Hooking Up 2 More Alternators

What u mean

You are not intending to run it a full output all the time, hence you do not need 5kW "average" to run it. (The design however has to handle the 5kW peak, ie, ~500A.) So what is your expected average power drain? If you can't improve on your previous answer, then yes - you need a 500A alternator for the audio (in addition to the standard one to run the car). Hence inform the 2x 250A alternator builders that they are to be paralleled.

I dont know the peak on the amp all I know it is 4000rms

No, not peak.... We know the max power required by the amp - ie, 5kW RMS (for 4kW RMS output). But you won't be running it at 4kW output all the time... correct? What do you expect it's average power to be - a half, a quarter? Else pick an average power consumption for this design. If you can't decide, or don't know, then I guess you'll have to assume 5kW, hence 500A of alternator as per above (assuming that is enough to recharge and power your system given suitable driving/recharge times with either minimal non-charged usage else lower than full output).

I would like to run it at 4000rms so we will leave iy at 500amps

I did notice an add on the side of my gmail page for stand by generators.

Thread resurrection! So how did this go? Did you get it all figured out? 4000 watts in a daily driver is insane...-Kyle

2006 Mazda 6i

2001 GMC Sierra 2500 HD

No I have not im in the middle of paying for it all bc I have to get a custom bracket and alt for it and its costly

Ref: the insane part, I think some of us decided this was insane back in the first week of December, I'm also pretty sure we are disobeying the laws of thermodynamics, i.e. the conservation of energy. Maybe our first poster should look at the latest Jaguar show car, turbines running at constant revs as a generator for electric motors at the wheels, or the next generation hummers with APUs for the extra electronics in military vehicles.

I have seen quite a few that claim to - else wish to - drive (no pun) a 4kW system. (Yes, RMS output power.) I don't see that as so unusual. Running a 15kW generator, maybe - especially 3-phase and high frequency... But 4kW - no - especially is commercial 4kW amps exist. Nor do I see it as unusual that people follow stupid advice and MERELY get [i]bigger batteries[/i] or just [i]big caps[/i] [u]instead of[/u] a copious alternator to start with - see f.ex good ol' rfhvhtoo's threads [u][URL=https://www.the12volt.com/installbay/forum_posts.asp?tid=124806]charging agm battery[/URL][/u] & [u][URL=https://www.the12volt.com/installbay/forum_posts.asp?tid=125162]relay or isolator[/URL][/u] and where he bought [i]stand-by[/i] AGMs for his 4kW audio (and on floridaspl.com he/they were discussing if a cap stored voltage or current and still refer to the (un-sourced) 100[u]AH[/u] per 1kW "rule")... What [b]is[/b] unusual in this instance is that acetone is starting with a [i]copious[/i] alternator! (IMO - well done! Especially if audio output power depends on input voltage!) Earlier I referred to a system with two 250A alternators, but one fed the main battery, the other fed two AGM batteries for the audio system.   (Though the first "main" alternator could charge all the batteries if the 2nd alternator was not switched in.) As usual in these situations, the cheapest part is the amp. Many reckon batteries are the most expensive part - and that's BEFORE they start replacing them (LOL)! (Then they get caps else wet cells etc...)    Others reckon replacing non-parallelable alternators gets expensive, or simply replacing re-wired alternators which are not capable of withstanding "normal" surges and overloads like purpose-built alternators.