# MKIV second battery or alternator upgrade?



## BIGPIMPNfshtx (Mar 20, 2008)

has anyone upgraded their power with a second battery or higher output alternator?looking for a diy.








* stock alternator is 90A and my amps alone can pull 180A.


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## jokers10 (Sep 11, 2011)

I haven't done it yet, but I plan on it. If you get the right alternator, it will fit like factory. It will require removing the front bumper, and putting the radiator in the service position, but should take less than a day if you have done that before. 

No need to install a second battery before this, because it will just cause more stress on the stock alternator. Best bet if you don't have the money for a $600 alternator, would be to upgrade the stock battery to an AGM style battery from XS Power.


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## NFrazier (Jul 22, 2006)

jokers10 said:


> I haven't done it yet, but I plan on it. If you get the right alternator, it will fit like factory. It will require removing the front bumper, and putting the radiator in the service position, but should take less than a day if you have done that before.
> 
> No need to install a second battery before this, because it will just cause more stress on the stock alternator. Best bet if you don't have the money for a $600 alternator, would be to upgrade the stock battery to an AGM style battery from XS Power.


A secondary battery is really designed for if you plan on running the system without the car running often (in which case you'd get a agm, deep cycle battery such as Optima, Kinetik, XS Power, etc.).

Upgrading the alternator is for when you have an overall lack of current. The factory alternator is designed to run at 80% duty cycle when all of the power needed to run everything in the car is on.

Do some math, find out what your factory alternator is designed to have for your car to run, find out how much current your added equipment will need (take into consideration the duty cycle/dynamics of music - that is regular listening music is at about a 25% duty cycle) and get an appropriate alternator.

I've replaced my alternator with a DC Power SPX300. 320A max, 220A at TRUE idle (800 rpm). That alternator is $700 but they do have other alternators depending on the needs of your setup.


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## BIGPIMPNfshtx (Mar 20, 2008)

Just had my mind blown. the oem alternator for my jetta is 90A. My two amps alone can require 180A. My cars electrical I understand requires about 70A. I definitely can't spend a G on an alternator but I will spend a few hundred. I just upgraded to a yellow top optima n I'm one cable short on finishing the big three. I was reading on swapping a passat 150a alternator to give me a bit more breathing room but I'm not sure if that's any better than just adding a second deep cycle. 

Advise?:banghead:


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## RonPopeil (Apr 26, 2012)

drawing that much, you'll need a new alt. the battery would just be a bandaid as the alt won't be able to keep up and charge the second battery. 

why are you drawing so much? powering subs on AB amps? if i were you i'd look at my amp situation and try to find a way to bring your draw down. there's no way you can add 180amps of draw without an upgraded alt.

the 150amp alt will def help. a second battery won't. no matter how many batteries you have you need an alt to charge them.


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## BIGPIMPNfshtx (Mar 20, 2008)

I'd have to double check on the class Ive had them since 2005. I'm 99% sure the sub amp is a D amp. I saw this video on power http://www.youtube.com/watch?v=5Ckuc2dfVV4&sns=em that's how I got to thinking about power. He says to add up the fuses n that will give you a basic idea of how much power you need.

If I just upgrade the alternator n use the yellow top by itself, will there be an over charge problem between the HO alt n the yellow top when I'm not BASSin' out?


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## NFrazier (Jul 22, 2006)

BIGPIMPNfshtx said:


> Just had my mind blown. the oem alternator for my jetta is 90A. My two amps alone can require 180A. My cars electrical I understand requires about 70A. I definitely can't spend a G on an alternator but I will spend a few hundred. I just upgraded to a yellow top optima n I'm one cable short on finishing the big three. I was reading on swapping a passat 150a alternator to give me a bit more breathing room but I'm not sure if that's any better than just adding a second deep cycle.
> 
> Advise?:banghead:


I think your math if going to a little off as your tasking the current draw of the amplifier at 100% duty cycle (aka a sine wave). Music does not operate at 100% duty cycle - it's dynamic.

So we'll look at my setup for an example.

I have a T400-4 and a T1000-1bdCP.

Lets say the T400-4 does 100w x 4 (so 400w RMS) and the T1000-1bdCP does 1000w x 1 (so 1400w total RMS power - actual RMS output of the amplifiers are 500w and 1500w respectively but we are going with the "on paper" numbers).

P = I * E
1400w = I * 14.4v
1400/14.4 = I
I = ~97A

That's at 100% duty cycle. Typically music is around ~25% duty cycle so lets say 97A x .25 = ~24A current draw listening to normal everyday music. 

