If your going to search out something in a higher output, look for Hairpin alternators. Hairpin is a newish way to wind the coils inside.
Your standard alternator has three sets of windings and the hairpin has six to eight. What this means is more output with less heat and the most important part, a huge amount of power at idle.
The problem with getting your stock alternator design to put out more power is, it raises the RPM range where you start to make power. To overcome this, you run a smaller pulley to speed up your alternator. In the case of my TJ, I went from stock 80 amp(?) to 160 by just swapping out the internal windings. Even with the smaller pulley I didn't make power until about 800 RPM ( I idled at 650 ish). I got max output ay 2500 RPM and about 100 amp at 1500. I ran a throttle control to keep the rpm's at 1500 when winching. Some of the standard wound custom "high output" alternators out there wont make max power until 3500 rpm.
Unfortunately no one makes one for my Cruiser so I bought one from a Sequoia to adapt in when I get back from my next trip. The Sequoia can come with a 150 standard, will put out about 30 at idle and max at 2k with a smaller pulley. I picked up a Hairpin 250 amp the other day to add in. With the smaller pulley, it should put out 100-125 at idle and max at 1500 rpm. The only time the higher output will come in handy is winching. Other than that it will be running accessories at idle better.
Most vehicles today have higher output alternators stock and there's really no need to upgrade from that unless you start really modding. The average low battery draws around 40 amp (ish). If your car came with an 80 amp (my Cruiser) your fine with a couple of accessories and the car. You will be pulling about 50-60 amps total. Add in a second battery and your pushing the alternator hard, if the batteries are both low. As long as the alternator doesn't overheat your fine with the lower output. I added a solar panel to keep me topped off when im not driving. This has been my norm up until now.
Now, I have 2 batteries in my Cruiser and 1 in my trailer, a 50 qt fridge in the trailer and a 25 qt in the Cruiser. Think worse case in the 150 amp and up range. At night add in HID lights and I don't have a happy alternator heading home if I let my batteries run low. I have solar on both but, I camp all year round. Clouds, forest shade...means no help there.
Quite a few years ago, I had a small side business building custom high output alternators for people. Finding the higher output parts wasn't easy but I found someone to buy from that wasn't asking a huge amount of money for the parts. My average small case alternator put out around 150amp and my larger 250. I would spend fifty to eighty dollars in parts to upgrade your alternator and charge around 150-180 depending on what I paid for parts using your alternator. The aftermarket cost for the same thing was 400-700 dollars.
The hairpin design wasn't out yet so I made due. My supplier passed away and I was never able to find a supplier to sell me the parts at a reasonable rate. About eight or 10 years ago, I started seeing the hairpin design come out. The parts appear to be very popular with the custom guys and almost all the custom alternators are hairpin now. Again, cant find a supplier for the parts. It would be nice to start building again.
