not exactly I dont care how large a capacity alternator or battery you use the alternator will only put out WHAT IS NEEDED at a given time. If you have a 90A alternator and it is only having to put out 60A at the moment to keep up with demand then the 120A version UNDER THE SAME EXACT CONDITIONS will also only generate 60A of current.
That is a common misconception; that an alt always puts out max current. not so they only put out max output when they need to and no other time!

 

It's not that easy. The cases are physically different. I have a 136 amp alternator off of the '98 5.9 Ram donor engine and a 90 amp alternator that came stock on my '94 5.2 Dakota. The 136 and 90 both bolt up the same but the center section is a lot wider and takes up more space between the two bolt holes for the higher amp one. On the older 80's alternators you could take a 90 and make it a 120 by adding another rectifier to it and changing the plastic cover. I had it done to the Chrysler alternator on my '88 mini-van.

A.J.

 

let me go in depth to my explanation a tad. the pcm controls the field coils. the effect i was describing is if a field coil should configured to output higher amperage through the same pwm range. if it's way out of skew the pcm can potentially have very short ( you can see them on a oscilloscope most dmm's can't read fast enough to catch it) high voltage spike. when the pcm see's that it will back off the pwm till it drops. they go back and forth really really fast until the pcm figures out XX% of on time will give me 13.8 volts.
i have only seen this maybe two times and it was stupid high output alt's on trucks with stupid big audio amps. it would hit bass and suck the voltage low. the pcm would go full field during the base note. and when the not ended and the amp caps charged again there would be 18 or 19 volts for a split second after the caps charged back up. that is why i suggested a larger batt. it helps provide a reserve cushion and lessen the intensity of the intermittant loads.
anything you can to do smooth the power going into the pcm is worth while. that's why if you open one up and look at it there are caps on the power supply sections. they smooth the peeks and valleys so that sensor readings are something more than just a buzz.


so again i say if you want a bigger alt go for it. they cost though. i have a 120 and i will tell you from checking with my amp clamp that it does charge much more aggresively during hard loads. it's not unreasonable. the battery is big enough that my amp doesn't drain it in an instant. the battery is nothing more than a surge tank. that's it. and my surge tank is big enough that it fills slowely and more controlled even with a bigger pump.


also remember that the pcm does not i repeat does not watch amperage. it watches voltage.
and alts are controlled by 2 states. on and off. the states change very quickly (about 150 times or a second) from off to on. then will stay on for say 100 milli seconds. then back to off. the way this handles it is called pulse width modulation. it does not work like your old gm alt did. they changed resistance to vary voltage to the field. our trucks change pwm. while a dmm will show volts to the field coil lowering a scope would messure that and then show you the waveform that shows it is in fact a digitally controlled 12v pwm ckt.
so in effect. 50% pwm is 50% output (apromatly) even though it's just full out put turned on and off really fast. and 100% pwm is full field. just everything it can manage.


if you need a proof of concept go get your riding mower bat and put it in your truck. you likely have to boost it though. now turn on everything you have and watch the lights flicker. that's voltage fluctuations because the battery (surge tank) is to small. so it runs out of juice then the alt comes on for 13.8 hits it target but also goes past a bit because the battery is small enough that the charge was rapid and the voltage didn't drop in a predictable pattern as the pcm is programmed to see.
you can do the same by have a ground wire that to small or has a poor connection.

 

Also you don't want to run an alternator at max output. You only want to run about 70%-80% of what it's capable of or you'll run it hot and burn it out prematurely. For example, my Dakota with the electric fan, AC on high, and headlights on pulls 90 amps. I have a 136 amp alternator and 70% is 95 amps and 80% is 108 amps. I'm thinking of going to a 150 amp because if I turn my wipers on (which is possible to run AC, lights, & wipers during monsoon season) I might get over the 80% mark. I keep forgetting to test it with ALL the accessories on.

A.J.

 

Once mine goes bad ill step up to atleast a 120. Fine the way it is right now. But if its like everything else it going to tear up soon lol. Life sucks when everything gets in the way lol