Alternators, any difference?
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With what you listed, you wouldn't need an alternator upgrade if you were driving an '85 Civic. 
Not even close!
There's many reasons for why you don't need one.
Before we get into the electrical reasons, let's realize for one that a larger alternator presents an inherently larger drag on your engine, at all RPM's.Effectively, that means you'll lose horsepower, and even fuel efficiency.Also, aftermarket alternators with big numbers can often be misleading...
You might find that a 180a alternator is capable of 180a of current.... at 4000RPM.
You might even find that it's idle current is comparable to your stock alternator.Maybe you've noticed SPL competitors who set up their vehicles with a throttle stop, so they can 'idle' their cars at 3000RPM to make their burp in the lanes?
OK, at any rate, let's look at what we have.
One 1000/1, JL has a 100a fuse at the amp.The other two amps are tiny... we can consider them if you like, but their true current draw is only going to be on the order of 10a - 20a each, or so.A vehicle in operation does not use much current:
Ignition coil - under 10a (usually fused at 10a)Heater - under 10a (and only when in use)A/C and blower - under 20a (and only when in use)Headlamps - under 20a (usually fused at 20a - and only when in use)ECU and engine controls - under 10a (usually fused at 10a)Dashboard - under 20a total (usually under a few fuses)Altogether, that's less than 40a of current during normal operation, and at most less than 90a of current if every gadget in your truck was on at once.
Realistically, these are fuse ratings, not indicators of how much current actually will be drawn - actual current flow will be well lower than the fuse rating, by nature. More realistically, it may be closer to 20a of current during normal operation, up to maybe 60-70a of current draw with every accessory going.So, you have let's say around 40a-80a worth of spare current capacity from your alternator at any given time.
With your amplifiers hooked up and running, bear in mind their current draw is proportional to your volume level... as their output is dependent on your output level.
Their output is also dependent on the recording level of the music...Music is not test tones all recorded at the maximum 0dB reference level... Rather music is recorded with various frequencies occurring not continuously, but occasionally, at various recording volume levels.And consider that like the appliances, your amplifier will not be drawing 100a of current, that's the fuse rating. That means it could draw up to 100a of current before blowing the fuse.
If you are running the amp at absolutely full-bore volume levels, using a track of test tones recorded at the maximum 0dB reference level, THEN your amp might draw 100a of current.However, on real music, it's going to draw less..
First - less, proportional to the level of the tones recorded in the music relative to the 0dB maximum reference recording level.Second - less, proportional to the level you have the volume set to on your head unit. The amp draws current proportional only to what it's outputting to the speakers.Third - less, proportional to the "duty cycle" of the tracks in the music... bass hits, for example... may only exist in the music 25% of the time. Even if they were there at the full recording level, drawing 100a of current each time they hit, this would still make for an amplifier whose average current draw was only 25a - at full bore volume levels, none the less!When you examine what your average current draw is, you would probably be shocked to discover how low it truly is - no matter what music or listening style you have - compared to your amp's fuse ratings. It won't even be close.
Now... let's consider what happens when those 100a surges happen, as the amp makes it's absolute full power for a moment in time, when the bass hits particularly hard - assume the full recording level, full volume.
The amp draws 100a of current from your electrical system for a moment. It'll get it too. No problemo.
Let's say your truck is currently using 50a worth of current because you have your A/C on and are driving.Normally, your stereo isn't drawing more than 50a worth of current,all is well.Then you crank it up when the Beastie Boys "Intergalactic" comes on. Good bass. Booomm.. Booommm..
Each time the bass hits you notice your dashboard lights dim a bit.Surely this must be a problem! No?All that is happening is that when the bass hits, the alternator can only supply most of the current the amp is demanding, but it can't supply all of it, because for that moment in time the alternator's current capacity was exceeded.
The extra current is drawn from your battery, which is obviously permanently installed in parallel as a part of the electrical system.When the bass note stops, current demand drops down to the sub-50a level it was at the moments before the bass note, and all current again comes from the alternator, as the battery recharges the small amount of current it gave up just as quickly as it gave it away.When this happens, the car's voltage inherently will drop from the normal 14.4v level of the alternator, down to the 12v level of the battery - which is why it becomes a source for a moment, rather than a load (it's not really a load, fully charged, either).
Well... it should be simple to see that light bulbs aren't as bright on 12v as they are on 14.4v, and hence you'll notice a small dimming of the dashboard console lights. This isn't harmful, this is your electrical system behaving as it should.
The alternator upgrade is justified when your average current draw exceeds your alternator's current rating. At that point, the battery will be discharging more than it is charging, making it slowly discharge as you drive (at least as long as you have the volume up that high - another factor to consider!).
If you don't drive with the system turned lower for a little while to let the battery catch up, it'll be less charged than when you started the car.And even still - one would have to wonder - with enough power to seemingly justify an alternator upgrade - electrically - if that much power is actually tolerable (much less enjoyable), perhaps there is actually a problem with efficiency somewhere in the system... most likely, more output could be had with less power. The upgrade is a misdiagnosis, rather than the solution to a problem.
So at any rate...
With the mild system you are installing, and the large alternator that your vehicle comes with stock...When you factor down to your average current draw, it will no doubt be lower than even the reserve capacity of your alternator, even with your accessories going.Your money will be better spent on proper power wiring (overkill on the main line to the amps if possible, upgrade the "magic 3", possibly consider installing fast-reacting capacitors to help with the momentary transient where your slow-reacting battery is trying to provide current for that instant where it needs to help out...
And possibly even installing a second battery, IF you find you have some symptoms... such as progressive (as opposed to instantanious) voltage discharge over time as you drive.Those are all good precautions. Installing an upgraded alternator is not a precaution, rather an extreme measure, that often carries the risk of being ineffective for several reasons.And certainly I'd wait until you had some symptoms (and even then trying to analyze the "why?", before justifying such a major measure.
I'll tell you, I have a hell of a lot more power than you do all around, running off a 70a alternator, and a battery that's limited in size to 4" in width... 
All excellent responses!
I've never had a system this big, so I'm trying to set it up right from the get-go. The JL amp is a class D, so I know it's more efficient, but I was afraid with all that current draw (with the amps, the eq's, etc.) that an upgrade in the alternator would be warrented. I do have a cap, but I figured that might be obsolete if doing the alt upgrade.
It's true that I haven't even tried the system out yet, as it hasn't been installed. I guess the first thing to do would be to install the system and get all the proper power and ground wires in place, then test it to see if there would be any headlight dimming and such. Then go from there.
As far as the EcoTech alt, it mentions that it is more efficient and will actually increase fuel milage. This could be a load of bull, but it never hurts to ask 
If anyone else can think of anything to add, please do. You've all been helpful so far, and I thank you for responding.
Para
VEHICLE: 2002 GMC Sonoma ZR2 Alpine CDA-7940 AudioControl EQT x2 JL Audio 1000/1 JL Audio 10W6 (originals) x3 Kicker ZR120 Kicker ZR460 Polk GXR-6 x4 Polk GXR-4 x2Sorry, you can NOT post a reply.
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