I have a 1200RMS amp and a 1200RMS 12" sub. I tested for the DB's and my voltage is getting low as 11.3volts .... IS This a problem... Is it unpowering my amplifier ??? I'm testing my system with the car engine off... So i'm using only the battery... Can it be that the alternator is not charging my battery good ?? I Have an altima yellow top battery.... How can i hold my voltage to 12.3Volts ???
Running that many watts off battery only is certainly not a good thing, but heres why your voltage is dropping like a mofo:
All batteries have a rated internal resistance. Just like your speakers have an ohm rating, so does your battery, its just signifigantly lower. While under normal operation this doesnt take much of an effect, it does when your pulling huge amounts of current.
Lets say you wanted to pull 1200watts from your car's battery. Well, given that a car batter is an array of six 2.1V cells, you have a 12.6V power source. Watts = Volts*Amps 1200 = 12.6*Amps Amps == 95amps.
Now lets figure in your batteries internal resistance (which usualy, when running from an alternator, doesnt have any effect, because power isnt comming from the battery). Lets give your battery an internal resistance of .02 ohms. I dont know the resistance of your battery, you can figure it out thru some math, or you could just call altima, but im going to bet that .02 is fairly close.
we know that : Voltage Dropped = Amps * Resistance Voltage Dropped = (95) * (.02) Voltage Dropped = 1.9V
While .02ohms might not sound like alot, when your pulling 95 amps thru it, we can see that your voltage is going to drop 1.9V. This would bring your 12.6V battery with .02ohms resistance to 10.7V.. sux ehh?
Aside from all the other negative effects of pulling 95amps off a battery continuously (which is a feat, in and of itself, I might add.. im surprise it hasnt gone boom boom yet), we see that internal resistance rears its ugly head and kicks your voltage in its special spot.
Solution: dont run your 1200watts off a battery, its just silly.
If you absolutely have to run it off a battery, get more of them. Competition peeps can get away without dropping too many volts because they have alot of batteries to spread the load around. They arent pulling 100 amps off 1 batt, they may be pulling 10amps of 10 diff batteries, making their voltage drop only .2V
But then, instead of investing a grand for an array of batteries, you could just thump with your car running... something tells me its not going to impact your ability to hear your 1200watt sub very much ANYWAY =)
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So i need batteries for my system to work well .... If i change my alternator to a 150amps would it effect my system ??? and if i add batteries would my system produce more DB's ?
the high output alternator will help when the engine is running the batteries will help when the motor is off. you need to keep stiff voltage rails to avoid damage to the speakers, and to avoid distortion and poor SQ.
a 1200 watt amp will draw up to 120A of current at full output.
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So if i leave my engine running will a 150A alternator put out all the 1200 RMS from my subwoofer ???
yeah a current gen x86 CPU draws around 65+ watts alone.
anyway I'm not familiar with deisels at all, and aside from the glow plugs, and head lamps, I didn't know what else the car may need electrically so figured maybe it is 30A. if it were a gas motor I'd assume a 70A alternator to start.