2400 watt rms

[Staggian]

Ok I have a 2013 VW Passat S with a stock alternator at 140amps(I think). I am about to put in 3 10” svr skar subwoofer( peak @1600W, rms @800W a piece) in a custom box Tuned at 32hz with a 2500rms mono block amp. I know I’m probably gonna have to replace my alternator but I need to know what size amp alternator I need to replace the stock with? If anyone can give me some info it would be much appreciated.

[Fish Chris]

12 hours ago, Staggian said:

Ok I have a 2013 VW Passat S with a stock alternator at 140amps(I think). I am about to put in 3 10” svr skar subwoofer( peak @1600W, rms @800W a piece) in a custom box Tuned at 32hz with a 2500rms mono block amp. I know I’m probably gonna have to replace my alternator but I need to know what size amp alternator I need to replace the stock with? If anyone can give me some info it would be much appreciated.

Honestly, you wouldn't "have to" replace your alternator. You could always beef your storage way up, with multiple batteries, Lithium, etc. However, being the anti battery, pro alternator kind of guy that I am  lol..... I think if you could find a place to build you a 320 or more amp alt for your car, it would work quite well. I'm running a 2400.1 Wolfram, and a 600 wt 4 ch Skar, with only one group 31 AGM, and a 320 amp alternator, and my voltage is really solid, never dropping below 13.4 or so... even on a hot day. Getting ready to add a bank of super caps, which should help it even more.

[Backwoods]

An extra 100ah in AGM, or 40ah in lithium, AND a 240 amp alternator would be plenty for 2400 watts. But more is always better. You can't have too much amperage from an alt. It will only produce what is asked of it. You can have too much voltage though, depending on the vehicle and amp that you are running.

 

Hell I'm only running a stock 65ah regular lead acid battery right now, waiting on a custom dual battery tray to be build for under my hood before I go dual AGMs.

 

But I also have a 250amp alternator and on 2000rms my lights never dim and voltage never goes below 13.8.  Even on long bass hits it stays around 14 most of the time. Even with the stock 120 amp alternator after installing a PCM bypass to boost voltage my lights never dimmed and voltage stayed about the same, occasionally dipping down to 13.5.

 

But the vehicle matters too, the PCM may limit what voltage your vehicle will charge at even with a HO alternator. An alternator produces amperage. The batteries and vehicle's PCM helps determine what voltage you will really be at. The alternator tries to provide all the current needed for the vehicle while it's running, if it can't produce enough, the system will take the remainder from the batteries. But that causes voltage drop.

 

Volts push, amps do the work, ohms resist, or try and block/reduce, the amps.... 

[markcrnll]

Battery before alternator, always. I've ran a korean 2200 at .5 ohm with a stock battery and 250 amp alternator before and I would be good going down the highway or the road, but as soon as you come to an idle or neutral gear while going full tilt on the music it was mega voltage drop, like 11.5-13 volts almost immediately. So I guess if you don't demo at idle or wire below 1 ohm you could probably get by, probably. Good luck!

[Backwoods]

26 minutes ago, markcrnll said:

Battery before alternator, always. 

MANY people would disagree with that statement. The alternator is the main power source of a system while the vehicle is running. Batteries are secondary, back-ups, to the alternator. But a HO alternator should ALWAYS have the big 3 done with 0 awg ofc to allow the extra current to pass through the electrical system properly.... and have a secondary battery added as well to stiffen voltage to the regulator and keep the alternator from over working. 

 

Also if you have lots of batteries but not enough alternator power for the system AND the vehicle's needs, you will be draining the batteries, which will put the alternator into charge mode more than it should be. An alternator is only designed to charge the minimal drain caused by cranking a vehicle, not charge multiple drained batteries. Charging dead batteries can kill even a new alternator. 

 

There are exceptions. Say you mostly play the system with the vehicle off, and you manually charge your batteries with an external charger, then batteries before alternator makes sense. Or if you are running a smaller system, say 1500rms or less, then just swapping the stock battery for a good quality AGM with a higher reserve capacity should be fine. But any time you add more batteries to charge without adding more amperage to do the charging you are harming the alternator. 

 

I know people who have ran 4K watts on stock alts with just the stock battery for years... But its not ideal, they were really stressing their electrical system and they never got the full potential out of their amp... And at any point they could be stranded with a dead battery and a failed alternator. 

 

 

 

[markcrnll]

1 hour ago, Backwoods said:

MANY people would disagree with that statement. The alternator is the main power source of a system while the vehicle is running. Batteries are secondary, back-ups, to the alternator. But a HO alternator should ALWAYS have the big 3 done with 0 awg ofc to allow the extra current to pass through the electrical system properly.... and have a secondary battery added as well to stiffen voltage to the regulator and keep the alternator from over working. 

