I was heading off in my car for a short trip and threw in my tablet, but noticed that it wasn’t fully charged. Realizing there was an appropriate plug-in in the car, I decided to charge the tablet. By the time I reached my destination about four hours later, it was fully charged.
That got me to thinking, if it doesn’t cost anything to charge it, then why don’t I use my car to charge all of my various electrical devices.
So does charging a device hinder the output of the engine, or is the device using excess electricity?
Btw, most of my driving is at highway speeds.
Any electrical load increases fuel consumption. I recall reading about someone working out the math with fuel cost for an average car and finding it was slightly cheaper to charge off the grid.
This doesn’t surprise me. The electrical systems in cars are built for charging the car battery (in addition to running accessories), but they can get away with being less efficient just because the vast majority of the fuel is for running the engine. In comparison, no one’s going to care about the efficiency of the electrical output. Even so, it’s only worth it if you have all those electrical devices in the car anyway, and you’re going to be driving anyway when you need to charge all those devices. If you use your alternator (generator) to charge those things when the car is at home not being used, it’s probably going to cost even more than just using the grid.
Either way, of course, it isn’t “free.”
Actually, it would be pretty easy to produce free electricity in a car.
All you need is a big fan on the roof to take advantage of the wind the car creates. The fan would charge a battery, which would in turn produce hydrogen from a tank of water, and that would in turn power a turbine to produce electricity.
Better yet, you then can use said electricity to power a backwards-facing propeller, which then eliminates the need for a gas-powered engine to begin with. How does free transportation sound, my friend ? That’s the dirty little secret GM doesn’t want you to know, but I can provide the relevant schematics for the low low price of $19.99 ! Call now !
What you need to do is only plug your devices in when you’re going downhill. The added load to the alternator will add to the engine braking effect and help slow the car down.
Waitaminnit. Let’s take a really simple case, where there are no accessories in the car at all. The engine is making the car move, and it is also recharging the battery, and that’s all.What happens when the battery becomes fully charged? Is the engine’s mpg now slightly better because none of its power is going to the battery?
The car is still consuming electrical power, sending sparks to the plugs, the computer that controls the car, electric fuel pump and injectors, dashboard indicators, etc. But yes when the battery is at a full charge the amount of power that they alternator produces is less, and is also easier to turn. This is accomplished by a voltage regulator (either as part of the alternator or a separate unit) which meters out how much power goes into the electrical system.
The electrical power in a car comes from the alternator. The alternator generates polyphase AC power which is then rectified into ~14 volts DC. The alternator is able to generate power because the engine is spinning the field windings inside the stator via a belt drive. Any additional load you put on the electrical system (e.g. charging your tablet) means the engine has to spend more power- thus more fuel- to spin the alternator. A tablet may draw little enough power where you won’t be able to notice its effect on fuel economy, but it certainly isn’t “free.”
When you draw less electricity from the alternator, it takes less power to spin it. You can even draw negative electricity from the alternator to make it spin by itself! That way, you can do away with that messy internal combustion engine altogether.
got it! thanks!
even better is free motion altogether.
i saw an L and H documentary where they used a big magnet to get pulled along. they drove around town like that.
This probably explains why people are so reluctant to turn their car lights on on the evening.
You could do it with regenerative braking. That’s essentialy free electricity that is otherwise lost in the form of heat.
My father once told me to turn off my lights during the day to save fuel. I still have a hard time believing the load on the engine would change much by having the lights on.
It’s minuscule.
well, halogen headlamps are typically 55 watts each, so ignoring other losses it takes an additional 0.15 hp from your engine to power them.
It takes about 15 horsepower (at the wheels) for a mid-size sedan to cruise down the highway at 55 MPH, so you’re talking about an increase in power demand of 1%. When it comes to assessing fuel economy - especially outside of a laboratory - that’s at the level of noise.
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.
Safety info
"Safety performance[edit]Numerous studies done worldwide since the 1970s have tended to conclude that daytime running lights improve safety.[2][3][4] A 2008 study by the U.S. National Highway Traffic Safety Administration analysed the effect of DRLs on frontal and side-on crashes between two vehicles and on vehicle collisions with pedestrians, cyclists, and motorcyclists. The analysis determined that DRLs offer no statistically significant reduction in the frequency or severity of the collisions studied, except for a reduction in light trucks’ and vans’ involvement in two-vehicle crashes by a statistically significant 5.7%.[5]
Effect of ambient light[edit]The daytime running light was first mandated, and safety benefits first perceived, in Scandinavian countries where it is persistently dark during the winter season. As ambient light levels increase, the potential safety benefit decreases while the DRL intensity required for a safety improvement increases. The safety benefit produced by DRLs in relatively dark Nordic countries is roughly triple the benefit observed in relatively bright America.[2]"