924Board.org

[owenexile]

Hi . Well Im in my Planning phase of Building a box for 2 subs whre my backseat is . Well Basicly i got a new Battery standing around , So i want to use that Battery as an External Electrical Source. I want the Battery To run my Amp And Car Audio on it and charge while the Car is idling/Driving from the Alternator , and when i turn of the car off i want the Battery to Cut the power of , So my Car Audio will only run of the Back Battery Whiles not taking any Power from the Front Battery Which will be my Main Battery For cranking the Engine. I was thinking connecting it up on the Ignition but I figured the Wires will be to thin , I will be Running 12mm Wires From Battery to Battery.

Summory : When i crank the Car , i want Both Batteries to Work Together , And when i turn the Car off , i dont want the Batteries Working together anymore , So say i forget my Radio On , It will only drain the Back Batery's Power , Whilst i can still use my Main Battery 2 start the car and let the back Battery Charge again.
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924 1982 N/A
For some reason theres always a earth problem somewhere with this car...

[Smoothie]

Should be looking for a battery isolator - http://www.bcae1.com/battiso.htm
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[ZODIAC]

why the extra battery? two subs and an amp wouldnt require that elaborate of a setup. and if the concern is the constant power to the radio you just need to wire it to a switched power source, like the ignition wire that you mentioned. you also need to consider wether or not te stock alternator can handle charging the extra battery.
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"Kraut cars, they know how to build 'em".
1977 924 N/A - Red with waterdamage interior
yes...waterdamage is now a color...

[owenexile]

[Rasta Monsta]

[DOCO]

now i dont car woo yer r dats funni rite dar!!!(sory to steal yer wordage dan)
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Doco "where am i going and why am i in this handbasket"author unknown
79 924 N/A "Webster"
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"WEBB STR"

[avaconirl]

What i do is put a relay in the charging line between the two batteries it will have to be one that can take the load of the sub. Wire it in such a way that when you switch on the ignition it switches on the relay, that way when you start the engine only then will the current travel between the batts. The other thing is to wire the radio so it works with out the ignition on.
Hope this helps.

[owenexile]

[9XX Girl!]

[datatrain]

A 3000 watt amp in a car and your sitting within 3 feet of the output.

If you looking to do irreparable ear damage your on the right track. I know your going to enjoy spending time with an ear specialist in the future so you can possibly hear something with a hearing aid. when you get a bit older .

Why do you suppose workers compensation mandates ear protection in loud environments ? Answer... so workers don't become deaf.
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'78 924 NA with Collector plate
33 year old car, with me for 21 yrs
Mint '92 318i BMW
Near mint '98 Buick LeSabre
VE7HFR

[RC]

As with mechanical principles, laws of physics and even what`s good taste, the typical ricer kid has absolutely no idea WTF he is talking about when it comes to audio. And thats before the gross exaggeration of BS specifications by even so called "reputable" brands, but particularly by Chinese imports. Bigger is better, 3KW is thrice as loud as 1KW, more subs is cooler, Doof Doof Doof, WTF did U say, eh?

Even if a 1KW amp is rated accurately using PMPO or PMP, or POP(which is BS & impossible to quantify) the RMS value is around a quarter of that at best. In practice it is a small fraction of the claimed output and then only for milliseconds at the absolute peak of the waveform and measured between negative & positive peaks. Basic maths will illustrate that the maximum possible peak output from a direct 14V supply into 4 ohms is less than 50W. The similar PMP output of most reasonable head units.

To obtain more power than this the voltage needs to be increased by a DC - DC inverter that "real amps" have. A top line unit may reach 90% efficiency at a low duty cycle, such as a varying waveform like most music. Try feeding a continuous sine wave into any amp while measuring output (on a dummy load) and the time the amp survives.

Our ears perceive sound on a logarithmic scale, same as on what the dB unit of COMPARATIVE measurement is based. Dismissing BS power ratings, a 3W amp, feeding the same speaker, will just sound a little louder than a 1W amp. Theoretically a four fold increase in genuine output power is needed for the sound to appear twice as loud. That`s for perfect hearing, those with diminished hearing from exposure to high SPLs will need substantially more.

On the dB scale, every increase of 3dB is a doubling of power, while an increase of 10 (ie. 80 to 90) relates to 10 times the power. So with the same power, a speaker of 90dB/Wm (measured 1W @ 1 meter) will sound twice as loud as a 87dB/Wm.

Here`s some basic reading, google will provide all you don`t necessarily want.
http://en.wikipedia.org/wiki/Audio_power

Rasta has a very valid point. My suggestion if you really want to damage your ears with a SPL of 120dB+ is to simply use headphones. That way others hearing is not affected nor the general community`environment. It will save money, weight, wiring hassles, and fines from the police. No need for a battery relay either.

Now don`t misunderstand me. I like loud music, I have a sub, although used very little due to weight, 8" woofers and a 500W RMS amp.

I also have damaged hearing and speak from experience. Too late now to realize that what the oldies said about loud music was actually true. Life is a learning experience.

[D Hook]

[owenexile]

[mikebola]

the 100w amp I run for my front channels ran pretty hot because I placed it near the lower heating ducts in my Lancer, but I'm only running 40 wpc mids with it (at the right ohm rating). What I did was wired a PC fan in there to keep it cool.
Do you have the correctly rated speaker for your amp? I mean, that's usually why it overheats. if you're using a 2 ohm speaker on a 4 ohm amp, it'll be drawing too much current and run hotter. I was just recently running my 3 ohm RTR speakers across an 8 ohm amp (my lovely pioneer SA8500 series one) and it started smoking after a few hours of record playing
My 200 watt Audiobahn amp gets warm to the touch, but you can still TOUCH it when it's playing the 200 watt 8" kicker sub I'm running. The sub's rated at 4 ohm, so I set the amp to run a single speaker at 4 ohms. if I used a 2 ohm speaker, it would get hot enough to scramble eggs on it. or possibly catch fire.
Also..... running two subs in your tiny little cabin won't make your system sound any better. in fact, it'll likely sound horrible. you need to balance out your audio levels to make anything sound even vaguely appealing. I have a 450 watt sub in my media room coupled with a pair of Monitor Audio speakers, and I have to set it extremely low because the speakers sound so clean and rich at lower volumes that the loud, punchy bass takes away from the smooth treble. it's doubly true in a car, where you can't even effectively direct your mid and high speakers towards your head...
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proud owner of a 1979 924 Sebring Edition with a 931 trans that looks horrible but somehow runs...

[924aussie]

Speakers arent the only thing that causes deafness, I need hearing aids after working in a Computer Server room environment for many, many years. Industrial deafness....

Back to your problem, look at 4WD stores and Jaycar for duel battery setups.

Maybe you just want to put them underneath and sound like a V8

Alan
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green 924 .. 1980 rego 924PSH
1998 Mopar Neon ... sick
2003 Challenger / Montery 4WD
1995 Hyundai Scoupe ... sold
1998 Nissan Silvia ... sons back from OS he has taken it
BIG BLOODY MOTORHOME 300zx Sold
1980 Fire truck Sold