question about HO alternators?

now that i'm getting components for my system, VERY SLOWLY though, i'm trying to figure out how to spend my money most efficiently (seeing how christmas is coming up too). so far i have my head unit and my sub (brahma 12").  i'm probably going to get the Cadence Z9000 amp and an orion amp, as far as speakers i'm looking at mb quarts up front, and infinity 6x9 or something of the like in the rear. i realize that i will need to beef up my electrical system as well. my question is, should i go with an HO alternator or an optima battery? it's all going into a 97 accord if that helps at all. also, i've read that i can take my current alternator to an alternator shop and they can make it an HO alternator. is this true? any ideas on prices? like i said, i'm trying to prioritize here. how many amps should i be looking for from an alternator. on www.4alterstart.com i found an alternator that does like 150 amps. should that be good?

i know there is a whole slew of questions here so any help is greatly appreciated, anything from what i should do in terms of my next purchase all the way to determing how many amps i'm pulling from my alternator. thanks

Start off by figuring the total power of your finished system.  Just as an example, say you will want to have 1000 watts @ 1 ohm, and 440 watts @ 4 ohms.  Use Ohm's Law to determine current:  I = sq rt ( P/R ).  P = 1000 and R = 1 for the first step.  31.62 amps so far...

Then there's 440 watts at 4 ohms:  440 / 4 = 110, the square root of which is 10.5.  Add up the amperage:  31.62 + 10.5 = 42+ amps.  So you would need an alternator capable of providing 42 amps above and beyond what the car needs with all accessories on.

I would start off with a load test of my car's electrical system.  The mechanic will run it in idle with all accessories on and test the alternator output.  He'll let you know how much the alternator has left.  That will tell you what size alternator you need to get, and you can also inquire about rebuilding your current alt to meet the demands you will place on it.  Best bet is to get that bit of business taken care of first, and then you will be in a position to select amplifiers based on a narrower margin of judgement.  That will make the selection process more simplified.

damn, i must say stevdart, along with many other people on this site, you all are pimps. you never cease to amaze me with the knowledge you all have.

thanks for the help

I might have over-simplified the figuring a bit, because I didn't take into account the "peak" power output...just the RMS.  Take a look at specs for the Orion 1200D.  It has outputs of 1200 watts at 1 ohm or 725 watts at a 2 ohm load.  You see that the amp has (3) 40-amp fuses, for a total fuse rating of 120 amps.  If you were to run that amp at 1 ohm, the RMS amperage would be about 35 amps (Ohms Law).  But you see that the amp is capable of 120 amps.  If you were putting 1200 watts into subs at a 1 ohm impedance with that amp, you would have to be the judge as to where to cut off the alternator capability.  That's a huge alternator to add 120 amps plus the fuse rating of your component amp....you might end up with trying to get an alt that will be the sum of: 80 for the car, 120 for the sub amp and 40 for the stereo amp....for a combined 240 amps!

And if you were using that same amp with a 2 ohm load, the power is 725 watts.  The amperage would be much less than what the fuse rating indicates.   For RMS values, compare 35 amps at 1 ohm to 19 amps at 2 ohms, almost half.  To take this to the peak power for a two ohm load, you would need to look at that 120 amps (fuse rating) and divide that almost in half, to maybe 70 amps.

So really, it is a combination of:  what load you will put on the amp, how you will use your system in general, the size and quality of the enclosure and overall install..........as to how many amps the system will demand from the alternator.  So I would consider all this and weigh it against the amp's fuse rating........and find a happy medium.

alright, with that last post stevdart you totally confused me.

here are the components i'm probably going to get, i realize i only need to post the amps because that is what will be drawing the power. i also realize that this is not a post on which amp is better for teh application so, people please don't turn this into one of those.

here's the sub amp i'm looking at. it's a Cadence Z9000 http://www.cadencesound.com/action.lasso?-Database=Products&-Table=WEB&-ResponseAny=amplifiers_detail.html&-token.series=Z&-token.description=&-KeyField=ID&-KeyValue=116&-search. i'd put this amp in mono so it sees 800 watts.

the amp to run the mids and highs is an Orion 4004. http://www.speedsound.com/caraudio.asp?pg=products&specific=jmpmjmpqq. probably run this in 4 ohm load.

now that i'm totally confused, do you think you could help me out again on how to figure out the load here?

Yeah, I had to do that....it sounded too easy.  And we all know nothing is simple in all this, don't we? lol  You just need to find a reasonable middle ground between amperage according to Ohms Law and fuse ratings of the amplifiers.  The Orion 4004 has two fuses 30 amps each for a total of 60 amps.  But you will be using that amplifier in 4 ohm, so the current will be much less than that at the peaks, because the fuse rating indicates what the amplifier can handle at the extreme loads and conditions.  You would find a middle ground for this one between RMS amperage of 7.07 amps and fuse rating of 30.  (You're considering the fuse rating to be 30 instead of 60 because you're only putting a 4 ohm load on the amp, not a 2 ohm load).  Make sense?