250amp alternator,why would an extra battery be needed?

[Germ305 10+ year member]

So I was just having a discussion with Imtjnotu through the IM thing and he is telling me for that amount of wattage I am planning for, i need an extra battery...some one explain this to me properly please because as long as i have been around cars and fixed them, the battery is just i guess you can say a reserve in the event your system draws more than what the alt can handle?...this is quoted from DC power just as a reference to prove my point.

"The battery is required to “fill in” what the alternator can’t – albeit at a much lower voltage. A fresh battery will do this for a while, but it requires charge from the alternator to keep it fresh"

For instance...Tj states that a car will not keep running if you pull the battery,Batteries to MY knowledge are just used to start the car...as soon as the car is running the alternator takes over and powers the car. Thus the car should be able to run till it runs out of gas,as long as you do not exceed the amperage of the alternator.

After using some of these amperage calcs i found it states for a 250amp alt that will produce the full 250 @ 1,200RPM the system alone (2,400rms) would draw 163@14.7v...and 194@12.5 and i'm guessing that would be at full tilt or just a heavy bass note as music is dynamic. and then given the rest of the accessories in the vehicle (AC,lights,fuel pump,coil,Power windows,etc) it would draw roughly 100a if you were to do all this ALL at once. Obviously coils,fuel injectors,fuel pump and such are always going to constantly draw power to keep the vehicle running so i would say 60-70a constant give or take a few.

My car runs i believe at 13.8-14.5 IIRC. If i am not using the full 250a and i have 0/1 gauge all around including the "big 3"...why would i need a battery if i do not plan on playing music with my car off?

If a battery is needed no problem...I'm just trying to find the logic in this that is all. Any replies would be appreciated.

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[Imtjnotu 5,000+ posts]

Bump

 

[Bettr n' Revrse 5,000+ posts]

Like I said a small one in the back wouldnt hurt or a big D3400/3100 in the front

 

[Bettr n' Revrse 5,000+ posts]

Like this one... http://www.caraudio.com/forums/electrical-wiring-classifieds/526218-kinetik-hc600.html

 

[Heeltoeclutch 10+ year member]

I know for a fact that a car will keep running if you pull the battery - some older subarus have a light on the instrument cluster that lights up to tell you you've gone too crazy and the battery has become disconnected, i.e. if you turn the car off it won't start again until you hook it back up. Happened to my friend while we were having some parking lot fun in the snow - his car kept running like nothing had happened and we drove back to school after playing around more before hooking it back up.

 

[VWBobby 10+ year member]

The battery is more of a 'reserve' if you want to call it that. It gives your system more total capacity. Allows you to 'surge' more power than your alternator could ever hope to provide.

What a lot of people on this forum fail to realize is, It doesn't take a lot of amperage to charge a battery, when demand is not constant (test tones). The systems with the 10 batteries and 10,000 watts don't all have 1000's of amps of alternators to charge all those batteries. The biggest install I've seen was 4 alternators, around 1000A. Like you hinted at above, "music is dynamic". This gives the alternator a chance to charge the batteries between the beat. If you ran a test tone for a long time however, you would drain the batteries much quicker. I've ran many of systems on smaller 75A alternators (~1500 RMS) and 1 extra battery with over 13V. Anything less than the battery(s) resting voltage is no longer charging. Anything over resting voltage is a positive current flow (charging).

 

[ahole-ic]

imtjnotu is trying to help you but unfortunately you are actually correct and he is not. A car will run just fine without a battery. Literally everything you said was correct. The only way a battery may help you is, that battery in the rear will be connected to the amplifier with just a foot or two of wire. There will be almost no series resistance between it and the amp. So, the series resistance in the power wire between the alternator and the amplifier could not cause you a big problem because that batt in the back is there to keep the voltage up above 12v. That's why I have batts in the back.

 

[Falcons 5,000+ posts]

imtjnotu is trying to help you but unfortunately you are actually correct and he is not. A car will run just fine without a battery. Literally everything you said was correct. The only way a battery may help you is, that battery in the rear will be connected to the amplifier with just a foot or two of wire. There will be almost no series resistance between it and the amp. So, the series resistance in the power wire between the alternator and the amplifier could not cause you a big problem because that batt in the back is there to keep the voltage up above 12v. That's why I have batts in the back.

Ecrack where ya been broskie????

 

[i2ain2thunder 10+ year member]

I dare you to go disconnect all batteries run your car and try to turn your volume up. Science aside every system is different electrically. Better to connect stuff and see if it helps if so keep it if not return it. In my experience even with a high output alternator a second big battery in the rear has always helped output for me.

