1. Subscribersonhouse
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    20 Aug '11 03:54
    http://www.physorg.com/news/2011-08-energy-storage-device-recharge-electric.html

    I did a quickie analysis and figured this: suppose the battery stores 25 Kwh of energy.
    Suppose you want to charge that battery in one hour. That means pumping in 25,000 watts for a full hour. But suppose you want to charge it in 30 minutes. Then you need 50,000 watts running a half hour. But suppose you want to do it in 3 minutes. Now you need 500,000 watts running for 3 minutes to get that 25 kwh battery to peak.

    So how do you do that? Run 500 volts, you need 1000 amps. 100 volts, 5000 amps.
    So it looks like, in order to keep the cable under the size of a 2X4, you have to way up the voltage, say 5,000 volts at 100 amps. 50,000 volts at 10 amps. Something like that.

    So what technological answer is there for such a charging station?

    Also, am I correct in my assumptions here? Anyone want to think this one through and see if they come up with the same problems?

    I know how we insulate at 50,000 volts, I work with 200,000 volt power supplies and it ain't easy, especially for public use. For geeks like me, we are used to that kind of energy, and we know how to handle it, buddy system kind of thing but most of the cables we use only insulate around 30,000 volts. And if that cable got a crack in it somehow and a little bit of moisture, say a rainstorm......

    So high voltages in public hands? I don't think so.

    So how high a voltage could we build a power cable, to be flexible and robust enough for public customers to handle safely? We could do 5000 volts at 100 amps.

    Even that can be extremely dangerous if a crack in the insulation showed up.

    So it sounds like the cable is going to have to be a pretty complex affair, say a double insulated or triple insulated cable with conducting coatings inside or like coax with several coaxial layers and the outer layers having sensors that detect the presence of current flow that would indicate leakage, like a ground fault indicator but for 5000 and up voltage systems.

    Even then you have to explicitly trust the current leakage sensor to work almost 100 percent of the time the cable is in use.

    Assuming such a battery comes online there is going to be serious issues trying to cram that much energy into a short space of time. Anyone want to verify my analysis?
  2. Joined
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    20 Aug '11 11:39
    And on top of that cables carrying large currents tend to be very
    vulnerable to induction heating if coiled at all.

    You would be very likely to get many of the cables catching fire
    due to improper use up past 15 amps or so.

    the best bet would probably be quickly replaceable batteries,
    so you can leave one at home on charge and use the other.

    However as batteries of this size are heavy people would need
    special equipment.

    this is one reason why people talk about underfloor induction,
    as you can have professionals install the stuff in the floor where
    the users can't get at it and mess it up.
  3. Subscribersonhouse
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    20 Aug '11 11:52
    Originally posted by googlefudge
    And on top of that cables carrying large currents tend to be very
    vulnerable to induction heating if coiled at all.

    You would be very likely to get many of the cables catching fire
    due to improper use up past 15 amps or so.

    the best bet would probably be quickly replaceable batteries,
    so you can leave one at home on charge and use the other.
    ...[text shortened]... e professionals install the stuff in the floor where
    the users can't get at it and mess it up.
    Underfloor induction? You mean those new matched frequency resonant coil jobs they talk about for charging cell phone and laptops from a meter away or so? I thought those devices were transferring a hundred watts or so. I haven't heard of any high power devices.

    Underfloor induction would still have to transfer massive amounts of energy, if it were magnetically coupled.

    It sounds like it would be a lot safer though. If you have a recharging station and you drive up and it connects coils underneath it wouldn't have the problem of high voltages.

    Of course if you had something like that where you drive up, stop the car above a charging station, the connection could be high voltage, but I would want to get out of the car for the time it charges! Although you would be somewhat protected by the faraday effect, because of the way bodies are constructed, parts are not welded together so voltage differences can build up between body parts if there was a high voltage on the frame.

