Celica Forums General Discussion Exterior amperage of alternator for sound system

Hey all. I just bought a 600 watt Soundstream amp, and I need to know exactly how much amps the stock gt pulls. Also, How many amps does the alternator have? Please advise! Thanks.

PM ricepowered (darren) he knows

90 amps

^^^ Damn, He's Fast

90amps./. . minus the amps used for ur headlights. . . and all the other electric stuff. . . you have. . not that much . . .

I just went thru all of this. From what I found out, the car when it's running with lights on and all your other accessories pulls 30 amps. leaving 60 amps to spare. Don't take me on this, but that's what the stereo shop that did my stuff figured out. Needless to say I have 2 batteries and an insanely large capacitor to keep everything in check. BTW my research showed the GT has only an 80 amp alternator. Is that right or is it 90?? With just 600 watts, you shouldn't have an issue, it's when you start playing with 1000 plus watts you may want to worry.

Buy a gel battery, and then start fucking with 1000+ watts, like me

BTW I'm buying my second 1000w amp in a few weeks to occomodate my 2 800w 12" subs. do you think I should buy a capacitor?

Carefull, my alternator went out and I was only running streetglow/phone charger/4 interior neons/radar detector.

i ran 800 watts stereo, tv, dvd player, neons, and phone charger on mine for 3 years and never had lights dim or any problems at all

This is a complex subject and there is a lot of confusion about the topic. Fortunately, Ohm's Law can help us out here.
What is the alternator? In car audio terms, it provides the energy to move the speakers in the car. It's output is pulsed DC (Direct Current).
What is the amplifier? Basically it takes the energy from the alternator and changes it to a form useful to move the speakers (Alternating Current). The amplifier cannot produce more average power than the alternator can provide!
If you want to calculate power the formula is this: P(Watts) = E(Voltage) x I(Current) If we want to know how mant Watts our alternator produces we can do it like this:
If you have a 4 cyl car, the stock alternator is typically 70 - 90 Amps and it usually takes 40 - 60 amps to operate a vehicle. So if I have an 80 amp alternator and my car consumes 50 amps to run, I have 30 amps available for the audio system. 12 Volts x 30 Amps = 360 Watts . If we use your system as an example (600 Watts) you're in big trouble... Or are you???
We have to consider our profile as a listener to get a more complete picture. We all fit into three basic prifiles:
10% 'er: Never drives the system to the point of audible distortion. Only listens to well recorded Jazz and New Age. Will use 10% of my amp's power on average. If you are a 10% 'er you would use 60 Watts on average.
20% 'er: Most of the population. Listens to all the popular music recorded today and likes to jam when out on a cruise. They are somewhat familiar what a speaker sounds like when screaming for mercy. They will use 20% of the amplifier's power on average. If you are a 20%, you will use 120 Watts on average.
50% 'er: Total output rules over these folks. The like to try to stretch .50 Cent into a dollar. People in this profile have systems that are off or full volume. They will use 50% of the amp's power on average. If you are a 50% 'er, you would use 300 Watts on average
So you may look at this and figure that as long as I am not abusive, I can put a 600 Watt system like jenn's in my car with the stock charging system. Well, maybe. The one thing we didn't factor in is Amplifer Efficiency.
Amplifiers have an average efficiency of 50%. This means a 200 Watt amplifier needs 400 Watts of input power to produce it's rated output. So the final part goes like this:
(Total RMS power x Profile) x 2
In this case assuming jenn is a 20% 'er would look like this:
(600 Watts x .2) x 2
120 x 2 = 240 Watts
We figured that our stock alternator has 360 Watts to give so jenn based upon 20% listening habbits is OK.
If jenn will be an abuser (50%er):
(600 Watts x .5) x 2
300 x 2 = 600 Watts. The alternator would not be able to keep up with the current demands of the amp in this case.
non-regulated and these amps (like this one) will simply put out all the alternator has to give. In this case 360 Watts. There is really no danger in damaging the alternator with this amp becasue as voltage sags, the curent demand will go down as well. Even if it's a 2000 Watt rated system, it's still bound by the available Watts.
BTW, if the 600 Watt rating is @ 14.4V, than multipy the Wattage by .7 to get in-car power. At 12.5V this amp produces 420 Watts which shuld be no problem with any stock charging system.

