What the equation to figure out amps

 

Silver Member
Username: Matt12490

Benicia, California

Post Number: 393
Registered: May-05
whats the equation so i can figure out how many amps my system is putting out?? I need to know because im going to upgrade my alt. thanks
 

Gold Member
Username: Chaunb3400

Huntsville, Alabama U.S.

Post Number: 5386
Registered: Jul-05
Let's say you install a 1,200 watt amplifier in your ride. Your rides charging system must produce enough electrical current to run the amplifier and still power the rest of the car's electrical requirements. Now how do you know how much current is needed? Simple:
step 1: Find out how much RMS wattage your amplifier will produce based on the load presented by your speakers.
step 2: Divide this number by 12 (volts)
step 3: Take the resulting number and multiply by the factor below, based on the amplifier type:
Class AB: *1.4
Class T or D: *1.2
step 4: Add the totals together if there is more than one amplifier in the system
step 5: add your stock alternator's HOT current rating to this figure.
The total you get is the amount of current your car and audio system will draw at peak output.
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11067
Registered: Dec-03
also listed here if you need it for reference:
http://www.glasswolf.net/caraudio/charging.html
 

Silver Member
Username: N2audio

Lawrence, Ks USA

Post Number: 566
Registered: Mar-04
I would like to inject a little reality into this theory.

Amps don't produce rated rms power when you're listening to musuc. Nowhere near it, not even half of it. If it did - everyone everywhere running 1000w+ on a run-of-the-mill stock electrical system would need a new alt, but they don't. In some cases 2kw will run on a standard elec. system.

The difference between the current draw of music and the current draw of 0dB test tones used for max current draw tests are completely different animals.

I think RC goes a little overboard on this example, but it does help put things in perspective...

QUOTE: Originally posted by Richard Clark:
guys the math is really very siimple------4000 watts is 4000 watts and watts is always volts x amps-----so in a 12 volt system it would be 333 amps and at 15 volts it would be 266 amps--------now if we have to pass that wattage through a lossy system (like an amplifier) we have to account for efficiency losses and add a percentage----ie if the efficiency is 50% we have to double our starting amperage since the voltage is still the same------so a 50% lossy device outputing 4000 watts would draw 8000 watts-------at 13 volts this would be about 615 amps--------class AB amps range about 50-60% at full output and class D amps range about 60-80% at full output------NOW for the biggest factor-------if we are playing music we can automatically divide these numbers by 1/3 or more for short term values due to the crest factor of music and for long term values we can divide by even more-----there are pauses between songs and at the end of the disc where the current demands are VERY low and these affect the long term average quite a bit-----and---sooner or later you are bound to ride by a cop and might have to turn it down a bit-----its not likely that a long term value of more than 10% can be needed for actual power requirements in a real system-------so for that 4000 watt system most any stock alternator will do just fine since it is a rare system that requires more than 50 CONTINUOUS LONG TERM AMPS.............RC
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11082
Registered: Dec-03
true, but I err on the side of caution, knowing the way some people abuse their systems :P
this way you never have to worry about coming up short for power, whether you be playing music and driving to work, or burping the system in a parking lot soundoff.
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