Current consumption with music

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luckydevil

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Posted: May 25, 2006 at 2:47 PM / IP Logged

I'm doing an install in a 2006 Jetta right now. I'm pretty sure the alternator on this car is rated at 110amps. My friend who I am doing the install for will probably very rarely turn it up, and the vast majority of the time the system will be at mid volume (daily driver). I will also be upgrading all the ground and alternator cables.

Zed Audio lists specs on their amps with musical current consumption and sine wave current consumption.

(at the bottom) http://www.zedaudio.com/Products/Draconia-Spec.htm

Due to the fact I know that the volume won't be cranked all the time and he won't be playing sine waves, would it be reasonable to install a bigger amp than usual?

stevdart

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Posted: May 25, 2006 at 3:48 PM / IP Logged

The fact of the matter is that when you set this system up and go to set the gain, you will be using sine waves at max amplitude...at least you will if you're listening for the clipped signal. You could get around that by using the meter method and Ohm's Law to find and set voltage output. By doing that you would use the speaker's rated RMS (not the amp power output) as your guide, so the gain will be set lower than it normally would be if you were setting it to hear the clipped signal. Thus, sure, it's reasonable.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

luckydevil

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Posted: May 25, 2006 at 8:43 PM / IP Logged

Thanks Stevdart.

I plan on doing just as you said and set the gain with the DMM.

Just to play devil's advocate though... what kind of wonderful things would I have to look forward to if I did use say a 1kw amp and then play a sine wave at full volume with a charging system that was no where near up to par?

Would it just drain the battery, or possibly kill the alternator?

stevdart

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Joined: January 24, 2004

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Posted: May 25, 2006 at 9:45 PM / IP Logged

I thought you were referring to a mismatch of amp power vs. speaker capability, but now I understand your concern. Will the alt be damaged if an appliance demands more than it can produce? Or if not the alt, the battery? It should be just the typical symptoms that are experienced when the power supply can't meet the demand. With the large power cable you'll be using with the sound system, the path of least resistance is to the amplifier. That starves the car's accessories that are also demanding current. Dimming headlights and all that.

The amplifier would also be starved, but the lack of sound volume is not apparent like the visual symptoms of the headlights are.

Eventually, it could kill the alt if it is making it work full throttle constantly...but it should never get to that point because the symptoms of the starved power will be annoying to the point that an upgrade would have to be made.

It sounds like this installation will probably not get to that point. Your friend may consistently use only 100 watts of that 1kW. If you guess that the alt has 30 amps available during a typical night-driving load, and figuring the voltage is sustained at 12.6 volts and allowing that the amplifier is 65% efficient, that would allow for about 250 watts from the sound system. You could have a load test done on the car to have a better idea of available amperage.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

luckydevil

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Posted: May 25, 2006 at 10:06 PM / IP Logged

stevdart wrote:

You could have a load test done on the car to have a better idea of available amperage.

I definitely plan to have that done just to be on the safe side.

Great info, it is much appreciated.

Any idea if there is a rough percentage (of alternator output) or number as far as how many amps are typically consumed by a car while driving/idling?

geepherder

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Joined: October 27, 2003

Posted: May 25, 2006 at 10:18 PM / IP Logged

Not much for the car to run, but you have to take into consideration your other accessories. Headlights, wipers, a/c, radio, power locks/windows, etc. I usually use a number around 25-40 amps to be safe.

My ex once told me I have a perfect face for radio.

luckydevil

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Joined: July 04, 2005

Location: United States

Posted: May 25, 2006 at 10:29 PM / IP Logged

geepherder wrote:

I just found out the factory alternator on the 2006 Jetta's is rated at 140 amps. So I guess that leaves me quite a bit of headroom considering he doesn't have navigation or any other fancy stuff.

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Current consumption with music

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