Thank you Audio Proffessor JLATD, That was really helpful, I learned a lot from that. so in my case, i have 2 800w subs, running off of a 1000w amp; I will be putting in another 1000w amp pretty soon, in my case should I put a capacitor in also? or would I need another battery to just run the system? or what would I need to do for this to not fry my car?

you will be fine with a 600 watt amp

okay, well, thanks for the info and input.

You're looking at lots of power. I wouldn't say you need to do any of this, but I would strongly suggest it. I would upgrade your alternator for a start. Put in a cap, probably a 1 farad per amp. You don't need them really for speaker amps because of lower current draw, but with bass amps, its a definite plus for that extra power when it hits. It makes a definite difference!

Another battery? Really depends. Like I said, its lots of power. If you like to play your system with the engine off, expect the battery to die after a good half hour (depends on the battery). Try the gel ones, but i'm looking at getting my own separate battery so I wouldn't be stranded after showing off my system to the bros. Just use your judgement.

I really don't want to turn this into an argument because misconceptions on this topic run deep. I am not asking anyone to buy it, just try it on. Remember that I am speaking from the book of Ohm's Law which does not deal in opinion.
All electrical energy in the car ultimately comes from the alternator. Batteries and capacitors are storage devices that need to be recharged. When current demand exceeds the alternator's output, the battery steps in to provide the necessary current. The battery can help only until it's depleted. A "dead" battery may still read 9V.
Bottom line is if we try to bolster the charging system which is not up to the task with batteries, you actually reduce the available energy from the alternator to the system. You will increase the reserve time by perhaps 15 -20 mins per battery, but the system will still hit the wall. When it does, the alternator's duty is now split up even more (has to charge all these extra batteries now).
The number 1 best thing to do would be upgrade your alternator. Extra batteries only really make sense when you have a show car that will play with the engine off.
Capacitors are basically useless because they can never recharge to a voltage higher than what is available. As far as the way they operate, the will do much better on the high frequency amplifiers than they will do on bass amps (spits in the face of conventional wisdom). Save your money for the new alternator fund.
I am not sure what kind of amplifier's you have, but I assume they are unregulated (most are). These type of amplifiers will simply reduce output as voltage drops. This is good news and bad news at the same time. The good news is: the amplifier is very charging system friendly. The bad news is: you won't get the power you paid for. If the power spec number is 14.4V, you are already in the hole 300 Watts at true in-car voltage (12.5V) so you don't want to loose anymore.
If you add another 1000 Watt (14.4V) amplifier you will have a total of 1400 Watts available. If you are an abusive listener, you will need 112 amps of current to produce this kind of power. If you have the same situation jenn has above (stock alt), these two amps cannot produce more AVERAGE power than 360 Watts. This means adding the second amplifier will not make your system any louder than it is now. In fact, if jenn had the same woofer displacement as you do, jenn's system would be just as loud with her 600 Watt amplifier as your's with two 1000 Watt amplifiers.


So if you do everything that is necessary (upgrade power wire, new alternator) your subwoofer system will be +3dB louder than it is now (assuming you have enough current now). If you do not upgrade the alternator, it will look cooler, but there will be no more average output.

Again, not wanting an argument, but the physics and equations have all been worked on by multiple PhD's on the use of capacitors in the power line of a car audio system. If you want to see those details, do a search for them on www.carsound.com [carsound.com], looking at Richard Clark's forum.

Bottom line, capacitors (large ones on your power wire) do nothing for your sound system. They are very good at keeping your headlights from dimming though. So if you do decide to spend your money on one, mount it up front by your headlights where it will do the most good.