Hooking Up 2 More Alternators

I have a 97 golf gti 2.0 and am wanting to know how to hook up 2 more alternaters and leaving the stock one I have a bracket being made for this right but not sure what all I need and how too hook all this up if some one can give me a list of it all and the alternaters I plan on getting are 250amps each and the only battery I have is the stock one if u all need more info let me know ty

Get alternators specifically designed for that purpose (including your original).
You can't just connect alternators together - they might fight each other.


And I suggest a temp monitor for your battery to warn of problems like excessive charge current or collapsed cell(s) etc. A collapsed battery receiving an extra 500A tends to explode quicker than most, but hopefully the shell may heat up fast enough to provide warning. Attached visual alarms could probably state "Brace Yourself!" (assuming a worst-case scenario).


If others know of suitable kits etc, then fine....

So shuld I get a car audio battery for each alternater or just one big one and the alternatersare being hand made and they know what im useing them for I hust dont know how to hook that many up and dont know what all I need

I misread your last as

acetone wrote:

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... and dont know what ... I need

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and I thought "yet you are getting stuff anyhow?!".


So you have three systems - the car and 2 audio systems that will have their own alternator and battery?   I suspect not?


Just tell the manufacturer that you will be connecting them in parallel.
I then recommend that they - with a new battery - be connected separate to the car's electrics except for their common ground.
That's easy to do.
It also ensures independence (so the car will start even with dead audio battery(s). You can even boost the alternator output voltage with some batteries if it's a crap audio that requires higher voltage for optimum output.
You can even charge the audio batteries off the main alternator if the audio alternators are disabled.

Till I read Oldspark's last post all I could think of when I saw this post was WHY?.
Talk about going round the houses!
That is apart from the seemingly impossible task of finding the physical space to mount them.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

You and me and many others I suspect....

I cringe when I see questions like this, but I have been pleasantly surprised by some. Like the first alleged >4kW audio system I read of on this site - but it was!

My last similar involvement this this type of thing began the same way, but again - surprise. But that was 12 months ago, and - not mentioning names of course - but IMO Cezar already had the answers but needed confirmation etc.

But that was an existing system (Dodge) with an added 250A alternator and two AGM batteries. He already intended (or knew) to only common the grounds (phew!). (I'm still intending to check with him, but I assume it went ok. His last question was about triggering the system with some remote...)

That system used the not-yet-patented "Ultimate Intelligent Battery Isolator" system as I so often describe - ie, the battery isolator is merely the cost of a relay of your choosing that can handle the load. (Caveat: Conditions Apply)


Maybe this is an opportunity for someone to sell their cap?
If nothing else, it would allow the alternators to be paralleled (if they each feed through a cap).

In over 30 years around car audio, I've NEVER seen anyone with more than ONE alternator! Why would you want to do this? Who gave you the idea? I've seen some $50,000+ systems at some IASCA competitions and still never seen anyone running more than one alternator, even in systems pumping out several thousand watts.

Get a Capacitor or two and you'll be fine.

kenwood_nut wrote:

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In over 30 years around car audio, I've NEVER seen anyone with more than ONE alternator! Why would you want to do this? Who gave you the idea? I've seen some $50,000+ systems at some IASCA competitions and still never seen anyone running more than one alternator, even in systems pumping out several thousand watts.

Get a Capacitor or two and you'll be fine.

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Im gunna be running 4000w as a daily driver and I dont think my stock 90amp alternater and a capacitor or 2 will work all I want to know is when hooking up 2 more alternaters do u need a battery for each one im new to systems this big so cut me some slack or what do I get to make my 4000w amp run with out any problems ty

"Cut you some slack"? Dude, I'm not dogging you or trying to slam you. I'm only saying I've never heard of running more than one alternator. That's all.

I've run systems with 3 amps with a total of 2000+ watts per channel and never run more than one alternator.

I would just suggest (if you don't wanna use caps) having your alternator upgraded. It's an easy process for any reputable automotive electric rebuilder. Just check your phone book for Starters and/or Alternators, and call one or more of them. Tell them what kind of power you're going to be running and get their suggestions. Ask them if they could upgrade your alternator to hand those power levels. Most can and/or will.

Just keep in mind I'm not trying to slam you or belittle you, I'm only voicing my personal experience based on 35 years around car audio. I'm not a pro installer, but I know several MECP Certified installers who have only been messing with car electronics for a few years. They are "book smart", but I'm more "street smart" (sort of a been there done that kind of thing) than many installers I know.

