Amp Efficiency and wiring

[Amilli]

I am asking with regards to the efficiency of class AB amps. It is said that those amps are only about 50%-60% efficient so does that mean that given a 1000watt RMS Class AB system, my real total output is only 500-600watts ?

I am asking this because my total system RMS is around 1320watts (3 class AB amplifiers all running at 2ohms, yes even the components (full active) are 2ohms each ) 70watts for the tweeters, 200watts for the mids and 780 watts for the sub and my installer said that we can just go with my existing gauge 4 power wires from a previous set-up.

I'm not out to play my system at 3/4 volume for an hour but I usually travel far distances so the stereo will be on for maybe 2-3hours continuously,4 times a week.

What are your thoughts on this because if we need to rewire the power lines to gauge 2 or 0, we would need to change everything from BIG3 to ground wires as well + we have to remove the seats from the car again.

Will gauge 4 be enough

thanks

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[alvitae 10+ year member]

The efficiency refers to how much it draws from your car electrical, If you have a 50% efficient 500 watt amp it's taking 1000 watts from your cars electrical to make that 500. If the math is wrong you get the drift anyway //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Here is a kit that is 4 awg and good for 1600 watts so you would probably get away with 4 gauge.

http://www.sonicelectronix.com/item_13218_Metra+The+InstallBay+AK4.html

 

[n2audio 5,000+ posts]

to build on waht alvitae said.

with a 1300w a/b set up you're going to need 50-55A or so (full volume music) from your alt/batt.

with a 1300w class D set up you'd be more like 40-45A, or about a 20% reduction in current demand.

There's even more difference at moderate volumes because class a/b's efficiency falls as output falls.

So at 1/2 volume you'd be 30A or so a/b and ~20A class D - or a 30% reduction.

 

[pawn man 10+ year member]

to build on waht alvitae said.
with a 1300w a/b set up you're going to need 50-55A or so (full volume music) from your alt/batt.

with a 1300w class D set up you'd be more like 40-45A, or about a 20% reduction in current demand.

There's even more difference at moderate volumes because class a/b's efficiency falls as output falls.

So at 1/2 volume you'd be 30A or so a/b and ~20A class D - or a 30% reduction.

this is wrong i am pretty sure. 1300 watt d class amp will pull at max draw depending on the eff. at least 100 amps of current.

 

[n2audio 5,000+ posts]

I'm talking about real life rms current requirements for amps playing music, you're talking about full volume test tones.

If 1000w amps really drew 100A rms in a car everyone running more than a couple hundred watts would need HO alts and back up batteries.

 

[pawn man 10+ year member]

a 1300 watt rms class d amp is going to pull more than 45 amps playing music.

 

[pawn man 10+ year member]

you put a 50 amp fuse in line on a 1300watt rms amp an see how long it takes to blow.

 

[n2audio 5,000+ posts]

It won't at moderate volume.

It might at high volume -- one could expect short bursts that will pull 100+A which would probably be enough to blow a 50A fuse almost instantaneously.

A simple clamp meter on the power wire would be a lot more interesting to see than at what point a fuse blows given the WIDE range of current vs duration possibilities.

That's not the point anyway.

It seems you fail to understand the concept of RMS current draw.

 

[pawn man 10+ year member]

lol

 

[wu501 10+ year member]

^^you shouldn't laugh because is more correct than you are

 

[n2audio 5,000+ posts]

here's a good informative post from RC at carsound a few years ago.

Someone has asked what they'd need to power a 4kw system. He goes a little overboard saying a stock alternator can handle it, but the principle of crest factor is brought to light...

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

 

[Haunz 10+ year member]

RC dosen't go overboard on anything.. that man tells shit the way it is //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[IDSkoT 5,000+ posts]

Uhh.

Well, OP, this is what you should do...

Add up the size of each fuse on your amp. (It'll have a number ontop of the fuse telling you how many amperes of current it'll take before blowing.)

Now, once you have all of those sizes added up, go here... and round up. If the number your added fuse sizes is close to a certain gauge's maximum chassis wiring, go to the next gauge up.

Everyone on this forum is on 0 (also known as 0/1 AWG) gauge's balls, but if you only need 2, only get two. Unless you plan on upgrading anytime soon.

 

[n2audio 5,000+ posts]

RC dosen't go overboard on anything.. that man tells shit the way it is //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

well, he definitely went overboard in stating "most any stock alternator" is capable of powering a 4000w system.

 

[pawn man 10+ year member]

on 1300 watt rms d class amp average amp draw is going to be more like 65 - 70 amps. and yes, he way overstated when he said you can run a 4000 watt amp on most stock alts. it might run for a while but when the voltage drops below 9.5 volts for long period of time "poof goes the amp" and may take out some subs at the same time. if you run a d class amp at very low voltage it will clip. i would rather overbuild the electrical than take a chance. too much won't hurt a bit(in fact you get alot more out of the system) but, not enough will cost you more in the long run.