Friday, December 4, 2015

The Science of Saving Gas

I try to waste as little gas as possible while driving. I had a few questions that I wasn't sure whether would save gas or not on an automatic transmission Toyota Corolla. This is the result of my googling. Please correct me if I'm wrong.

Q: Does it save gas to put the car in neutral at stop light: 


A: No. The engine still runs. Putting the car in neutral just makes the rpm higher and shifting gears wears out the transmission more.


Q: Does it save gas to turn off the heat while driving on the highway?


A: No. All it costs is the electricity to run the fan, which is negligible. (A/C will use more gas tho)


Q: Does using the car to charge mobile devices: (cellphone, laptop, tablet) cost more gas?


A: No. When the engine runs, it powers the alternator to generate electricity at the same voltage regardless of how much of it is being used.

That electricity is used by the car lights, power windows, on-board computer, etc. and the remaining charges the car battery. If you charge your laptop while car is running, the extra load is negligible, so the alternator doesn't use more gas, it just charges the battery slightly slower.

If you run your A/C, the thing will draw more current than normal, so the voltage regulator will increase current. the alternator becomes harder to spin, then the engine will need to work harder and burn more fuel.

Q: How long can I charge mobile devices while my car engine is off before the battery doesn't have enough charge to start the engine?

¯\_(ツ)_/¯

Turn the key to the notch just before engine ignition to turn on electronics, then turn it back one notch to the left. This turns off the car's appliances, but keeps the radio and charge ports active.

I left the laptop and cell phone charging for two hours and I could start the car no problem.
 
My laptop battery has maximum capacity of 34.873 Watt-hours (Wh). 
  • Acer Aspire 7750G - 6645
My phone battery: 7.98 Wh. 
  • Samsung Galaxy S3.
My tablet battery: 31.236 Wh. 
  • Samsung Galaxy Tab SM-T520.

unit conversion reminder: Watt-hour = Voltage x Ampere-hour

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