Let me know what you find out and/or decide. Good luck!

My bad man thought u were being a smart *** its hard to tell when reading I asked some people on hete and the said I would need around 400amps and I was just gunna get 2 250amp alternaters I have talk to a guy who can make me a braket for it all I just dont know whay else I need and nobody gave me any other advice so what u think I should do and agin sry my bad

No prob. Nothing taken wrong. Just wanted to be sure you realized I'm not slamming you, only trying to help.

By the way, this is my last system: two 1,000 watt amps and an 1,800 watt amp. And guess what? ONE stock alternator. I just made sure to get a better battery and run bigger wire gauge and other stuff.

https://s254.photobucket.com/albums/hh100/Hairball98498/98%20Stratus%20stereo/

Mine is 4000rms not max

acetone wrote:

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Mine is 4000rms not max

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Perhaps if you showed pictures and listed brands and model numbers, someone would be able to convince you that you're probably only going to logically get less than HALF of that RMS. Dude, I've seen $10-20,000 systems that didn't have 4,000 watts RMS! What amps are you running? Now you have me wondering. Heck, even the 3 Precision Power amps I'm buying this week aren't going to be anywhere NEAR 4,000 watts RMS. I'm not going to be able to sleep tonight until I know what amps you're running and how many. And to see pictures of your amps at your house (not from the internet) would certainly help us all.

Its in the mail its a autotek 4000.1d rated at 4000rms its bad ass will send pic soon

oh. So you're talking about a Mono Block sub amp that claims to put out 4,000 watts RMS, but that's only if you're running into 1 ohm. That amp isn't even made anymore so I'm guessing you're getting it used. Those amps had tons of problems, which was why they were discontinued. Hope it works for you. But so since that 4,000 watts is only if you're running subs, what are you going to do about your other speakers? Heck, you could run a 10,000 watt amp to your subs but it would NOT be a quality system. Trust me, you're not going to need ANY more alternators just because you run ONE Autotek MM 4000.1D amp. If I could afford ONE Autotek MM 4000.1D amp or even a current model MM 3000.1D amp, I'd rather buy separate realistically-rated amps for front, rear, and subs and still have money left over. If you're one of those who spends all their money on bass but leaves the other full-range speakers alone, you're in for a big surprise.

In my honest opinion, NO ONE single amp on the planet would require more than one alternator.

I give up on this thread. Seems like you're convincing yourself that ONE amp is going to put out so much power that you need to run a bunch of alternators. I've seen 10,000 watt RMS systems than ran ONE alternator. You're only fooling yourself.

Its not s mono block and I have read tons of reviews and no probles iv seen/read have u hurd one before and I have a kenwood amp and head unith as well and I have a jensen headunit wich was way cheaper and its spec r not as good as yhe kenwood but wau better in my opine and not trying to sound mean when I say this but name brand does not mean any thing any more and to honest nothing is better than another its all personal prefence have u ever hurd of hifonics if so the company that makes them make autotek and a bunch others and they r great all made by the same

like I said whay do u recomoned I do then/get

kenwood_nut - 10kW @ 12V - that's an alternator >800A.
Where do you get those?

Even though I am not into "sound systems" per se, I have seen multiple alternators - albeit rare.

But that design I mentioned with an additional 250A alternator to supply the audio IMO is quite acceptable - if not recommended (ie, independence; alternator redundancy etc).


A common large alternator size is 250A, hence a nominal 3,450W or 3600W full output @ 13.8V or 14.4V respectively. IE - probably enough to run 2kW output plus the rest of the vehicle (at reasonable RPM).
But 250A is way short of 4kW running at full output.


Now that I see that acetone isn't one of the usual idiots I deal with (nah - he's a special idiot - jest kidding - pls bear with me...).... eg - RMS is no issue to him - ie, he seems to naturally assume RMS (unlike others).
So I'll trust his situation and that he needs big Amps.

All I'd caution is the difference between a 4kW "true rated" amp at 4kW output (hence maybe ~5kW input) as opposed half-volume with its ~2.5kW input.
That alone HALVES the alternator's power requirement.

And if voltage is not an issue, then it's more a case of suitable batteries. IE - if output is the same at 12V or 11V etc as it is at 14.4V (and IMO it should be!), then he can do like your cited 10kW single alternator systems.   

