what size batteries and alternators?

[Fi-brations 10+ year member]

Im going to be going from running 1300watts for subs and 200 watts for my comps, to running 3000watts for my subs, same for comps, im going to run 1/0 gauge for the power and grounds of the amps, and the battery ground. Im going to get a HO alternator and battery(ies). What amp alternator should i get, ive been told somewhere around 200A-220A. Ive also been told to get two group 31 batteries, but if i can i would much rather get one, then spend 800 on batteries alone. So could i use my stock battery for everything besides my system, and use the group 31 one for my system? or would it be better to use them both for my system and everything else(im not really sure how multiple batteries work sorry) my stock battery is pretty large, the only spec i have on it is that it has 1000 cranking power.

So, basically, what size alternator to run 3kwatts, and how many and what size batteries can i get away with?

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[sacsking916 5,000+ posts]

Why make another thread when the question was already answered? Plus batts aren't 800 you can find batts much cheaper. Hit up ram he has battery's so does bad4health.

 

[Fi-brations 10+ year member]

Why make another thread when the question was already answered? Plus batts aren't 800 you can find batts much cheaper. Hit up ram he has battery's so does bad4health.

I was getting many different answers, and i wanted to keep it fresh and summarized, b/c i personally dont want to read through pages of posts to understand the thread

im also now being told that i dont need a ho alternator, so im kinda confused, and btw my stock alternator is a 120A

 

[Papermaker85 5,000+ posts]

yes you need a alternator..

you don't need batteries..

if your alternator can supply the amp(which is ideal) adding a battery will do nothing..

if you have 3500watts you need a alternator capable of producing that power..

3500/13= 270 amp..

that's with 100% efficiency..

if you can find a 300 amp alt that would be ideal..

 

[Fi-brations 10+ year member]

Ok, this is getting confusing, b/c one guy is saying i need alternator no batteries, and another one is saying batteries no alternator. I dont know.

 

[audioholic 5,000+ posts]

yes you need a alternator..you don't need batteries..

if your alternator can supply the amp(which is ideal) adding a battery will do nothing..

if you have 3500watts you need a alternator capable of producing that power..

3500/13= 270 amp..

that's with 100% efficiency..

if you can find a 300 amp alt that would be ideal..

Batteries create a buffer for when the alternator cannot provide enough current to satisfy the draw.

What you guys need to remember is you must look at power used versus power supplied over time, not as a single snapshot in time where the amp(s) is pulling maximum current. If the amps being used were class A, which does pull full current all the time, papermaker's math above would be spot on. But a/b and d class amps' current draw is transient, it scales with the output required/achieved.

Since the power demand goes up and down, its reasonable to assume there will be periods of time when the alternator can provide enough current, and times when it cant. If there was no battery in the circuit, the times when demand exceeds supply, system voltage would simply drop to a level that would either send the amp into protect mode, or possibly damage it. The batt is a stored power supply that will pick up the slack when the demand exceeds supply. The bigger the batt you have, or the more of them you have, the greater those periods of demand exceeding supply can be, or the greater the difference between demand and supply can be.

Ok, this is getting confusing, b/c one guy is saying i need alternator no batteries, and another one is saying batteries no alternator. I dont know.

Prepare to get more confused, this topic is more complex than people usually make it out to be. Many things factor in to how big an alt you need, how much battery storage, etc. Things like listening habits, such as how often you listen to the stereo versus how often you drive with it off, how loud you tend to listen to it, etc. Even what type of music you listen to can affect it, as some types of music tend to be more bass heavy than others. So as you can imagine, its impossible for us to give you an exact answer as to what you need. At best, in cases of extremes, like where a guy wants to run 5kw off his stock 90amp alt, daily, we can tell the person they need a bigger alt. But when the differences in supply and demand decrease, listener's habits become a bigger factor and ultimately make any math equation we offer as a guesstimate at best.

