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Wednesday, July 29, 2009

Electric Cars and the Ultimate Battery

I was reading an article today on "The Oil Drum" called

Who Killed the Electric Gas Tank?

This article called about EEStore's super capacitor battery replacement. They are still working on it and it is controversial whether or not it can even work. It supposed to be about 52kwh at 3,500 volts. It is supposed to be charged in about 3 to 6 minutes. A couple of thoughts occurred to me.

First, they say we need 50kwh of power to get the range that everyone is used to - about 300 miles or so. Most electric cars today get somewhere between 60 and 120 miles on a charge. It isn't good to fully discharge lead acid batteries, so most home built electric cars could possibly go up to 120 miles, but the owner minimizes the trip to half that so that the battery life is extended. But, be aware that most people are fine with short trips per day. The average commuter drives about 30 miles a day. So, my question is, do we really need that kind of range? If we do, we could take a bus, train or a plane. Are we so spoiled that we just have to have a 300 to 400 mile range? Or is it just the brainwashing from the media that constantly compares electric vehicles to their gasoline alternatives?

The second thought was the amount of time to fill up. The assumption is that people wish to fill up their electric vehicle in the same time it takes to fill up a typical fossil fuel car. That changes as well. A big SUV takes longer than a Honda. And a small diesel car can take longer than a suv. That is because the diesel is foamy and topping it off gets pretty slow. But lets say the average is 3 minutes. The EEStore seems to shoot for that goal. So, that is 52, 000 watt hours from empty to full in 3 minutes. I don't know about you, but that struck me as a lot of power in a very short amount of time. If you did that charge in one hour from a 240 volt outlet, then that would take 52,000 watts of power at 240 volts and 216 amps. Most houses are setup with 200 amp service, so that wouldn't work. If you did that same charge in 3 minutes, or 20 times faster, then it would take over 4,000 amps. NOT GOING TO HAPPEN!!!

But, let's say that you only needed a 140 miles or less per day and you needed to top off the super capacitor at 24,000 watt hours. If you had 100 amps free to use in your house, then you could top it off in 1 hour, or a little over 2 hours for the full 52kwh capacity.

Most electrics drive maybe 60 miles a day tops and need about 10kwh up to 15kwh to replace that charge. Charging from any 120 volt socket, that takes about 7 to 10 hours. From a 240 volt socket rated at about 20 amps then you could charge that in about 2 to 3 hours.

But, assuming you need to top off the super capacitor at your house from empty to full and use that same 20 amp 240 volt circuit, it would take over 10 hours. So, the fast charge may not be an option, although a battery swap program would work pretty nicely.

Don't get me wrong, I like the idea of super efficient and cheap batteries. I just want to see very light weight vehicles and/or bikes and trikes for daily commutes. Something small like this could charge very quickly because there is nowhere near 50kwh of storage in it. A 24 volt bike battery with 10 amp hour batteries only holds 0.24 kwh. That means you could fill that size super capacitor 200 times faster. So, a super battery for the bike could be charge in 3 minutes, but not a big one for a car that gets 300 mile range. (Unless you get powered up at the nearest power plant)

Super batteries are nice, but striving for the ultimate 3 minute quick charge, while possible, is not at all practical. Probably the best you could hope for at a filling station is to get 10kw at a time. After 10 minutes of that, you only have about 1.7 kwh of charge, or about 6 miles worth of driving. (If 5 people charged at the same time it would be about 50,000 watts at about 200 amps.) And 6 miles for charging every 10 minutes isn't that great. Even if they double the power available to 20,000 watts, you are still looking at 2.5 hour charge time. If you went to 50,000 watts of power available then it would still take an hour to charge and only a few people could fill up at a given time.

It reminds me of Ean from the first Jurassic Park movie, "Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."

Richard

2 comments:

  1. i dont think they were shooting for 3 minute charge from the house, i believe in their documentation it states it CAN be charged in 3 minutes, *pause* it can also be charged from a normal wall socket, i dont think they put the 2 together

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  2. On the Zenn site it says •EV Charging time (full) - 100% charge = 3-6 min
    This leads people to think it can be done in 3 to 6 minutes. And technically it can. But not in any real world scenario - ever. Just imagine pulling up to a filling station and them giving you access to 2,000 to 4,000 amps at 240 volts. Or up to 1 million watts of power for 3 minutes, or half a million for 6 minutes. And they still have other customers as well. It is just marketing spin. They say it can charge that fast, and then on the same page they say it can be charged from a regular outlet. They are correct, but my point is that it is misleading.

    Richard

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