When you turn the AC on, turn the speakers louder or turn on a subwoofer in a car, does fuel economy decrease in order to create more power?
In: Engineering
1 hp is about 750 watts. The alternator is in the ball park of 70 % efficient. Your AC compressor will take 2 or 3 hp mechanically from the engine. Take your electric load, divide by .7 and divide by 750, this is the load your placing on the engine.
A modern car engine will have a fuel consumption of .4 to .5 pounds of fuel per horsepower per hour.
This is the extra fuel your burning for accessories.
ETA: double checked my numbers, some new cars are getting fuel consumption down into the low .3s. Didn’t think they could go that low.
When you turn A/C on the compressor gets power from one of the engine belts. The compressor turning puts more load on your engine therefore reducing fuel economy. The stereo and subwoofer use electricity which is generated by your alternator. The alternator like the A/C compressor runs off an engine belt as well but the alternator is always running so the only way you could potentially lose fuel economy is if the stereo/subwoofer use enough electrical current to rob power from the engine’s ignition system (spark plugs). The A/C will definitely effect fuel economy, the stereo or subwoofer is debatable depending on how much electrical current is provided by the alternator.
Your engine ultimately powers everything in your car. So in a sense, yes. When electronics in your car pull more power, it has to come from somewhere, and your engine can only output so much power. However, unless you are running a lot of stuff over a long period of time, you really won’t notice much of a difference.
Everything in your car that consumes electricity can be evaluated in watts. Doesn’t matter if it’s a small LED or a 100 amp woofer, they all consume power in watts, and 745 watts is 1 horsepower. So a 100 amp woofer at 12 volts (if it’s truly pulling 100 amps) is using 1200 watts (1.6 hp) and it all has to be supplied by your engine. People with really large stereo requirements (my son) have to upgrade their alternator to compensate. To say it is supplied by the battery is disingenuous since your motor has to supply the battery through recharging.
Your audio system is belt driven. Also you have gasoline powered headlights and your tires need to be charges every day.
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