Papermaker's math above is theoretically correct, and once the 270amp is multiplied by 1.2 to factor in for the average amplifier efficiency of 80% (approx 325amp), it tells you approximately what the maximum current draw of your stereo. You then need to think about the intangible factors I mentioned above and decide if you think you are even in the ballpark of having a big enough alt. If you think you are in the ballpark, you can get a couple big batts, upgrade the big-3, and drive around with jumper cables in your trunk in case you need them. If you aren't in the ballpark, you need a new alt.

You can run a new batt in the trunk and keep your stock batt under the hood. But running two batts in parallel that dont have the same or close to the same internal resistance can cause a parasitic drain problem. I usually recommend replacing all batts in the circuit at the same time, or using an isolator to isolate the front and rear batt circuits.

 

[Ninesvnsicks 10+ year member]

If you have the money for a ho alt then it sounds like a 300amp would be all you need. You can look at the fuses your amps use that will tell you how many amps you are drawing just with the amps alone.

 

[audioholic 5,000+ posts]

Again, an amplifier's current draw is transient. Adding fuse ratings together will only tell you what the amp might almost pull, once in a while, for a brief period of time. Unless he enjoys listening to sine waves at full volume continuously.

Even if he does end up needing a new alt (and I suspect he does, but I dont know what size alt his bmw has stock), he wont need a 300amp unit.

 

[Papermaker85 5,000+ posts]

Batteries create a buffer for when the alternator cannot provide enough current to satisfy the draw.
What you guys need to remember is you must look at power used versus power supplied over time, not as a single snapshot in time where the amp(s) is pulling maximum current. If the amps being used were class A, which does pull full current all the time, papermaker's math above would be spot on. But a/b and d class amps' current draw is transient, it scales with the output required/achieved.

Since the power demand goes up and down, its reasonable to assume there will be periods of time when the alternator can provide enough current, and times when it cant. If there was no battery in the circuit, the times when demand exceeds supply, system voltage would simply drop to a level that would either send the amp into protect mode, or possibly damage it. The batt is a stored power supply that will pick up the slack when the demand exceeds supply. The bigger the batt you have, or the more of them you have, the greater those periods of demand exceeding supply can be, or the greater the difference between demand and supply can be.

Prepare to get more confused, this topic is more complex than people usually make it out to be. Many things factor in to how big an alt you need, how much battery storage, etc. Things like listening habits, such as how often you listen to the stereo versus how often you drive with it off, how loud you tend to listen to it, etc. Even what type of music you listen to can affect it, as some types of music tend to be more bass heavy than others. So as you can imagine, its impossible for us to give you an exact answer as to what you need. At best, in cases of extremes, like where a guy wants to run 5kw off his stock 90amp alt, daily, we can tell the person they need a bigger alt. But when the differences in supply and demand decrease, listener's habits become a bigger factor and ultimately make any math equation we offer as a guesstimate at best.

Papermaker's math above is theoretically correct, and once the 270amp is multiplied by 1.2 to factor in for the average amplifier efficiency of 80% (approx 325amp), it tells you approximately what the maximum current draw of your stereo. You then need to think about the intangible factors I mentioned above and decide if you think you are even in the ballpark of having a big enough alt. If you think you are in the ballpark, you can get a couple big batts, upgrade the big-3, and drive around with jumper cables in your trunk in case you need them. If you aren't in the ballpark, you need a new alt.

You can run a new batt in the trunk and keep your stock batt under the hood. But running two batts in parallel that dont have the same or close to the same internal resistance can cause a parasitic drain problem. I usually recommend replacing all batts in the circuit at the same time, or using an isolator to isolate the front and rear batt circuits.

it's really quite simple if the alternator is capable of producing the maximum amperage required doesn't need to upgrade the battery, the battery will simply be used for starting..

adding a battery often helps stabilize your voltage when the alternators output is exceeded but if you constantly exceed it's output tour going to burn it and evently kill the batteries..

I don't know of one battery that can discharge fast enough to stabilize current ripple..

if you want to build a very dynamic system that really helps on current draw there is one solution but it's going to work as long as it's somewhat dynamic..

