battery vs capacitor

[1988_5spd_lxi]

can i use a extra battery in my trunk instead of using a capacitor?
how will i configur it? i think i will use a 4 guaged from my main postive output battey to my trunk, then ground my battery in the truck.

the reason i want to try this is beacuse it will be cheaper. i can get a battery for $40.00

Will it work, with out damaging my car. :super:

[87DXHatch]

You can use a battery in your trunk. However, batterys and capacitors serve different purposes.

Batterys store charges for long periods of time, with a slow discharge rate. Capacitors store charges for short periods of time, with a very high discharge rate.

I believe you will run it in parallel with the other battery.

How much power are you running? At the moment I'm running about ~850 watts total RMS and I have 0 dimming... if you have dimming, upgrade your underhood wires before buying another battery or a cap. The wires are:
Engine block to chassis
Negative battery to chassis
alternator to + battery

Upgrade those wires to at least 4-guage and kiss your dimming goodbye... unless you're running multi-thousand watt amps.

[AccordEpicenter]

I think if youre running that much power or above you need serious alternator upgrades, or youll probably fry it sooner or later. Also, i was running a rewound (put out 140 amp cold, maybe 115 hot) and it powered my stuff with little problems (1250WRMS, thats about 85 amps just for the 1200d etc) and i had very slight dimming at full volume, but i didnt have a cap. Big ground straps help very much.

[87DXHatch]

How much was the re-wind again, AccordEpicenter? I'm looking into doing that soon... I'm going to be running around 1300 rms.

[1988_5spd_lxi]

i have one amp with 600 watt the other 800 watt
= 1400 watt what size cap i will need?

[HostileJava]

I believe if you use two batteries they get wired in parallel but you need a battery isolator on one of them or they will both discharge into each other back and forth. Because of the internal resistance in the batteries, which causes loss of power, they will eventually go dead. I could be wrong about that, I'm really not sure.

[87DXHatch]

That's not true HostileJava, they will not discharge into each other back and forth to the best of my knowledge, the only thing an isolater does is that it kicks in when the car is off so you only drain the trunk-located battery with your system, not your starter battery.

1988_5sp_lxi: you don't need a cap, period.

[Vinny]

isolator allows each battery to be charged by the engine alternator, but does not allow a drain from one battery to the other. think of electricity as water. Electrical current is equal to the flow of water and voltage is equal to the pressure. The alternator pumps current (water) into the batteries (storage tanks). The current then flows through the wires (pipes) to the accessories. It's important to think of batteries as storage tanks. If a fully charged battery is connected directly parallel with a discharged or empty battery, the voltage pressure in the full battery will force its current into the empty battery until the current stored in both batteries reaches a common level. The discharged battery will always rob power from a charged battery. So no matter how many batteries you have on your vehicle, the accessories connected to one will draw power from the other batteries in the circuit unless you have an isolator :rolleyes:
As far as the cap goes, I had to use one with my old system I was running a ppi A600 and an a404. The amount of pull required for the a600 without a cap caused it to short internally. Use a cap if you have a system that may take short periods of hi power requirements

[AccordEpicenter]

My rewound was like $140 or so. Battery isolators arent the greatest for car audio, they drop nearly .7-.8v across them (they are just a big diode) and cost some power due to heat. It comes down to this, if you were at 12.5v you could be down to 11.7v after the battery isolator (kills your amps power) 2 different sizes or types of batteries can discharge eachother if left hooked up all the time. The best part about isolators is that you can completely discharge the battery for the audio but the car battery will not discharge because it is isolated.