# How much power can my car provide?



## ozzynichols (Feb 19, 2010)

I would like to know how much current I can safely draw from my 2005 Hyundai Elantra's electrical system for planning my system. I know idle and cruising speed are different. I'm not a bass head, so not to many big power gulps. Thanks.


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## stbanas925 (Jul 18, 2010)

it depends on what size your alternator is. considering its a small car probably around 80amps. thats good enough for around 500 watts rms. you might have a dimming problem at idle though. You should do the big 3 upgrade.


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## tmcdade (Jul 4, 2009)

I just did a quick search and it looks like your car has a 90 amp factory alt. I think it's going to depend on how much stuff you're running, like HID headlights will take a lot of power when they're first turned on IIRC. It's also going to depend on whether you crank the volume up all the way or not

You got me thinking so I did a search and found some interesting stuff:

"As audio output goes up, so does the energy required to produce the sound waves. It takes about 16 amps of electrical power for every 100 watts of audio output. If a vehicle is equipped with a 100-watt amplifier, the stock alternator can therefore easily handle the 16 amps needed to power the sound system. But if it has a 500-watt system, it will pull more than fives times as much juice from the charging system (80 amps) when the driver cranks up the volume. At that level, the load may exceed the amp rating of the stock alternator. If the vehicle has a 1,000-watt system, the charging system will have to produce 160 amps to keep the decibels pumping - which is way more than any stock alternator can produce.

It takes power to make power, and for every 25 amps that an alternator produces, it saps about one horsepower from the engine to drive it. A stock 100-amp alternator running at maximum output will need about four horsepower from the engine. If the vehicle is equipped with two or even three high-output 200-amp alternators, the charging system may need 18 to 24 horsepower at peak output.

Another rule of thumb is that alternator output should equal about 25 percent of total battery capacity. A dBA racer with a 400 amp-hour battery pack would need at least a 100-amp alternator to keep his batteries charged. For continuous charging, the alternator output should be 150 percent of maximum load." (High Output Alternator)


And some more good reading here: 
Say you have a 1,000-watt audio system and you want to know if your car's electrical system can drive it. At full output, the system will produce 1,000 watts of power to your speakers at about 62 percent efficiency. This means that the input power to the amplifiers is 1,000 / 0.62 or 1,612 watts. The standard equation for power is

P = V x I

where P is input power in watts, V is input voltage, and I is input current in amps. If we assume that the battery's voltage is the typical 13 VDC, then the input current, or alternator power, required by your system can be calculated from the above equation. Rearranging the equation, we get

I = P / V

By plugging in the numbers and solving the equation, we get I = 1,612 / 13 – or 124 amps.

Most stock alternators produce only about 60 amps maximum. Of this, about half is used to run the car itself. So this leaves you with about 30 amps for your system, 94 amps less than the 124 you need. Where will the other 94 amps come from? The battery will try to supply it, but it will be able to do so only for short periods before the voltage drops to an insufficient level. Your system will not be able to play at its full potential for any significant length of time. (Upgrading Your Electrical System)

So if I understand everything correctly and did my math correctly, that means that if you want to leave your alternator with enough power to run the car, you could use up to a 350 watt amp. That's if you ran it w/ the volume at max and the amp puts out what it's rated for. Now if you only ever turn the volume up half way, then you could probably get away with a larger amp.

That said, I've read about people running 1000w amps off of 90A alternators, but I have to wonder if it isn't really stressing their alternator.

Sorry I made this so long, you probably wanted a simple answer. But hopefully it helps a little

Edit: A Big 3 upgrade would probably be a good idea too. Can't hurt


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## MarkZ (Dec 5, 2005)

The problem with this kind of analysis is that music is transient, so all those numbers and equations go out the window! Think about this ... lots of people here run stock alternators and 1000-1500w of amplifier power. It still works. 

Remember, when you choose an amplifier, what you care about are peaks, not average power content. If you know your peaks are going to be 100w, then you choose a 100w amp. That doesn't mean that your amplifier is producing 100w all the time or drawing 16A all the time. It just means that during maximum draws it will draw 16A. Where will it draw that 16A from? Not necessarily all from the alternator and battery... it will draw its current also from the internal reserves, and will charge those internal reserves when the transient is finished.

Here's something that might blow your mind... Your 100w amp may only be producing 10w at max volume averaged over the length of the whole song! That means that the average current draw would be 1.6A instead of 16A. Note that the key word here is _average_.


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## oslouie (Jul 6, 2010)

I'd upgrade the battery and go from there. IMO, it's more important to have a good reserve. The alternator only charges the battery, but I'm one of those people.


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## kyheng (Jan 31, 2007)

Grab yourself a Pioneer amp's manual and read it properly. It will state clearly on the typical and max current draw. Typical is what you need to see(well, same as what MarkZ has said basically)


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## ozzynichols (Feb 19, 2010)

Thanks for all the info guys!


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## sqshoestring (Jun 19, 2007)

I would guess you could run 1kw total and not have much problem until you really lean on it. I had a kicker 700.5 in my car with a 125A and it dimmed a little at idle with AC and everything on, and it idles slow, but just enough to notice really. That was 420rms on subs. I clamped it 74A peak on bass music clipping subs and highs clean, and it had 40A or less average (rms amperage) at the same time, and I'd never play it in real use that hard. Since my subs were rated for 600rms I let it wang just to see what it would draw. Car was running everything else was off, had a newer stock size battery with a 5ga amp kit. I bet you will be fine at 500rms on subs that matters the most. Like posted lot of people run 1-1.5kw and just don't flog it at night. Amps draw on a log scale so they will take much less power at 75% output than 100%. It will be hard on the alt if you hammer it a lot.


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## ozzynichols (Feb 19, 2010)

I understand the benefit of using larger than necessary amps for the purpose of headroom, but (based on what your saying about the log scale) it looks like using larger amps could actually help achieve the same output with less current draw because they aren't working as hard. That is very helpful.


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## MarkZ (Dec 5, 2005)

ozzynichols said:


> I understand the benefit of using larger than necessary amps for the purpose of headroom, but (based on what your saying about the log scale) it looks like using larger amps could actually help achieve the same output with less current draw because they aren't working as hard. That is very helpful.


No, that's not what he meant. Actually, a higher power amp is generally going to draw more current than a lower power one, even when they're outputting the same. The exception to this rule would be class D and class G amps.


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## ozzynichols (Feb 19, 2010)

Ah... I, see.


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## gijoe (Mar 25, 2008)

oslouie said:


> I'd upgrade the battery and go from there. IMO, it's more important to have a good reserve. The alternator only charges the battery, but I'm one of those people.


The alternator does more than charge the battery, it runs the car. Disconnect your battery when the car is running and it will stay running. The battery is there to start the car and to provide extra power when the system is using more power than the alternator is providing, keeping the accessories working and your car running when the motor is only idling. 

Having said that, upgrade the ground wires and the battery. For most systems this is all you'll need. After that you'll know if you'll need a high output alternator.


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## ozzynichols (Feb 19, 2010)

I already upgraded the grounds from the neg batt and engine block at the the alternator. I just want to make sure I won't have to upgrade the alternator because I'd rather not spend the money for a car that has 70k miles on it, and I'm not sure there is a bolt on upgrade for my car.


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