    I know about that stuff because of my mobile ham gear. There are guys running a kilowatt transmitter inside their car (I run 100 watts max) and they have to go to great lengths, like welding grounding straps from the doors to the frame and from frame section to frame section to keep spark plug noise out of the receiver and to keep rf out of the car's computer and other electronics.

    All in all it sounds like a lot of engineering needs to be done to get that kind of energy transfer to car batteries, like 500 kw for 3 min.
  4. In your face
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    21 Aug '11 11:49
    If there is a need to charge these cells in such a short period of time, why not just have charging stations operated by qualified persons. Then the risk is taken out of the hands of the average careless person, capable of inflicting a multitude of mischieves upon themselves.

    Another solution would be perhaps have a store that swaps discharged cells for fully charged ones. These would not have to be charged very quickly as a buffer could be built up, based on demand.
  5. Joined
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    21 Aug '11 12:22
    better yet use hydrogen and fuel cells and refuel as fast as a petrol car.
  6. In your face
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    21 Aug '11 12:58
    Originally posted by googlefudge
    better yet use hydrogen and fuel cells and refuel as fast as a petrol car.
    I've always been a bit concerned about those things going 'pop' in a crash situation. How safe are they?
  7. Cape Town
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    21 Aug '11 13:36
    Originally posted by jimslyp69
    If there is a need to charge these cells in such a short period of time, why not just have charging stations operated by qualified persons.
    Because it would drive up the cost considerably.
  8. Cape Town
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    21 Aug '11 13:37
    Originally posted by googlefudge
    better yet use hydrogen and fuel cells and refuel as fast as a petrol car.
    Hydrogen fuel cells are little more than a US ploy to try and delay the coming of the electric car.
  9. Standard memberSoothfast
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    22 Aug '11 08:31
    Originally posted by googlefudge
    And on top of that cables carrying large currents tend to be very
    vulnerable to induction heating if coiled at all.

    You would be very likely to get many of the cables catching fire
    due to improper use up past 15 amps or so.

    the best bet would probably be quickly replaceable batteries,
    so you can leave one at home on charge and use the other.
    ...[text shortened]... e professionals install the stuff in the floor where
    the users can't get at it and mess it up.
    Replaceable batteries make sense. Go to a "recharging station," it takes the drained battery and puts in a charged one. It is then not necessary to figure a way to safely charge a battery in the time it currently takes to fill a tank with gas. Such stations would largely charge their stock of batteries during the nighttime when residential and commercial electricity demand is lower.

    Naturally it should still be possible to charge a car at home as well by plugging it in overnight.
  10. Joined
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    22 Aug '11 11:21
    Originally posted by jimslyp69
    I've always been a bit concerned about those things going 'pop' in a crash situation. How safe are they?
    *Shrug* How safe are petrol tanks? Safe enough for us to ignore their danger. If you tried to introduce them today, Elfin Safety would be on top of you like a ton of bricks[1]. With proper use, well... my car has yet to explode violently. Urban myths about cell phones making them go klablooie have been disproved more than once. Petrol stations, and petrol tanks in cars, are theoretically highly volatile. In practice, the most dangerous part of tanking petrol is probably when you turn back into the road with your full tank and get side-swiped by crossing traffic.
    I find it hard to believe that hydrogen tanks are going to be so much more dangerous than what we already have. For one, hydrogen is, yes, very flammable, but it's also very, very light. It'll go upwards. Petrol fumes stay around.

    Richard


    [1] In itself a real danger, tons of bricks on your top. But Elfin Safety never seems to realise this, as it's not in their portfolio.
  11. Joined
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    22 Aug '11 11:23
    Originally posted by twhitehead
    Hydrogen fuel cells are little more than a US ploy to try and delay the coming of the electric car.
    On the contrary - heavy, slow-charging battery-run cars are little more than a Japanese ploy to delay the coming of the hydrogen car.

    Richard
  12. Cape Town
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    22 Aug '11 11:31
    Originally posted by Shallow Blue
    On the contrary - heavy, slow-charging battery-run cars are little more than a Japanese ploy to delay the coming of the hydrogen car.

