Turn off the car radio when you’re parked to save gas
June 27th, 2007 | by mbhunter |Is this a recent trend? A (usually) young male drives up to a store in his ride, parks, shuts off the engine, unrolls the window, cranks the volume on the radio, and goes in to buy something? As soon as a colleague at work mentioned this, I started seeing it all over the place.
It’s not just that the music is something I usually wouldn’t choose to listen to — though I wouldn’t mind if they cranked something I like once in a while! — but it wastes gas. Running the radio drains the car’s battery. When the car is started up again, the alternator spins and supplies the electricity to the car’s parts and recharges the car’s battery. But since the battery needs to be recharged more after blasting the radio, more current needs to flow to the battery than normal. Since more current is flowing, more torque is needed to turn the alternator’s rotor, because the electromotive force that opposes the motion of the rotor is directly related to the current flowing through the coils. This additional torque is supplied by — you guessed it — more gas.
Nothing can be turned on in your car for free. Air conditioning, radio, heated seats, power moon roof, DVD player — using all of these things ultimately makes the engine work harder, which mean that more gas is consumed.
Which costs you money, unless of course folks throw money in your open window because they think it’s a street performance.
17 Responses to “Turn off the car radio when you’re parked to save gas”
By Tyler on Jun 27, 2007 | Reply
This is the biggest load of crap I’ve heard from the liberal tree-hugging left to date! Unless you have subwoofers, amps, caps, etc. this will not be an issue. Instead of worrying about stupid crap like turning off your radio, how about SLOWING DOWN!!! Slowly accelerate, brake etc. Or maybe, just maybe, people actually drive the speed limit? Nah, I’m way ahead of myself because I need to turn off the radio before I actually slow down…
By anonymous on Jun 27, 2007 | Reply
I’m not sure if this post is meant to be humorous… I hope it is.. But just in case it’s not.
A gallon of gas contains enough energy, even given the inherent inefficiencies of the internal combustion engine, to move a 3000 pound car 25 miles down the road at a high rate of speed. Frankly, it’s astonishing when you really think about it.
I hope nobody buys that the draw of a car radio, which is vanishingly miniscule, is the appropriate place to save gas.
But if you do think that, here are a few more places you could save money
* Leave your headlights off until the last possible second (no need to waste gas by using headlights until it’s pitch black!)
* Unscrew all but one of your brake lights. Powering those superfluous brake lights is like throwing money away!
* Better yet, don’t use the brakes at all. Unless you have a Prius, using your brakes wastes momentum.
* Remove the sound insulation from the engine firewall. The car may be a little louder inside, but that stuff is heavy! Just think of the gas you’ll save.
By tinyhands on Jun 27, 2007 | Reply
Yeah, I’m afraid that while you’re technically correct, the amount of extra gas used is so negligible that we don’t really have the technology to measure it when there are so many other factors (namely driving style) to consider.
By Neely O'Hara on Jun 27, 2007 | Reply
It’s not about the money or gas savings: It’s about utter rudeness of these people who impose their loud music upon everyone else. I would never DREAM of blasting my music or talk radio or anything else so loud that other people were forced to hear it…And I would be humiliated if any kid of mine behaved so badly (even if the “kid” were 20-something).
I wonder if you could correlate this type of stupid selfish behavior to low earners — THAT would be the interesting data to see
By Nuvi? on Jun 27, 2007 | Reply
Alternator produces at a constant rate (supposedly, if it is not, your voltage regulator is shot) electricity as long as the engine runs.
So, it does not matter if your battery is full or half full or almost empty. It is charged at the same rate. If your battery is full, the energy from alternator is just converted to heat.
There is no way to make the alternator not produce electricity when the engine is running unless your alternator incorporates some sort of clutch system like the AC compressor which is unheard of (for alternator).
If you have a Prius, the gas engine is run for the sole purpose of running the alternator. So it does not make sense to talk about trying to disable the alternator while the engine is running.
By mbhunter on Jun 28, 2007 | Reply
Tyler: It’s not crap; it’s physics.
anonymous: Your suggestions are unsafe. People who blast their radios and aren’t even there to listen to it are wasteful. There’s no point to doing that.
Needy: Exactly!
Nuvi: So there’s no loss to charging the battery a little more? It’s just going to the battery rather than being shunted somewhere else to produce heat?
By CK on Jun 28, 2007 | Reply
Can I ask what part of the country this idiotic practice is happening in?
By flifla on Jun 29, 2007 | Reply
Wasting gas by leaving the radio on is like wasting energy by twiddling your thumbs
By Kurt on Jun 29, 2007 | Reply
I’ll admit that I thought this was a load at first. However, I failed to realize that alternators are smart enough to reduce the electrical resistance when the battery is topped off and therefore I suppose yes, officially this post is accurate. But then again, it’s also accurate to say that when you run west to east, you’re slowing down the rotation of the earth. I wouldn’t worry about that, and neither would I worry about the gasoline consumption of your radio.
By Kurt on Jun 29, 2007 | Reply
By the way, I thought this link was interesting:
http://www.halfbakery.com/idea/Car_20Alternator
By EMF on Jun 30, 2007 | Reply
Some of the ideas here gave me a chuckle, but then I’m an electrical engineer.
As a battery charges, its voltage increases. The output of the alternator is held at a constant voltage. No, they don’t “reduce the electrical resistance.” When the battery is charged, the current decreases. It’s the voltage AND the current that uses power. Just as in a totally empty house with no loads connected to the electrical system, there is voltage present but with no current draw by any loads there is no power consumed (except a little bit for the meter itself).
For the typical radio installed by the manufacturer, running it for a few minutes does not use enough energy to be really significant. If it were significant, then don’t used it while driving either. I agree with “anonymous” above that lights are a more significant consumer of power. I wouldn’t recommend following his facetious suggestions though, the ticket or accident would be more expensive.
On the other hand, some of these monster system use significant power. They have to add large capacitors because the power required for those base beats would overload the normal electrical system.
By wolfy on Jul 1, 2007 | Reply
Yes he is right. If you have ever taken a Physics class you will know
By crossn81 on Jul 2, 2007 | Reply
I think we should follow the suggestions of the post to the logical conclusion that we should drive our car with all the “extra” fuses unplugged. Unplug the interior lights, dash lights, power steering, and we should all sit in our cars with all the windows closed, and no a/c or heat turned on. This could be quite interesting in the sweltering summer heat and also in the freezing winter.
Oh, I forgot to mention windshield wipers!
By OhBrother on Apr 22, 2008 | Reply
Nuvi? and EMF got it right, and explained it best.
Your alternator produces the same amount of electricity to recharge the battery no matter what the battery’s charge state is, and does NOT work any harder when the battery is low. The alternator
only works while the engine is running, so there’s ZERO gas waste in using any electrical device while the engine is off. Even if you foolishly run the battery dry and have to jumpstart the car later, it
takes ZERO extra gas to recharge the battery from the alternator, because the alternator isn’t working any harder.
People like mbhunter and fifla should just be quiet. You people don’t know what you’re talking about.
By Tom on Jul 14, 2009 | Reply
Alternators produce constant voltage but the amperage does vary. Alternators are rated in output amps. An alternator on a vehicle with a fully charged battery is NOT shunting current. The voltage regulator senses the battery and if the battery is fully charged the regulator “turns off” the output from the alternator. The amount of horsepower needed to turn the alternator varies with the current load. That is to say, an alterntor prducing 20 amps to meet normal system demand will not require as much energy to turn it as an alternator running at full output to recharge a dead battery. Go to an alternator shop and watch them load test an alternator and you will see what I mean. (25 years in the alternator business)