4000watt system using it daily...not in WESTERN EUROPE matey.
The law would impound your car and in Switzerland arrest you within 5 minutes.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Maybe its for competitions.

Or maybe like me - if anyone ignores my first (two?) warning(s) whilst camping...
Put it this way, I can't action their complaints either - not if I can't hear them. (I know how to Thrash-out the ACDCers et al! Yep - I'm a DRI, but fair.)

Back on page 1 Peter, "I'm gonna (SIC) be running 4000w as a daily driver".

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Ok, maybe he's on a farm....

Or profoundly deaf (and soon will be)**.

I'm just doing my bit to help the industries of the future - sight & hearing. And diet.


** reminds me of an old workplace doc I read - it was a noisy environment but workers "soon get used to that..."!! These days we call that deafness LOL!


But thanks Howard. I may caution, but I usually no longer question beyond a certain point...

Lmao am not going to crank up the volum at 4000rms when driving ok I might every know and then but hell where I live its pretty much a farm lol buy like I have said a million times can some one help me make a list of every thing I would do run this 4000rms system with no problems

The MM 4000.1D is a mono block amp! And what scares me is that such a high output amp is not fan-cooled.

And yes, brand names DO make a difference. I didn't say Autotek was a cheap brand. We could argue about brands for days but that's not what you asked about so I'll back off.

Anyway, back to your 3 alternator question...

Do you really think it's worth all the money and work just to run one amplifier? Dude, you could get 10 times the sound quality with 2 or 3 amps rather than have so much bass nobody ever hears the mids or highs. And if you're hooked on the alternator thing, why not just buy a 250-amp or even 300-amp alternator rather than have more than one? It would be cheaper in the long run and wouldn't take up so much space. And remember, you can have 1 alternator or 10 alternators, but they will only be as good as the power and ground cables hooked up to them.

But if someone told you that amp is not a mono block amp, you might want to get your money back. It is. Just because you can hook 2 speakers up to it doesn't mean it's not a mono amp. It has NO channel separation, meaning it's not a "stereo" amp.

Again, I think you're going to regret all that bass if you don't have any mids or high to compliment the booming. But I see it all the time. I see (and feel) lots of people who go to the local swap meet, buy a pair of 15's and a huge amp, toss it all in the trunk and ride into the sunset. But they leave their full-range speakers hooked up to their head unit with no amps to them, so you hear absolutely NO mids or highs or any kind of clarity.

Good luck, man. I'm sure no matter what you decide, it's gonna shatter your ear drums. And hey, if you can afford to run 2 or 3 alternators and buy subs that can handle the 1-channel output of the MM4000.1D amp, more power to ya (no pun intended, LOL!). I just think there are many other choices instead of multiple alternators.

kenwood_nut wrote:

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Do you really think it's worth all the money and work just to run one amplifier?

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IMO that's an interesting comment on a Forum where people spend heaps....

acetone wrote:

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can some one help me make a list of every thing I would do run this 4000rms system with no problems

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Yep - sure.

For starters I need to know what your average audio power consumption will be....
And what reserve time you want - ie, how many minutes running without charging (ie, engine off).   

And I can answer your last question Peter.
With the single battery it;s going to be about 10seconds before it cooks off!

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Fair go - even my 38AH lasts over minute on my 900A winch!
That should mean 3 minutes minimum at near full 4kW output... (or is it under 2 minutes? Trivia is so forgetful...)

So with a couple of 100AH batteries... though with a separate battery it won't matter (ie, cranking isolation), and with a $25 MW728 else Oatley kit (if the MW728 11.2V is too high for a low-voltage cut-off), even the audio batteries can be protected.

AFAIAConcerned, it's a mere power design issue. I don't care about the audio. (You know my view - I'm happy with the little I have. And if I were to for big quality audio, there is NO WAY I would use a 12V amp! (The amp's remote PSU would sit up front...) Except for camping sites.)

PS - goodnight!

Around no less than 350 amps if im doing it right I took 4000/80%=5000/14=357 and would like 15 but probly asking to much their lol

No - the question was what your average audio power consumption will be....

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.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Thread resurrection!

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

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-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.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

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.

kenwood_nut wrote:

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In over 30 years around car audio, I've NEVER seen anyone with more than ONE alternator! Why would you want to do this? Who gave you the idea? I've seen some $50,000+ systems at some IASCA competitions and still never seen anyone running more than one alternator, even in systems pumping out several thousand watts.