 

[kramer_212 10+ year member]

well, from what i was told you "should" have an hot pulse amp in your battery. 1 amp per 1rms watt, to properly power your system........not counting the starter battery should have a second no matter what.........and ive seen this many times you will melt the battery cells together especially if its a wet cell.

 

[Germ305 10+ year member]

I dare you to go disconnect all batteries run your car and try to turn your volume up. Science aside every system is different electrically. Better to connect stuff and see if it helps if so keep it if not return it. In my experience even with a high output alternator a second big battery in the rear has always helped output for me.

"as soon as the car is running the alternator takes over and powers the car. Thus the car should be able to run till it runs out of gas,as long as you do not exceed the amperage of the alternator."

 

[akheathen Premium Member]

^^^huh? explain this "hot pulse amp"

anywhoo, to answer simply, a bigger and/or more batteries will help to keep the system voltage constant and smooth. now, for more detail, first, when you calculate your current draw vs wattage, you need to take into consideration the amplifiers efficiency, which will vary greatly at different volumes, impeedances, and supply voltages, and different amps have different efficiencies. rule of thumb- 1amp will get you 10watts, though that is just a rule of thumb, and only vaguely close. next, and alternator is generally a maintenance device, intended for anywhere between 20-50% duty cycle depending on the vehicle manufacturer. the age old teachings for mechanics, is that the alternator runs the car electrical, and the battery starts it, and the alternator is only rated for peak power draw, including all factory options. the quick sop to see if the alternator is working is to disconnect the battery and see if the car dies. now, alternators are ac generators that inherently put out an ac ripple on top of the sustained dc voltage. this is not the greatest thing for the electronics running off of it, aside from simple devices like filament lights and motors. alternators also have a slow response time, relatively speaking, for it to adjust to voltage drops and peaks, this is usually what you see when the lights dim with a bass thump, where you are still only drawing less current than what it can really support, also why capacitors seem to work, though they really don't do what most think (give/boost power). as for the maximum rating of an alternator- there will be voltage sag before it reaches max current, so even though you have 250a on tap, you might only see 200a above battery voltage, but that depends on the manufacturer of the alt. now, for battery useage and performance- this is how it dampens and smooths: the battery stores power, and can supply large amounts of current, however, there is also "sag" there, too, so there is only x amount of current you can pull from a battery before you will see an undesireable drop in voltage. anything that it is holding above resting voltage is aslo significantly lower amount that what it can supply below that resting voltage, since it does not really want to store it, as is evident when you shut the engine off and drop about 2v. if you want the most power, you want to maintain the higher voltages. you do not get the same power at all voltages, rather, loose power as the voltage drops. that is exactly why you see systems built to run 16, or 18v, and pull 10k from a 3000d, i.e. and, just in case you are starting to think cacitors might be somewhat of an option to store the same voltage, don't. 1farad is a fraction of a percent of what you can pull form a battery, and that is depleted in a fraction of a second on most systems that you would think need it....

 

[Germ305 10+ year member]

well, from what i was told you "should" have an hot pulse amp in your battery. 1 amp per 1rms watt, to properly power your system........not counting the starter battery should have a second no matter what.........and ive seen this many times you will melt the battery cells together especially if its a wet cell.

What is a hot pulse amp in a battery if you do not mind explaining?

 

[akheathen Premium Member]

"as soon as the car is running the alternator takes over and powers the car. Thus the car should be able to run till it runs out of gas,as long as you do not exceed the amperage of the alternator."

the alternator is always powering the car, save for "on-demand" alternator systems, which will actually shut the alternator off at times and run battery power, but there is not too many of those running around. you can pull as much juice as you want, and it will not die untill you drag it down to a certain voltage, usually about 10v, or even a bit lower on some older engines, it is either the minimum voltage rating of the ecu/injectors, or the point that the spark becomes to weak to not blow out, or ignite the mix.

 

[Germ305 10+ year member]

the alternator is always powering the car, save for "on-demand" alternator systems, which will actually shut the alternator off at times and run battery power, but there is not too many of those running around. you can pull as much juice as you want, and it will not die untill you drag it down to a certain voltage, usually about 10v, or even a bit lower on some older engines, it is either the minimum voltage rating of the ecu/injectors, or the point that the spark becomes to weak to not blow out, or ignite the mix.

I have seen the ones that shut off. pretty cool chit.

Also chances are i will not play this system full tilt when driving (maybe a little loud but def not full tilt)...Only time i ever plan to do that is when i demo it...and even then it will last maybe a minute or 2.