Re: The right alternator
Add it up. Normally a Jeep alternator is about 35 amps or so. It's adaquate as long as you don't have lots of accessories. A stock electrical system will draw about 20-25 amps with everything turned on. Whatever is "left over" goes to recharging the battery - IF the battery needs it. Otherwise the overage is not used.
Add it up.
Take the wattage and divide it by the volts
W/V = A 55W / 12V = 4.5A
Many driving/fog lites are 55 watts each = 4.5 amps each - allow 10 amps for a pair.
Big high intensity lites may be 10 each.
Stereos, amps etc draw heavy only on peaks, but look at the labels.
Allow 2 amps for your CB.
Winch? The alternator cannot keep up with a winch anyway - it will mainly serve to recharge the battery. A bigger alternator will help the battery recover faster, and it can help supply SOME of the power to the winch during use -- so big ones are helpful there.
THE MAXIMUM A BATTERY CAN STAND TO RECHARGE IS ABOUT 30 AMPS! More than that will kill it anyway -- that's why most automotive ammeters only go up to 30 amps. Too much charging current warps the plates.
So -- take the stock amount of 25 circuit draw, add up your accessories, add a few extra amps as a margin, then add 30 to that to charge the battery if it needs it. That's the most your rig needs. More capacity just goes to waste.
Remember -- the alternator supplies all the accessories and engine FIRST, then whatever is available can go to the battery - up to that 30 amps.
To get a battery to take more than 30 amps the charging voltage has to go way up - 18-20 volts? The battery has internal resistance that limits the current in -- Ohm's law. But 20 volts is very hard on lites, modules, and electronics.
You can measure that internal battery resistance. Put an ammeter in series with the battery cable on a low charged battery. Read the voltage at the terminals and the current going in. Use Ohm's law R=V/A.
Works for charging or discharging.
Then once you know the resistance, you can calculate how much voltage is needed to charge it with higher amps.
The voltage regulator prevents that over-voltage, thus overcharging, from happening.
Now if you are planning to share it as a dual purpose welder, go as big as you can get for the money.