Hi to all,


This is all Information I myself have gathered from the MECP Installers Guide book.

Alright Here's the Question!

I am trying to figure out how much pull on my alternator I am getting from the amp.

Here is the formula We use to figure this out


I = (Po - n*Po + Po) / V

Now

I = amperes
Po=RMS
n=efficiency
V=voltage

So for me its:

I = (3000 - .8*3000 + 3000) / 13.8

So I do this

3000*.8 and i get 2400


3000-2400=600

600+3000

3600/13.8

260.87 This is my amperage draw correct?



and if I'm correct for everyone else heres an easier equation for this:

I = (2-n)Po/V


So for me this would go

1. 2-.8 =1.2

2. 1.2*3000=3600

3. 3600/13.8

And there we go. 260.87!!!!!


Now, We must remember that Most Class D Amplifiers have a 80% Efficiency Rating and Most Class A/B Amplifiers have a 60-70% efficiency Rating!

 

Interesting but way over my head bump for ya!

 

Well im not sure about that considering there are a vast range of alternators out there and for the most part guys use stock and if your math is correct then its pullin every bit of amperage it is making.....and u say tour using just this one amp. and i run 3 on my stock alt. with no problems. They r not small by any means two class D and one for mids highs. Im sure someone can chime in for u though, im not sure if your asking if this ok to run or jus tryin to stump 99% of people on here with some fancy math.

 

...new to site... but just reading up on various threads...

To the OP, without checking your SPECIFIC case and math, I'd also mention that the calculations presented are likely based on MAX or PEAK DRAW conditions, hence, NOT representative of constant draw characteristics in real-world usage. So long as you are not drawing MORE than the Alternator is rated at CONTINUOUSLY for EXTENDED periods, the BATTERY will suffice for the peak transients of current draw (like a "filter" to mitigate the affect on the alternator) and then the alt. will "refill" the "reservoir" of the battery accordingly.

Large capacitors work similarly on a SHORT CYCLE basis (instances of musical transient that draw PEAKS form amps... such as SUBS would require...) and/or secondary batteries can be more stable as well.


Don't know if that helps anyone out there... but to the point of the later post, you MAY well run MULTIPLE amps that EACH have the potential to draw at or near the limit of an alternator, but combined in real usage, seldom if ever will.


My $0.02...


Carry on...


EDIT: I went back through the OP's math and logic... and I don't quite get it now. I suspect an easier "short cut" would be to look at your amps max. rating (usually AT or just below the FUSED RATING... i.e.: 20A or 30A fuse for moderate sized amp...) then add up all your amps i.e.: 1ampX15A rated + 2ampsX30A rated = 3 amps totaling a PEAK CURRENT DRAW of 15+30+30= 75A. Knowing that if ALL the amps actually DRAW that level, you'd likely be blowing fuses... they are likely WELL BELOW that current draw. Now, consider that it's your BATTERY that supplies the current to the amps, and the alt. that feeds the battery... you should be FINE most of the time UNLESS you are drawing CONSTANT CURRENT LEVELS that exceed the alternators ability to supply. Even THEN you are only going to begin to deplete the BATTERY faster than the alternator can replenish... and would require constant running of peak levels of current draw without a break and opportunity to replenish the battery, right?

Anyway... unless you are into MEGA watt/current drawing multi-amp setups... in which case bigger current alternators MIGHT be warranted... you usually don't need to worry about a basic multi-amp setup. Even then, a second battery is often enlisted to address this issue. Other considerations are, if you use a high-power stereo with your engine OFF for extended periods... you may deplete a battery rapidly...

Just some second thoughts...



-crisp

 

Couldn't you just hook a VAT40 machine up to the battery with the inductive pickup going to the alt, then fire up the amp and see how many amps it draws? As mentioned, it can't be drawing more than the fuse that's protecting that circuit or it would be blowing the fuse...