I've never said this but I will here because I know it works fine..

you need enough capacitance to supply you maximum current draw for 30 seconds with out completely discharging..

it does the exact opposite as what it's designed to do making the alternator couple with the caps..

seeing as the caps will never fully discharge so you alternator never has to supply the amp, just jeep the caps for completely discharging..

this is exactly the same way the RF 15k amp works..

if your willing to do so you won't have to upgrade your amp but your going to pay for the caps..

you need about a 5 to 1 ratio of farad to 1kw of output.

so if your total is 4kw you would need 20 farad..

and nit those ******** 50 to one caps..

 

[Papermaker85 5,000+ posts]

BatCap 4000

2 of these would hold you at around 13.2 to 13.5..

 

[audioholic 5,000+ posts]

it's really quite simple if the alternator is capable of producing the maximum amperage required doesn't need to upgrade the battery, the battery will simply be used for starting..
adding a battery often helps stabilize your voltage when the alternators output is exceeded but if you constantly exceed it's output tour going to burn it and evently kill the batteries..

I don't know of one battery that can discharge fast enough to stabilize current ripple..

if you want to build a very dynamic system that really helps on current draw there is one solution but it's going to work as long as it's somewhat dynamic..

I've never said this but I will here because I know it works fine..

you need enough capacitance to supply you maximum current draw for 30 seconds with out completely discharging..

it does the exact opposite as what it's designed to do making the alternator couple with the caps..

seeing as the caps will never fully discharge so you alternator never has to supply the amp, just jeep the caps for completely discharging..

this is exactly the same way the RF 15k amp works..

if your willing to do so you won't have to upgrade your amp but your going to pay for the caps..

you need about a 5 to 1 ratio of farad to 1kw of output.

so if your total is 4kw you would need 20 farad..

and nit those ******** 50 to one caps..

Yes, in a perfect world we can all afford to just buy an alt capable of always covering the current demand.

If you constantly exceed your alt's potential, then yes just adding a batt is not the solution. I think I covered that above.

I didnt say a batt would remove current ripple. Current ripple, and caps, are a whole other discussion.

Your idea of 5 farad per 1kw would be considerably more expensive than just buying a HO alt.

 

[Papermaker85 5,000+ posts]

my point exactly...

 

[Fi-brations 10+ year member]

Thank you all very much, its really nice to get such an informative answer. Im not exactly sure what i can tell you, but I listen to bass heavy music almost all the time and I listen to music whenever im in the car. I drive the 15-20min to school and back on weekdays, and i drive around a lot on weekends. In my current setup, listening to my bass all the way up is no problem for my ears, the only thing it starts to do and higher volumes is distort my speakers, i have no idea how loud my bass would be if i more than doubled the amount of watts going to each sub, so i doubt i would listen to it at the highest level of bass all the time. So is there anyway i can find out what amp alternator combined with what batteries would supply me with enough power to handle everything? what i was thinking was get two kinetik hc 1800s and use those just for my amps, then use or replace my starter battery which is in my trunk with an identical stock battery which is very large. I would do big 3 with 1/0 gauge and use that also for the power and ground of the amps. I would think that would all work, but if my alt is a 120A, would it charge them fast enough? Your giving me a lot of information and its helping to get the correct answer and a real answer, but its hard for me to apply it to my own situation, and ive heard so many things about caps being bad and good. It seems like a very controversial topic.

Edit: and also if i do need an HO alternator, i still have not been able to find someone who makes them for bmw at that level of amps, and i have not heard back from excessive amperage

 

[Ninesvnsicks 10+ year member]

Hey guys I found an xs power D5100 for $113 it says it can handle 3100 watts as a 2nd battery do you think that it's a good deal and is it a normal deep cycle?

 

[Fi-brations 10+ year member]

Hey the guy at excessive amperage told me that he can build me a 200A alternator, direct bolt on, for $395 free shipping. Is that a good price, and would a 200A and two kinetik hc 1800s, and a lot of 1/0 gauge for everything be good? my previous post tells my listening style and such.