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Discussion Starter · #1 ·
Asking for a friend that has a 2006 LJ and wants to upgrade the alternator to 160 Amps and replace the stock 90 Amp alternator. Her goto shop says this upgrade will not give any more Amps to the charging system because the 2006 LJ PCM controls the Amps. They claim no matter what alternator Amp upgrade the PCM will only allow 90 Amps:censored:

I looked around the forums and Utube and lots of TJ's and LJ owners have upgraded the alternator and some have upgraded the wire gage to handle it. Did read a couple statements that the PCM is involved with controlling the Amps to the system but nothing that said the PCM wouldn't allow more Amps to be added to the system. Then again I didn't see any proof that more Amps were being charged:unsure:

So seems this shop may have it wrong and we need the wisdom of ROF to confirm that an upgrade to a higher Amp alternator an 06 LJ is going to work. This young lady is trying to set up her LJ for long distance over-landing and is in need of information to get ready for the upcoming travel season. Thanks for your help.
 

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Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to Charging System Operation for additional information.

To put it into easier terms. The pcm does not know or monitor amps. It relies on voltage only. When volts are low it excites the field and the alternator charges. The amount it excites it determines how much the alternator produces. The alternator produces up to its maximum. If you put a higher producing alternator on it will just produce more. 50% of 160 amps is more than 50% of 90 amps.

The only caution is that you want a large battery in good condition or you could charge too fast and boil over a small battery.
 

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Discussion Starter · #3 ·
Thanks rlenglish your knowledge is appreciated. I will pass this on to her.
 

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Not sure what‘s going on now, but about 12 years ago it was all the rage to put a Dodge Durango alternator into our Rubi TJs. I guess it was a direct bolt on.
 

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Discussion Starter · #5 ·
That's correct Norminator, when I had my TJ Rubicon a Durango alternator was on my list of upgrades. The gal with the LJ had that upgrade in mind as well based on fellows with TJ/LJ's in the club. Her shop though said it was not a worthy upgrade!

I sent her rlenglish's info and she in exasperation said she has decided to just upgrade her battery and install a solar panel.

Still I would like to see a before and after, stock TJ/LJ vs 160 Amp Durango alternator, battery charging show down results. It can't all be an illusion:unsure:
 

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The other question she should be asking is "Does it matter?", and what might she be able (or have already) changed to might negate the need. 90A is a lot of power in a vehicle like ours that doesn't have a whole bunch of other electronics. Lights, blower motor, and ... radio? Occasionally the windshield wipers? CB's, air pumps, and things of that sort are all intermittent, and most doesn't use a lot of amperage anyway. A winch does, but that is a reason for a bigger battery, not a bigger alternator.

Changing lights from incandescent to LED is a huge reduction in draw - just changing out the headlights will free up 9A or so and you can free up a couple more by changing interior lights as well (just because there are so many of them).

Not saying a bigger alternator isn't required, just suggesting she think through her draw as well

d-
 

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Biggest advantage I know of fr the bigger alternator, is the quicker power up while slow wheeling in hot weather. I constantly stop the jeep to keep it cool. That plus the radio is on and so is the CB. This is one reason I hate wheeling in big groups, start, stop repeat, really drains the battery quick. A bigger battery helps, but charging it faster is good. I have found that going to a mean green alternator did help.
 

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Totally agree Elwarpo - if you are consistently running the vehicle for short periods of time then you'll need a higher amperage alternator. I don't do much in large groups, so generally don't shut down very often. That used to be a big problem in older vehicles that took a ton of power to even get started - if you ran them for less than an hour you were losing ground relative to your battery charge level.
 
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