now for two years (installed Feb. 2024), and it has proven to be everything we hoped for. There have been no reliability issues, though that is not a surprise with this being a genuine MOPAR alternator. I sure is nice to have stable voltage at idle despite some pretty serious electrical loads. I suppose the winch would drag the voltage down as that load is MASSIVE, but I've never measured it.
To be transparent as possible, I want to add that we bought all these parts at full retail from various suppliers. Also, we will earn some commission if you buy through one of our provided links. If you found this information useful, and want to help us out, click a link on this page to shop and we'll earn a couple percent. This does not affect the price you pay, and we greatly appreciate it! In fact, any shopping through our affiliate links, like this one to Amazon.com, and this one for Summit Racing, works the same way. For the full affiliate disclosure and vendor list, click here. I wish you the best of luck with your project - Thanks for visiting!
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