[QUOTE]Originally posted by NFRs2000NYC
Ok.....now I see where we're at.

 

If you continue to find mistakes in my math, you're going to wake up with a horse's head in your bed some morning

Yes, stupid me, I pulled a constant current through the whole system when I shoudl have been pulling a constant power Didn't I do something similar with the discussion on speaker power ratings? I think I squared voltage, but not current, or something like that...

 

Sorry Modifry, I didn't realize you were still being sarcastic. I thought is was kind of weird that you wouldn't understand that (especially considering all the electical work you do with the DCI)

Just so I'm clear now. The alternator can put out a maximum of 1500w power. In order to determine if it can handle the amount of power an audio system will put out we take the total RMS watts of the system and multiply it by 1.33, and if the resulting number is less than 1500 than its fine.

So, the maximum rms watts of output our stock alternator could handle is 1500/1.33 = ~ 1125w rms. My one question is that even though our alternator can put out 1500 watts of power, isn't some of that reserved for the electrical system of the car (a/c, headlights, cruise control, etc.)? Or is that the amount left over after all those are accounted for?

Also, how does the different efficiencies of the different class amplifiers work into this? Wouldn't a class D amplifier making 500w have a different effect on an alternator than a class A/B making 500w?

 

The 1500W supply from the alternator is DC, not AC, so rms is an irrelevant term. It supplies 1500W, period. At least 30-40% is reserved for the car, as mentioned before, so you have around 900W of power left to play with.

Efficiency of the amplifier has no effect on the alternator, it only has an effect on how efficiently you use the power being supplied. If your amplifier sinks 300W, but is only 50% efficient, you're only pushing the speakers with 150W of power. A class-D amp in the same situation would pass 270W of that 300W to the speakers.

 

Bob -- i'm on board w/ ya man...

i'm just uber busy at work, so i'm not getting to have any fun...

btw - you can probably also estimate your max current draw by looking at the OEM recommended fusing for each amp. and estimate an average by dividing that by 2.

and Dan,

looking at your last post --
while you're correct -- amps aren't rated on their draw power, but on their speaker side output power... so i would say that Daedelus was correct
there will be a definitely different draw on the alternator for a class D or class AB amp rated for 500 Wrms.

 

I wasn't looking at it from the "rated" power of the amp, I was considering it strictly from the true power pull of the amp on the electrical system.

You say "Potato", I say Spud gun...

 

Alright guys, now that it seems that everyone has come to consensus its time to bring everyone else (including me) up to speed.

Can we all agree on two simple equations (one for an A/B class amp and one for a D class amp) that we can use to determine either in watts or amps the total load on the alternator that can be used to know whether or not the system will run without causing problems? If this is something we can all agree on we could ask bomberman to add it to his S2k Audio FAQ for people to reference.

I appreciate everyone's help and feedback, and their patience helping me with a topic I am not very familiar with.

 

[QUOTE]Originally posted by daedalus
Alright guys, now that it seems that everyone has come to consensus its time to bring everyone else (including me) up to speed.

Can we all agree on two simple equations (one for an A/B class amp and one for a D class amp) that we can use to determine either in watts or amps the total load on the alternator that can be used to know whether or not the system will run without causing problems?

 

I have one of those! On a tripod, with remote ignition.

 

[QUOTE]Originally posted by NFRs2000NYC