>Quick post on recharging electric cars

>I saw this in the comments section for a Washington Post Outlook section article on electric cars:

[W]e need to revolutionize our batteries. The Tesla electric car (which may or may not actually make it to production) is aiming for 300 miles between recharges, basing this upon new batteries, but we need batteries with that much or more range, but with rapid recharging: hopefully, no more than 15 or 20 minutes, max.

First, they are producing the Tesla Roadster (240 mile range, 0-60 mph in 3.9 seconds) in very small quantities.

Second, assuming 300 mile range and 150 watt-hours per mile, you’re talking about a 45 kWh battery. For charging in 20 minutes, that’s a 135 kW connection, which at 220 V for two-connector house current, you’ll need a 600+ Amp connection. As far as I know, you probably don’t want to be handling 600 Amp connections regularly. Even if you get the car down to bike efficiency (40 watt-hours per mile @ 20 mph*), that’s 12 kWh stored, and 36 kW connection, which is still a 150+ Amp connection at 220V.

We’re not going to be driving 300+ miles on electric cars and then recharging them in 20 minutes, unless you completely replace the battery while charged. These batteries weigh over 1000 lbs and have extensive heavy-duty electrical connections. They are usually custom-fit into the cars to provide the largest battery package that fits in the car. I don’t forsee a huge network of service stations (“Jiffy Charge”?) that will replace your multi-thousand dollar, 1000-lb battery in less than half an hour. I’m not saying it definitely won’t happen, I would just bet money against it.

Does this mean that without liquid fuels, the 1000-mile roadtrip day is done? The drive-around-the-clock coast to coast marathon?

*For 100W of output, you can ride a bike at 10mph, which is 10 watt-hours per mile. Scaling up to 20 mph and assuming that most of the losses are air friction, which scale with the cube of speed, that’s 8x as much power to go 20 mph instead of 10 mph. For 800W at 20 mph, that’s 40 Wh per mile. Since at 10 mph the power required is not all air friction, this probably overestimates the power required for 20 mph.


About perkinsms

I'm an engineer and father interested in transit, parking and economics.
This entry was posted in calculations, cars, efficiency, electric cars, energy, environment, gas, oil. Bookmark the permalink.

One Response to >Quick post on recharging electric cars

  1. Mark says:

    >The solution is obvious:We should power cars by blood sugar. You could just get in, stick a tube in your vein and one in your artery, and the car could burn your blood sugar.Boom. I’ve solved both the oil shortage and the obesity problem at the same time.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s