Alternator & Batteries Advice

[Migz]

Hey,

Today i was listening to my music as usual and for the first time ever my battery died, had to bump start my car and leave it running for a bit. I'm running a bog standard battery and alternator so I've decided its time to up my power a bit as my system is starting to become a strain on standard power.

I've got a 4 channel 100wRMS x 4 Vibe Blackbox Amplifier and a 1 Channel 400wRMS Orion Cobalt Monoblock. I'm pretty sure both have 2x 30A Fuses.

First of all can anybody tell me what the formula is to work out how long i can play music at full volume for before my battery is dead? I'm pretty sure my battery is 50ah i think. How can i use that along with the total of 120A from my Amps to work out how long until my battery is dead.

I also need some advice on what alternator to get, my car is a Volkswagen Golf Mk3 if that helps at all.

And what battery to get. I have absolutely no clue what numbers i should be looking at on batteries, there's CCA, ah and others. But i don't know which one means how long the battery will last playing music before it dies.

I'm sorry if anything i say doesn't make sense, there's so much to learn about batteries that I'm getting quite confused.

Edited March 3, 2011 by Migz

[Neo_frog]

So...you're playing your stuff for a very long time with the car off, and it dies. Why not just keep an eye on your voltage then? You'll have no problems.

[badazz619]

hey everyone my first time posting....i need some advice about alternators..i have a 95 integra stock alternator running 1 500/1 JL amp, 12 inch RE Audio Se-x dual 2 ohm subwoofer, 500k farad cap.....1 zapco ag360 for mids... the problem is when im bumpin my lights dim then power to the system cuts then turns back on!!!! i need to what kinda alternator if i upgrade any help pls

[AMI CUSTOMS]

To the OP, depends on idle output of your alternator. You have to know exactly how much demand you have in amps, and then how much output your alt has in amps, whatever that difference is you have to maintain by battery. If the difference is over 100, then you will drop voltage generally to resting voltage which is ~12.8 on an AGM battery, on a standard battery general ~12.5, IF you are want to play your stuff for hours, then you need to look at RC of the batteries you select, the ah rating is done at a low and slow current draw so means basically nothing in car audio. And the formula to figure this out is a exponential inverted parabolic function, kind of pita to calculate and requires some calculus knowledge to calculate correctly.

[sprkn_ranger]

And a good place to get an alt is mechman, he has a section on the forums here, but it's best to email directly or call as they are real busy and don't always get to the forums.

[831Arevalo]

hey everyone my first time posting....i need some advice about alternators..i have a 95 integra stock alternator running 1 500/1 JL amp, 12 inch RE Audio Se-x dual 2 ohm subwoofer, 500k farad cap.....1 zapco ag360 for mids... the problem is when im bumpin my lights dim then power to the system cuts then turns back on!!!! i need to what kinda alternator if i upgrade any help pls

just add a battery

[AMI CUSTOMS]

hey everyone my first time posting....i need some advice about alternators..i have a 95 integra stock alternator running 1 500/1 JL amp, 12 inch RE Audio Se-x dual 2 ohm subwoofer, 500k farad cap.....1 zapco ag360 for mids... the problem is when im bumpin my lights dim then power to the system cuts then turns back on!!!! i need to what kinda alternator if i upgrade any help pls

just add a battery

Or get rid of the cap, not doing a damn thing.

[badazz619]

hey everyone my first time posting....i need some advice about alternators..i have a 95 integra stock alternator running 1 500/1 JL amp, 12 inch RE Audio Se-x dual 2 ohm subwoofer, 500k farad cap.....1 zapco ag360 for mids... the problem is when im bumpin my lights dim then power to the system cuts then turns back on!!!! i need to what kinda alternator if i upgrade any help pls

just add a battery

Or get rid of the cap, not doing a damn thing.

For the extra battery is an isolator needed? And should I remove the cap or get another one with higher capacity? Thanks

[Rebel4055]

Nice hijack but no, remove that cap, do not get a bigger one or get more of them, remove it and chuck it into the trash.

[Migz]

So...you're playing your stuff for a very long time with the car off, and it dies. Why not just keep an eye on your voltage then? You'll have no problems.

I installed some special terminals on my battery which tell me the volts in my battery for just this reason, but A.) I didn't realise my battery would run low that quickly so i want to help make it last a bit longer. And B.) Im not too sure how im meant to know when its low, because when my bass hits my voltage drops, but then when the bass goes my voltage comes back up. How can i tell if the voltage is low because it seems to just go back up to normal when i'm not playing anything :/

To the OP, depends on idle output of your alternator. You have to know exactly how much demand you have in amps, and then how much output your alt has in amps, whatever that difference is you have to maintain by battery. If the difference is over 100, then you will drop voltage generally to resting voltage which is ~12.8 on an AGM battery, on a standard battery general ~12.5, IF you are want to play your stuff for hours, then you need to look at RC of the batteries you select, the ah rating is done at a low and slow current draw so means basically nothing in car audio. And the formula to figure this out is a exponential inverted parabolic function, kind of pita to calculate and requires some calculus knowledge to calculate correctly.

Not sure what the output is at idle, but it says 70 on it, although thats most likely when it's properly going. I'll see if i can find out what it is at idle, its a bog standard VW alternator though. And how would i find out how much demand i have in amps? I know i have a total of 120 Amps worth of fuses on my amplifiers so it cant be more then that. But how do i know exactly what amount is being used?

Roughly what kind of RC rating will play for how long?

Thanks for the quick replies!