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post #1 of 4 (permalink) Old 12-17-2004, 05:30 PM Thread Starter
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OK Question 1

I need extra power, i have a Capacitor, but my setup requires some more energy, for lighting ,dvd player etc.... I heard of somehting called an Isolator which transfers power to an extra battery (i happened to have an extra one) Anyone know refrences i may follow to
make this happen?

Second question, Will tapping signal from internal car speakers to 2 extra tweeters cause damage to internal amplifier? I'm looking to add these for much needed highs.
i found a good mounting point behind the corner leather sides on the back seat.

i am performing another trunk re-arrangement, and i wanna get it perfect. new pictures will follow
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post #2 of 4 (permalink) Old 12-21-2004, 02:51 AM
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I messed around with a two battery setup when I first got a car and into car audio. I got 3 amps running. I had a 4ch Alpine v12 for my surrounds and 2 Memphis 1000D's brigded to power a 15inch CV Stroker at 2 ohm. Happy to say I busted 143.8dB with a sandbag on the gas to keep my alternator running enough juice even with 2 batteries.

Now as an Electrical Engineer I understand what was happening more.

The big problem with two batteries in parallel to maximize the energy demanded needed to power such a big setup is when the charging system is not running ie your car is not running. The two batteries form a closed circuit. Every battery has its own voltage and internal resistance based on the efficiency of the chemical reaction. When connected into a circuit as you would in your car, current will flow and will discharge the higher potential battery (higher voltage) down to the lower potential. Beyond that point current drop because it is now in equilibrium. During operation when your car is running and charging system engaged, the voltage difference is droped over the internal resistance in the higher potential battery, thus providing a single voltage source to the car.

Whats recommended to do is install a battery isolater. Its basically two large, high current diodes (50-100A) that allow current to flow down from your charging system into each battery independently and disallow any current flowing between batteries. It basically allows you to operate two batteries indenpendently while charged with one system. So you hook up your HU, Montiors, and other accesories on battery A and have your amps on battery B with a capacitor for high insantanious current draw when your bass highs to say.

Another option is a high current circuit breaker. It looks like a .5 Farad cap, with a remote turn on. This would be wired in line to the battery B on the (+) and would be activated by either remote turn on from your HU or ignition ON/RUN. While ignition OFF, in either ACC or neutral key positions, battery B is not connected in a circuit with battery A. Thus gainning independence while your car is off.

So having your system connected in the same manor as above in both battery 'isolations', you turn your key to ACC and your HU runs off of battery A and amp on battery B. Start your car or turn to RUN and the batteries are now in parallel. Both setups have the same advantage in that you can always start your car after your amps use up all the juice in battery B.

Hope that will help you and I havn't mislead anything.


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post #3 of 4 (permalink) Old 12-21-2004, 10:46 AM
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I have a 318i, it isn't fast at all so I always achieved my cool points with it in the sound system catagory. The system I first had I wasn't satasfied with so I put in a much larger one (two punch 2's and 1200watt peak fosgate amp) this pulled an imense amount of power form the car, I could see the lights dimming to the music. It concerned me alot so I purchased a 2.5 farad capacitor. It helped some but there was still noticable dimming.

I came out to my car one morning in dismay, to find out that my car had both drivers side windows smashed in and the system stolen. So I set about building a new system and protecting it. This time I knew more about power demands ect, so I put in two batteries optimas one red top and one yellow top (yellow tops are praticularly good for being drained again and again). I hooked the yellow top to the new system (two JL w6's and a 1000watt rms regulated 1000/1 JL amp). It was unimaginably loud, probably in the 140db range (just a guess). I needed to isolate the batteries so that the system could not pull power fom the car like the last system did. I isolated the bateries (hook up the batery one, two ect. very simple), and there was no more dimming. So I had a system running far far far more power and not dimming the lights like my wimpy system had. Isolaters are better than capacitors! If you go to and car audio place they will try to sell you and isolator, the truth is most car audio expert places aren't very good. As it turned out the power pulling that the first system did lights dimming ect had caused major electrical problems with my car, the voltage regulator had gone bad. That caused a series of problems I'm still trying to fix today.

I had and alarm installed, but the system got stolen again. If you learn anything from all my misfortune, learn to take out your deck faceplate everytime you leave your car, and that isolators are better than capacitors.

If you have and questions on how to install your isolator i would be more than willing to give more help. Oh and the tweeters take up such a small amount of power that it won't damage anything if you hook it p to the amplifier. Remeber, don't use the capacitor use the isolator!!!!!!!!
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post #4 of 4 (permalink) Old 01-04-2005, 02:03 PM
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why not get a higher output alternator?

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