Now that number would be at 100% efficiency which an amplifier is not, no amplifier is.

Say you're amplifier is 80% efficient, it'll take ~ 30A to produce the ~ 24A of current that is require to produce your RMS output at 25% duty cycle.

Say you're amplifier is 60% efficient, it'll take ~40A to produce the ~ 24A of current that is required to produce your RMS output at 25% duty cycle.


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## NFrazier (Jul 22, 2006)

BIGPIMPNfshtx said:


> I'd have to double check on the class Ive had them since 2005. I'm 99% sure the sub amp is a D amp. I saw this video on power http://www.youtube.com/watch?v=5Ckuc2dfVV4&sns=em that's how I got to thinking about power. He says to add up the fuses n that will give you a basic idea of how much power you need.
> 
> If I just upgrade the alternator n use the yellow top by itself, will there be an over charge problem between the HO alt n the yellow top when I'm not BASSin' out?


Well I didn't watch the whole video, but he is most likely just stating the "on paper" current capacity of the amplifiers. If you are going to a competition and running a sine wave at a certain frequency, then yes it's going to be more current needed than everyday listening music.

My old P1200.2 was fused for 120A IIRC but it would in no way pull that listening to music everyday, not even close. It would have consumed all of the available current draw from my factory alternor.


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## BIGPIMPNfshtx (Mar 20, 2008)

I didn't account for the efficiency. So what size alternator/battery setup do u think I would need? I don't do competitions but I do like to be heard for long periods of time.


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## NFrazier (Jul 22, 2006)

BIGPIMPNfshtx said:


> I didn't account for the efficiency. So what size alternator/battery setup do u think I would need? I don't do competitions but I do like to be heard for long periods of time.


What's the amplifiers you have?


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## BIGPIMPNfshtx (Mar 20, 2008)

Two soundstreams. Im gonna have to check on the exact model for the sub amp but its definitely an old model Tarantula (not sure if its mono or 2/4 channel). Its fused for 120A. The second is a 4 channel XTS 720.4. Its fused at 60A. They are both about six years old so id have to look up the detailed specs.


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## mike_VR (Apr 11, 2012)

bump. I'm curious on the comments since I'm just now looking to upgrade my sound.


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## NFrazier (Jul 22, 2006)

BIGPIMPNfshtx said:


> Two soundstreams. Im gonna have to check on the exact model for the sub amp but its definitely an old model Tarantula (not sure if its mono or 2/4 channel). Its fused for 120A. The second is a 4 channel XTS 720.4. Its fused at 60A. They are both about six years old so id have to look up the detailed specs.


If you can get me the model numbers and what you are running on them (impedance, etc.) I can tell you the approximate current draw listening to music.


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## pjd2011 (Jun 17, 2009)

Sorry to but in but now I'm curious after reading this.

Alpine F6 Amplifier (186w rms x 4 channels at 4 ohms)
Alpine M12 Amplifier (1292w rms x 1 Channel at 4ohms)


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## NFrazier (Jul 22, 2006)

pjd2011 said:


> Sorry to but in but now I'm curious after reading this.
> 
> Alpine F6 Amplifier (186w rms x 4 channels at 4 ohms)
> Alpine M12 Amplifier (1292w rms x 1 Channel at 4ohms)


102A @ 14.4 @ 100% duty cycle & 100% efficiency.
117A @ 12.6 @ 100% duty cycle & 100% efficiency.

25.5A @ 14.4 @ 25% duty cycle (the rough estimate of normal music duty cycle) and 100% efficiency.
29.25A @ 12.6 @ 25% duty cycle (the rough estimate of normal music duty cycle) and 100% efficiency.

32A @ 14.4 @ 25% duty cycle (the rough estimate of normal music duty cycle) and 80% efficiency.
36.5A @ 12.6 @ 25% duty cycle (the rough estimate of normal music duty cycle) and 80% efficiency.

80% efficiency is around the efficiency rating of those PDX amps.

Crazy difference between going "by the numbers" and real world applications.


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## BIGPIMPNfshtx (Mar 20, 2008)

NFrazier said:


> If you can get me the model numbers and what you are running on them (impedance, etc.) I can tell you the approximate current draw listening to music.


Sorry this took so long. all my paperwork was in storage. 

sub amp. Soundstream Picasso 1500D - 1100Wx1ch @ 2ohms
multi/ch Soundstream Xstream xta720.4 - 90Wx4ch @ 4ohms


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