Get a Capacitor or two and you'll be fine.

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Having been around it for 30 years, and IASCA competitions i dont know how you have never seen the bronco built buy Garry Biggs and Alma Gates.  It has won many IASCA events and was very popular with a rediculous amount of publicity since one of the builders was a 70 year old grandma.  It had 12 alternators i believe.  multi alternators has been done, many times.  I have never done it myself so i cannot offer any advice, but here is some proof for you that it can be done. 

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If your cousin is such a good installer, and he will install anything for a 6 pack; why are you talking to me?

I liked....

kenwood_nut wrote:

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Get a Capacitor or two and you'll be fine.

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And that truck has a hell of a lot more underhood room than a Golf, so in the real world.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

If "real" constant-power PSU (SMPS) amps were used, fine - but since all indications are that they or most aren't, I cannot understand why ANYONE would want amps supplied by anything OTHER than the alternator.

Batteries are only for alternator short-falls like low speeds and engine off (plus other changes in load, and filtering).

Caps are only to protect low-ESR batteries (AGMs) and a few rare situations - but NEVER extra or prolonged power. (It reminds me of using batteries/UPS instead of long-term emergency power supplies - misunderstood & expensive!)

Ok I have 2 250amp alt being made what kind and size battery u all think and will last

I think a 12V battery. A 1.2AH should last.

You can figure the capacity yourself. How long do you want it to last at what current? That gives AH or Am (Amp-Hours or Amp-minutes) which you match to the battery.


If that "reserve time" isn't that capacity you are after, then what?
Will a battery last in terms of life span?

A wet cell will, an AGM probably won't. That assumes the amp is a real thumper that stresses the battery(s).
You could add more batteries to reduce that stress, or (as commonly done for AGMs) - add a cap.

But all the above might be academic if you alternator is fast and copious enough, or if your amp is a good design and has a reasonable tank circuit.

Ok thank you ok scince their is going to be 2 more a total of 3 atl shuld I get a battery for each one or just 2 batterys one for stero and one for car or just get 3 one for car and 2 for stero

Yes - it is your decision.
I don't know what you criterion are.

And Peter, another comment about reading this at 6:28am.
Since it's now about 4:30pm where you are what are today's English soccer results going to be?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Soccer? I don't take socker with my coffee.

And yes, I see a time when audio forums should be banned for National Security reasons. I'm starting to recognise the "one battery per amp" and 100AH per kW rules....
Plus the "need lower ESR" but "remove caps for higher peak SPLs" contradictions.
I haven't got the heart to say the "one battery per amp" is "one battery per Amp" not per amplifier, hence 100 batteries for a 1kW output system (based on the 1kW = 100A rule). (I might start another one of Richard's "use a cap - no, I changed my mind" legacies - there are too many already!)

Sorry, it's 18:10 here. I'm dripping sweat from mowing the lawns.

You rotten devil, it's now 7:32 and the frost is still on the ground.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I've posted in this thread twice now and my posts just seem to be dissapearing.

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COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF. PSALMS 37:5

That Darren is because you and I live in the real world where cars go fast, get stuck in traffic, overheat, hit other cars, and none of these home brewed gizmos would last 5 minutes!

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Xmax time Darren, the alternator drive belt went on my late Mits, naturally it was mounted under the serpentine belt that drove the power steering, A/C and water pump. Great in a front wheel drive with about 2" of clearance between the pulleys and the suspension tower.
Wouldn't it be fun with three or more alternators.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

howie ll wrote:

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That Darren is because you and I live in the real world where cars go fast, get stuck in traffic, overheat, hit other cars, and none of these home brewed gizmos would last 5 minutes!

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I agree.

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COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF. PSALMS 37:5

One thing I do like about some modern cars - ONE serpentine belt.
Sure - it breaks and you lose water pump, aircon, alt, power steering and the idler pulley goes quiet....
But it is ONE belt and much easier & quicker to replace (than a "inner" belt).

It might take 2 days figuring out which path to wind it on - but then it is quick. Even quicker next time to match the serp grooves to the grooved pulleys.

I'm considering a serpentine, but that's for alternator only. No power steering etc, and I may convert my water pump to electric (by mounting a motor to the standard pump, AND adding a controller... did I write that I finally fitted a temp switch to my >30 year-old electric radiator cooling fan?).


