Saturday, January 25, 2014

what is stopping people from just replacing a gas engine with an electric engine?

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Q. What is stopping people from just replacing a gas engine with an electric engine. I know a little bit about cars but not enough to know this answer. What makes an engine go from 8000 rpm or so down back to like 1 or 2 thousand rpm when you shift gears. Could you do the same thing with an electric engine?
Where would i be able to look at find motors with the type of power a car would call for?


Answer
If you want the equivalent of a golf cart, there are companies that will make the conversion for you. It will cost you thousands of dollars and you won't be able to go from L.A. to Anaheim on a charge.

The biggest barrier is batteries.

Gasoline has an energy density of about 46.19 Newton-Meters per kilogram (energy units per unit of weight).

A lead acid battery (the cheapest kind) comes in at 0.11 NM/Kg. That means it takes more than 400 times as much lead-acid battery to get as much energy as the same weight of gas.

The next generation of battery, the nickel-metal-hydride (NMh) they use in most hybrids, has a better energy density, but it's still only twice as dense as a lead acid, or 200 times more weight for the same energy as gasoline. On an energy per cubic centimeter basis, it's a lot better, but still takes 100 times as much space per unit of energy.

The newest batteries, used in laptops and the all-electric Tesla sports car, are lithium-ion. An experimental Japanese sedan, the Eliica, with eight wheel motors and lithium-ion batteries ran 230 mph a few years ago, but it cost a fortune, and we haven't heard from it since. These batteries have an energy density by weight three times that of an NMh, and 5 times by volume. So gasoline is only18 times as dense by volume. Still, imagine having to find room for 18 gas tanks in your car!

As to gears, you need gears for mechanical advantage (like a lever) to allow the engine to remain in its most efficient operating range at varying speeds.

Most gas engines do their best work between about 2,400 rpms and 5,000 rpms. A high performance engine's range will be higher, but they all need gears, or else they either couldn't get going from rest (geared too high) or would run out of breath before they reached freeway speed (geared too low).

If you ever rode a ten-speed bike, you'll know that you need low gears for going up hills and high gears to keep up with the pedals going down. Same with a car.

the Tesla now has only one gear. That's because an electric motor produces its maximum torque (the force to move the car) at zero rpms (from a dead stop). If you want one, they are taking deposits. They only cost around $100,000.

BTW, if you want to avoid sounding uninformed, technically the electric unit is called a "motor" while the internal combustion one is called an "engine." It's an engineering distinction.

Which commute bicycle is best for me?




Tara


I am looking for a bicycle for a commute to work of about 8-10 miles and would consider an electric model. Can anyone offer any specific models? There is so much out there to choose from. The area where I live can be fairly hilly, so higher number of speeds would be best, and I'm wondering how often there would have to be battery replacement on an electric bike. Any help would be appreciated, preferably from personal experience, but speculation from an experienced rider would also help. Thanks.


Answer
You can get a good electric assist bicycle - for a few THOUSAND dollars. http://www.trekbikes.com/us/en/collections/electric_assist/models/ Or...you could take the initiative to get a nice entry level "performance hybrid" with the gears to pull hills under your own power. And this bike may just come factory equipped with fenders & a rear rack for under $400! You will get & stay fit. Electric assist bicycles make you fat & lazy. What if the charge in the battery runs low or out at the wrong time & in the wrong place? Then you are faced pedaling an extremely heavy bike home under your own power. See these two links...

http://www.rei.com/product/826111/diamondback-insight-rs-commuter-bike-womens-special-buy
http://www.rei.com/product/826110/diamondback-insight-rs-commuter-bike-special-buy




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