nokio

I am slightly confused....

using my physics skills, i use the equation Power = Current x voltage

therefore current = power / voltage

now with the new sound system i am going to install, the wattage (power) will be about 2500, and the car battery voltage is 12(?).

Thus we get current = 2500watts / 12 volts = 208.33 AMPS!!!!

how can the stock type s alternator keep up with this demand?

CLUofI

power draw is not always 2500 watts, that is the max. Most of the time it will be WAY below that. But you will need another batter for the system.

Edit: Oh, and what amps were you going to get. Dont forget about the other things like fans, lights, and what not.

nokio

thanks, but just a battery?

can this battery be wired to run in series and aid my stock batt and alternator?

also, whats the deal with capacitors? are they needed with a second battery?

thanks in advance

nokio

i just read your edit

the amps are crossfire bmf 1000d 's -

1000 watts rms and 1400 peak so i figured that 1200-1250 would be a reasonable high point and that makes 2400-2500 in my calculations

but then again, i dont know much about amps

mike8_5_8to6_1_9

pick up a remote power generator for 20 from napa...it hooks up to the battery...this is only if you have aftermarket pulleys and youre actually worried(which you really shouldnt be)...max potential output is 1 thing...actual output is another

nokio

and mike,

what does that mean if i dont have pullies?

nokio

one more thing, with my sh*tty 800 watt dual 12" system now, the "D5" gear lights and road lamps dim ... what about with even more wattage?

CLUofI

if you have AEM pullies then it would definatly kill your alternator.

nokio

bump:P

CLUofI

what else were you wondering

nokio

what is the deal with capacitors? do i need them with an extra battery?

also what type of battery should i get

CLUofI

a capacitor is just a small battery. Amps have power spikes when the bass hits hard. The cap or battery keeps the huge power spikes from going though the electrical system which causes the lights to dim.

Most people use optima batterys i believe.

nokio

just to be absolutely clear (once i get stuff plexiglassed off and wired, i dont want to have to rewire)

i should only get a yellow topped optima and caps would be needless?

CLUofI

or you could get 2 caps, but that will run you as much as a battery would.

Edit: do some reading too, check out some car audio magazines. A lot of times they will have walk throughs and what not on this sort of thing.

4pumpedCL

Caps arent really batteries.

A cap is a Band-Aid for the electrical system. Your best bet is to either get your alternator rewound to put out more or just invest in a second battery. Caps should be your last choice. Also upgrade the wire from the alternator to the battery that can usually help alot. Last thing is to upgrade your batteries ground connection. Simply just add one or two 4 Gauge grounds to the battery and connect them to the body somewhere near by.

EricL

Someone forgot that the power on the power amp is the power that is output to the speakers. Unless someone is factoring the efficiency of the amplifier, they are in for a big surprise if they like to play their music at high volume.

There are a number of different topologies used in power amps and the efficiencies listed only account for the efficiency of the amplifier itself. There is also a loss of power in the switching power supply common to 99% of the BIG amplifiers.

Amp efficiencies:

Class A (rare in cars): 20-25%
Class AB (common): 50-60%
Class D (PWM): 80-95%


Switching power supply efficiencies:

80-95% depending on design and cost.


Most of the amps will generally "presume" a voltage of 14+ volts coming from the battery and alternator for their rating.

When you calculate the MAX power required, the following formula can be used to get a "ballpark" MAX requirement:

Following example uses a 1000-watt amp with 80% efficiency (Class D) and assumes it uses a switching power supply with an efficiency of 90%:


1000 * 1/0.8 * 1/0.9 = 1000 * 1.25 * 1.11 = 1388 watts required for 1000 watts to speaker.

So, that 1000-watt amplifier would actually require 1388 watts of input power (using the efficiencies shown).

Using 13volts, the MAX current would be 1388/13 = 106.8 amps @ 13 volts.

(AS others have pointed out, this is the MAX continuous power that is required and could be simulated by driving the amp with a continuous sine wave input.)

Regarding the Caps: They are just there to even out the power "surges" and generally help with transients -- they are NOT a panacea...

nokio

thanks ericl

but sorry to say i beat you to it

the amps are rated at 1400, so the actual output is somewhere around 1000

EricL

The discussion above is a "general" guideline on "assumed" efficiencies (depending on amplifier class) -- that being the main thrust of the "blather". (I would hope that someone who picked-up an AB class amplifier would not use the same “efficiency”…)

BTW -- some published efficiencies (as shown below) can be "total energy conversion" efficiency (amp and switcher included) OR just the efficiency of the "class D" amp.


I grabbed the specs of your amps and here they are:

250x1 @ 4 ohms
500Wx1 @ 2 ohms
1000x1 @ 1 ohm
THD: 1% @ 1 ohm
Input Sens: 0.24 to 4Volt RMS
S/N: 90dB
Damping Factor: >100
Typical Efficiency: 86%
Dimensions: 9.6" x 2" x 13"
RCA Preamp outputs
Remote Bass Control
Var Lowpass Xover 50Hz-250Hz
Var Subsonic Filter 20Hz-50Hz
Monoblock-1 channel design


Are you really going to be driving into 1 ohm? That would make a huge difference in your power needs…

The amplifier shows that is has current to spare and would have the "best" damping at 4 and/or 2 ohms.

nokio

ok now i am lost

wouldnt 1 ohm resistance get the most current to power the amp from the 14.4 volts?

why would i do otherwise?

SiGGy

NO!

Runnin the batteries in series would give you a 24volt system. You want to UP the amps, not volts. Running the batterys in parallel would be what you want.


At 24volts you'd deifnetly kill all sorts of stuff...

EricL

In the case of the amp you chose -- YES!

If you manage to get the batteries (first priority) along with wires as thick as your thumb, you can surely get the "most" power from 1-ohm. (If that is your only concern, then go for it.) However, don't be surprised to find that your are getting IM distortion and other problems if the "supply" voltage (battery(ies) and cables) are not up to supplying the 200+ amps (you mentioned that the lights were dimming in the car with your current setup [yes/no]?)

However, "most" (and there are exceptions) speakers are 2-ohm and 4-ohm. If you are planning on paralleling 2 x 2-ohm speakers, the "effective load" will be 1-ohm and you will send 500 watts to each speaker (a pair of speakers per side/channel).

So, if your only interest is in MAX POWER, sure - go for it. (Although, you would surely want to check the sensitivity of the speakers and don't be surprised to find that some 1-ohm speakers with 1000-watts of input will never come close to putting out the same sound volume as some other speakers with half the input power. If I'm not telling you anything new, excuse me...)

Heck, we used to run 500-watts per side in some well-known recording studios using two, 8-ohm, 15-inch JBL woofers and the bass would make your bones rattle.

(FYI, the Bose (Blows) speakers sometimes use 1-ohm and .5-ohm voice coils to get a lot of sound from a simple 14-volt full-bridge amp (no switching supply)).

AtlCl

When people get pulleys, how do you make sure it doesn't drain your battery and kill your alternator eventually? Just sitting in my car now when it is on and not moving with my small system on causes the lights to dim. Can't see how it would hold up with pulleys.