 

Also if you have lots of batteries but not enough alternator power for the system AND the vehicle's needs, you will be draining the batteries, which will put the alternator into charge mode more than it should be. An alternator is only designed to charge the minimal drain caused by cranking a vehicle, not charge multiple drained batteries. Charging dead batteries can kill even a new alternator. 

 

There are exceptions. Say you mostly play the system with the vehicle off, and you manually charge your batteries with an external charger, then batteries before alternator makes sense. Or if you are running a smaller system, say 1500rms or less, then just swapping the stock battery for a good quality AGM with a higher reserve capacity should be fine. But any time you add more batteries to charge without adding more amperage to do the charging you are harming the alternator. 

 

I know people who have ran 4K watts on stock alts with just the stock battery for years... But its not ideal, they were really stressing their electrical system and they never got the full potential out of their amp... And at any point they could be stranded with a dead battery and a failed alternator. 

 

 

 

Guess we'll have to agree to disagree... Just speaking from experience. I'd rather be able to demo at idle and you don't get anywhere even close to your maximum amp output from your alternator at idle. Lithium charges at an insane rate. For instance, I'm running a 250 amp alt on 160 aH of JY Power with 2 8k amps wired at .67. My voltage bounces back to nominal within 2-4 seconds after the beat stops, then immediately idles at 25 amp output. Lithium often times never drains even close to half way or even 1/4 of the way 9 times outta 10. Charging a dead agm is a whole different ball game, that will have your alternator charging and working the entire day because of different charging c rate etc. I'll probably catch alot of shit for this last part but you could even run a stock alt on 40 aH of lithium as it will top it off in seconds after the beat drops. But like I said, I've ran high output alt with stock battery and overall I was not happy at all for the reasons I listed, but I got by,  just had to turn the music down every time I came to a stop sign. Self exciting alternators are a different story. You can use the alternator to it's full output even at idle but they are known to creep up into the mid 15s voltage wise which may or may not work well with OEM systems or head units. To be the honest your the first person I've ever heard recommend a high output alt over a spare battery as the first electrical upgrade... I may be wrong though. I look forward to hearing more opinions.

 

[Backwoods]

My opinion.... First electrical upgrade should be big 3, then HO alternator, then extra batteries...

 

But if I'm the only person you've heard say that, that's really weird LoL. I'm an ASE certified technician and I've been through 2 years of auto college... So I'm a little picky with vehicle electrical systems... I've also got my first system back in 1999... First electrical upgraded system in 2004...  But even just a quick Google search will show others that say the same as me... Others that have competed, sold audio gear, and been in the game for decades.

 

I will say I have no real first hand experience with lithium. But still think the alternator is more important. And I'm not the only one.

 

If you Google "car audio battery or alternator first, when to upgrade alternator, charging drained batteries with alternator, most important electrical upgrades for car audio" or any variations of that, I see more people suggesting an alternator first over batteries. Lots of videos, forum post, and Facebook groups with this debate, and there's arguments for both sides, but it seems the majority say alternator is more important...

 

I'd love to read some informed factual posts about why or when a battery for car audio is more important than the alternator if you have links. I'm always willing to learn.

 

[Backwoods]

First picture is my real output of my alternator, tested at varied RPMs.

 

Then my lowest idle RPM.

 

Then my voltage, this was after towards the end of a 45 second 40hz sine wave, also showing volume is up all the way to right before clipping. This is at idle. Sitting at home right now. It's currently 87 degrees.

 

Last my voltage with the system's volume turned down to zero.

 

250 amp alternator, sundown 2k amp at 1 ohm, regular stock panasonic lead acid battery with only 65ah.

 

 

[markcrnll]

Well I'm at work right now but I suppose I would take an auto tech opinion over a car audio enthusiast like myself and if your idle output is as you had posted then I'd opt out for the alternator first also. Thank you for the info Backwoods! Props on the notes!

[Backwoods]

17 minutes ago, markcrnll said:

Well I'm at work right now but I suppose I would take an auto tech opinion over a car audio enthusiast like myself and if your idle output is as you had posted then I'd opt out for the alternator first also. Thank you for the info Backwoods! Props on the notes!

 

No worries man, We are all here to learn from each other, shoot when it comes to building boxes i dont even try and pretend to know anything LOL, but the one thing i do know a little bit about is a vehicles electrical system. I have done a lot of reading and learning and still dont know even half of everything there is to know when it comes to automobiles, or car audio, so i watch as many videos as i can and read as much as i can find before i ever make a purchase. I would of went with a battery first several years ago too, and back in the day i did go with ONLY an extra battery.... I didnt have any issues, but now that i have learned a bit more, id rather play it safer than sorry.