As to parallel alternators, I like it when they don't tolerate paralleling, or when they (HO alts) are rewound standards that don't tolerate overloads.
The OP with the intended almost 15kW system has the right idea - an AC generator else a single DC generator (alternator).
Then again, why the 'L big amps do NOT split the supply from the output section beat's the 'L out of me!
And with >600V MOSFETs, it's easy running 4 or 8 Ohm speakers again....

kenwood_nut wrote:

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In over 30 years around car audio, I've NEVER seen anyone with more than ONE alternator! Why would you want to do this? Who gave you the idea? I've seen some $50,000+ systems at some IASCA competitions and still never seen anyone running more than one alternator, even in systems pumping out several thousand watts.

Get a Capacitor or two and you'll be fine.

---

I vote this post a classic in entirety and the last line was put so beautifully it just iced the cake.

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COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF. PSALMS 37:5

If the above post dissapears i know something's wrong.

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COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF. PSALMS 37:5

T&T - I recall the above yet cannot find it...

Surely if there were something wrong you'd be notified? (At least after the 2nd time...)



But I like those posts too...
Comparing max peaks to RMS...
Cost to power... (as if cost reflects quality or power!)
And of course the costly ammeter... (I'm sure it has some use...)

Ok got some more money and have talk to a couple of places and I need a custom bracket any one know some one or can help me out iv called and alot of people dont or have no clue where so please help thank you all for your help and advice

Acetone, do you work for the Pentagon on defence procurement, you know redesign the hammer and then buy them sat $1,000 each?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Huh

acetone - do you mean you have the 15kW alternator but can't get a bracket?

O no no no no no I wish that would be the tits I am just getting 2 250amp alt

Sorry - I must be confusing 15kW system. Two in the one year is a bit much.... LOL.

2 x 250 should be ok for 4kW - provided they can be paralleled. (Otherwise, next time maybe.)


Just search for brackets. You know what type of alternators they are.
Or ask those that wound them or that you bought them off.

I presume one fits already, you need to add #2.
I consider that part of the original design - select an alternator that bolts in the easiest. If the serpentine belt is aligned (and the rotation direction is ok (especially if it is mounted - or loops the serpentine - in the opposite direction), then how it bolts on is secondary. Many side-bolt types are easier to mount than the typical pivot types.

I am getting 2 more than the one I already have I talk to a guy he said he make one for around $500 witch seems a lil much trying to find a chepper place or guy

A link I found earlier... Zena - they do 500A etc.

No idea on the price, but rather than having to balance/match for parallel operation....
Better one 500A than 2 parallel 250A.

You can run the 500 or 250+250 separate to the standard alternator; the 500A with its own battery(s).


PS - I just saw that the Zena 250A is over USD$1,000.
Larger outputs are achieved by adding more units with interconnected regulators.
So $500 is cheap for a quality 250A parallelable alternator.

I was reading a while back and was comparing 2 300 and 2 250amp alt and peoole say the 300amp life span is not as good as 250 and I dont know it thats true but if so I have no clue about a 500amp alt but I gunna guess very pricey

That's probably because they are rewound OEM alternators.
The bigger you rewind them, the weaker they are - eg, they do not have a heat inertia so they burn out faster in overload situations.

It's the same with 250A, by 350A will be worse.
Hence why rewinds keep blowing up.

Zena mention similar on their site - see their Powerful alternators for exotic, high current demand, auto sound systems - or was it here here?
Oh well, they mention so much good stuff like needing caps for the faster reacting audio requirement and having floating outputs for those that insist on "absolute ground" etc - they are things that can even be controversial on this site but are ambiguous enough to seem consistent with many audio forums' or users' advice.
But it is a reasonably quick overview of alternators.
And I like their FIVE points (in their Powerful alternators... link - whether #1 that suggest why bigger batteries are or may be needed AS WELL AS a bigger alternator (despite my suggestions otherwise), or ESPECIALLY #3 about needing to "know the peak, minimum, and average power requirements of your stereo system. Without this data you simply cannot properly determine how much alternator capacity that you require."... hmmm - that concept sounds familiar...


Back to larger alternators, overloads etc will get a much stronger reaction, but that is part of the alternator design and should make no difference. There are diode that handle thousands of Amps etc. (I wonder if Bosch have beefed up theirs? )


By the sounds of it, this is another situation where spending less costs more. (Like Born Again batteries, or buying standby batteries instead of cyclic...)