# Does your car produce "free" electricity? **URL:** \ **Category:** Factual Questions\ **Created:** [May 4, 2015, 5:03am UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210 "2015-05-04T05:03:34Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Procrustus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/procrustus/32/2994_2.png) [@Procrustus](https://boards.straightdope.com/u/Procrustus)\ **Post date:** [May 4, 2015, 8:51pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/21 "2015-05-04T20:51:39Z")
> [@Blue\_Blistering\_Barnacle](#): > > The fuel and lightbulb costs are very low. Even a minimal improvement in safety from keeping the lights on would (statistically) quickly outweigh efficiency losses and especially fuel costs. I agree. But even hypothetically, I always figured the car was producing more electricity than it needed, and therefore had a surplus I could use or not, for “free.” I guess what I’m hearing in this thread is that there is no free electricity in a standard ICE vehicle. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [May 4, 2015, 9:27pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/22 "2015-05-04T21:27:27Z")
> [@Procrustus](#): > > I agree. But even hypothetically, I always figured the car was producing more electricity than it needed, and therefore had a surplus I could use or not, for “free.” > > I guess what I’m hearing in this thread is that there is no free electricity in a standard ICE vehicle. This may be a fair question. Withoutasking for an exception to “the Second Law”, is it possible that the minuscule energy tapped by electronic devices would have been wasted anyway? That is, does hooking up the device cause any measurable \*additional \*load on the alternator? ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [May 4, 2015, 9:56pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/23 "2015-05-04T21:56:07Z")
> [@Blue\_Blistering\_Barnacle](#): > > This may be a fair question. Withoutasking for an exception to “the Second Law”, is it possible that the minuscule energy tapped by electronic devices would have been wasted anyway? > > That is, does hooking up the device cause any measurable \*additional \*load on the alternator? No, the amount of mechanical energy required to turn the alternator is directly dependent on the electrical load being placed on it. Given very small amount of current required to charge the phone relative to the amount of energy being produced by the engine, the “measurable” part might be problematic, but there’s no such thing as “surplus electricity” in the sense of current generated by the alternator that just vanishes off into the aether if it’s not used. One interesting implication of that is that regenerative braking on hybrids doesn’t work when the batteries are full. Another interesting example is that diesel locomotives use generator-based braking called “dynamic braking” but since they don’t have any way to store the energy generated they just have huge heating elements that exist for no reason but to place load on the generators. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [May 4, 2015, 10:48pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/24 "2015-05-04T22:48:24Z")
> [@GreasyJack](#): > > No, the amount of mechanical energy required to turn the alternator is directly dependent on the electrical load being placed on it. > > Given very small amount of current required to charge the phone relative to the amount of energy being produced by the engine, the “measurable” part might be problematic, but there’s no such thing as “surplus electricity” in the sense of current generated by the alternator that just vanishes off into the aether if it’s not used. > > One interesting implication of that is that regenerative braking on hybrids doesn’t work when the batteries are full. Another interesting example is that diesel locomotives use generator-based braking called “dynamic braking” but since they don’t have any way to store the energy generated they just have huge heating elements that exist for no reason but to place load on the generators. Some electric trains now use regenerative braking to put current back into the third rail. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 4, 2015, 11:04pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/25 "2015-05-04T23:04:14Z")
And even diesel locomotives often have a contact bar that can be raised to a catenary wire, which they do in some parts of the country. The diesel actually just runs a generator, with electric motors connected to the wheels, so there’s very little reason not to include a contact bar. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [May 5, 2015, 3:07am UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/26 "2015-05-05T03:07:04Z")
> [@bob\_2](#): > > This probably explains why people are so reluctant to turn their car lights on on the evening. This is actually quite common in China. People in their Audi A6’s don’t want to turn on their headlights at night because it’s more frugal to drive with them off. :smack: ---
**Author:** ![Stealth\_Bragg](https://avatars.discourse-cdn.com/v4/letter/s/4bbf92/32.png) [@Stealth\_Bragg](https://boards.straightdope.com/u/Stealth_Bragg)\ **Post date:** [May 5, 2015, 11:17am UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/27 "2015-05-05T11:17:43Z")
I had a BL Mini back in the 80s and it was only 1000cc. You could hear the tickover revs drop noticably when you turned on the headlights. Guess the power draw was more than 1% of engine output in that case 🙂 ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 5, 2015, 11:50am UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/28 "2015-05-05T11:50:02Z")
> [@Stealth\_Bragg](#): > > I had a BL Mini back in the 80s and it was only 1000cc. You could hear the tickover revs drop noticably when you turned on the headlights. Guess the power draw was more than 1% of engine output in that case 🙂 Cars with less powerful engines would obviously take a greater percentage of power for things like headlights. I suspect this also factors into why it is common to not to use them even after dark if they don’t need them Also in the US, with daytime running lights started to happen (and Canada mandated them), one complaint I heard was that it would cost more in fuel, and some have gone so far as disabled them for that reason so it’s not just a China thing. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 5, 2015, 3:29pm UTC](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210/29 "2015-05-05T15:29:10Z")
> [@Stealth\_Bragg](#): > > I had a BL Mini back in the 80s and it was only 1000cc. You could hear the tickover revs drop noticably when you turned on the headlights. Guess the power draw was more than 1% of engine output in that case 🙂 I had the main power lead from the alternator come out of its clamp and short across the headers. The resulting load on the alternator\* slowed the car down\*! (Then the ammeter started smoking behind the dash. Most impressive.) [Previous page](https://boards.straightdope.com/t/does-your-car-produce-free-electricity/719210.md?page=1)