Current draw in an amplifier?

November 13, 2010 at 12:22:57
Specs: Windows Vista, 3.199 GHz / 1526 MB
So I have had this dilemma for over 2 years now, it seems not a single soul in this world has a clue of the answer.

I am wanting to run a car audio amp in my house. Seems easy right? Just get a 12 volt power supply with "any old amp rating" and you good to go! Problem is that "any old amp rating" is going to starve your amp, did someone bring marshmallows?

Logic says the fuse rating on the amplifier is the maximum current draw of the amplifier. My amp has a 125A fuse. So with my thinking, I need a 12 volt power supply rated at 125A. This makes since because the amp is rated at 1500wRMS @ 2 ohms stable mono. (12x125=1500)

Let me back up a bit... The amp is a Kicker ZX1500.1. 1500 meaning 1500W (@2ohms stable) .1 for mono.

What about a car battery though..., what is its continuous amp rating while being 99% charged from a battery? Extremely few people know! I recently came across a formula--

Continuous amps = Amp Hour rating / Charge-Discharge Time (hours)

This is supposed to be the continuous current of a battery... but wait... I don't know if (the battery I have) even supplies 125A continuously! (insert dilemma of in line fuses)

I've seen people on Youtube who use battery chargers rated at 5 amps to power high end amplifiers in their home. WTH sense does this make? Charger- "Here you go Mr. amp! Here is (12Vx5A) 60w of power!
Amp- "YAY! wait... where is the other 1440 watts? I'm starved!"

So back to my original question: What is the best way to determine how many continuous amps you need from a power supply to power an amp at home with given parameters?

Am I right on the dot with logic? or am I completely lost in thought...... Don't tell me just use a home theater amp. There is not a single one in this world that will push 1500Wrms+ at 2 ohms with a low pass filter.

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November 13, 2010 at 12:53:16
The amount of power required by an amplifier will vary widely depending on the sound output. And this also varies widely. The amplifier has a high power output rating to prevent clipping on peaks which will typically be many times the average output level. Under typical conditions an amplifier rated at 1500W won't require anywhere near that much average power input. 65W input will provide a lot of sound but will clip on high level peaks.

How much power input will you require? That depends entirely on how loud you play the music.

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November 13, 2010 at 14:13:11
Continuous amps = Amp Hour rating / Charge-Discharge Time (hours)

The Amp Hour rating is the current the battery will provide for one hour unill it is 99% discharged.

Therefore if a battery rated at 100 AHr takes 2 hours to discharge it will be providing a continuous currant of 50 Amps. If it discharges in half an hour then it is providing a continuous current of 200 Amps.

A battery rated at 125 AHr is going to be a big battery, If you can pick it up and carry it yourself its not going to be big enough. Remember also that some of that input power is going to be lost through heat. An amplifier knocking out 1500 W is going to get a bit warm.

Another thing to remember as well is that the input power is DC. The output is AC. The output of an amplifier is usually measured in RMS as we are dealing with a variable wave output . However the peak power is sometimes used which makes the amplifier sound more powerful than it really is. It is important to know which one the 1500 watts is referring to.


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November 13, 2010 at 15:20:30
Your fuse is not what it draws. You'd need to put an amp probe on the setup at full power and then tell. I suspect you already know volts x amps = watts. Your watts output can't be guessed as you don't know another part. It may be guessed if you consider 8 ohm speakers but a guess.

Consider some sort of battery based power supply and then charge it. That is the only way a 5 amp charger could work.

Why did it take me over a year to phone in a problem to ATT?

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November 13, 2010 at 21:51:56
Look again at the fuse. I can guarantee without a doubt that it says 125 volt rating, not 125 amps.

You trying to reverse engineer an amplifier and spending way too much money and effort to do it. I see where you're going and although it is fun to engineer a project like this, you could spend half the money buying a home system.

Besides, when you drive an amp to it's limits by loading it down with a 2 ohm load, yes you can get a high wattage rating but at a price. Your dampening factor drops radically as does your THD (total harmonic distortion). Dampening factor is the specification that says how well the speaker travels to the actual waveform driving it. A low dampening factor will result in the high end sounding harsh and the bass sounding muddy. Harmonic distortion is pretty self explanatory.

Something else you will want to factor in when buying a power supply is how well it can keep up with transient power draw. Most high end car stereo systems will put a huge capacitor at the input of the amplifier to be. Able to keep up with transient voltage draws.

By the time you factor in all the problems with running a high power car stereo system in your house, you really would be better off just buying a home stereo which has been designed for its environment

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November 15, 2010 at 12:49:40
These big amps do have 125 ohm fuses or higher installed. I installed a 4000 W inverter in a work truck and used a lot of the parts from these car installs to do it. Lucky it brings down the price.

Why did it take me over a year to phone in a problem to ATT?

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