    Richard
    I guess you must work for one of the US companies wishing to perpetuate the myth.

    If I could afford to import an electric car from China, I would do so today. I would probably never buy a hydrogen car because they do not solve any of the problems that fossil fuel cars already have. As I said, they are little more than a US ploy to distract people.
    I am yet to see anyone other than the US, interested in a 'hydrogen economy', I have never seen a good argument for introducing such an 'economy', and I have seen good arguments for electric cars and good explanations for why the US doesn't want them.
  13. Joined
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    22 Aug '11 11:32
    Originally posted by twhitehead
    Hydrogen fuel cells are little more than a US ploy to try and delay the coming of the electric car.
    wow, my cynicism meter just exploded ;-)

    Actually both cars are electric, so the distinction is battery vs fuel cell.

    Batteries are heavy, hard to charge, and approaching the limits of how
    much power they can store, thus limiting further development.

    Hydrogen fuel cells on the other hand give the potential for much greater range
    and power output.

    Now while it is true that hydrogen is flammable and potentially explosive...
    So is petrol, and unlike petrol hydrogen is very lightweight and so has a tendency
    to blow away, rather than pool and collect.
    So while safety is an issue, its not a crippling one.

    I would also point out here that batteries have been known on occasion to catch fire,
    and explode, and unlike hydrogen that simply burns giving off heat and oxygen,
    batteries can contain excitingly toxic and corrosive chemicals.

    Batteries are also a pain to recycle, and require lots of energy to make and recycle.

    Fuel cells also can be hard to recycle, but they last longer, much longer, than batteries.
    and the fuel they use is very easy to recycle.


    Basically they are both systems for storing energy for re-release.

    I would put my money on the long term success of hydrogen over the battery.

    The short term advantage for the battery car is it requires less infrastructure.

    But that won't save it in the long run as batteries knock up against limits of design
    while fuel cells still retain room to improve, from a better starting position.
  14. Cape Town
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    23 Aug '11 06:25
    Originally posted by googlefudge
    Actually both cars are electric, so the distinction is battery vs fuel cell.
    I am totally uninterested in which is more explosive, or how the car actually works. The important things are:
    1. Distribution.
    2. Overall efficiency.

    Where is your hydrogen coming from? Is it generated using electricity? Is it generated at the charging stations, or at a hydrogen plant and then distributed via pipes and tankers etc? Is the generation of hydrogen then reconversion back to electricity in a fuel cell, more or less efficient than a battery?
  15. Subscribersonhouse
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    23 Aug '11 10:25
    Originally posted by twhitehead
    I am totally uninterested in which is more explosive, or how the car actually works. The important things are:
    1. Distribution.
    2. Overall efficiency.

    Where is your hydrogen coming from? Is it generated using electricity? Is it generated at the charging stations, or at a hydrogen plant and then distributed via pipes and tankers etc? Is the generation ...[text shortened]... gen then reconversion back to electricity in a fuel cell, more or less efficient than a battery?
    Fuel cells, at least as far as I know, can never be as efficient in the use of energy as batteries, which clock in better than 90% in the use of the energy given it. Fuel cells are ticking out around 40-60%.

    So the entire H2 economy, although clearly it is workable, would by no means be as efficient as batteries.

    That said, you have to get the electricity to store in batteries somewhere, the two are separate issues.

    You can generate H2 from solar energy using catalysts and such and I see signs of higher efficiency there every week.

    I also see work done on batteries that charge in minutes, although I have done some back of the envelope calculations showing it is going to be very difficult to actually get that much energy in a transportation battery any time soon, even given the ability of said battery to charge quickly. That alone introduces a whole new level of problems.

    I see references every now and then of PV cell incorporated into paint. That would be a real breakthrough IMHO. That would open up possibilities for electric vehicles to recharge themselves in the daytime when the owner is at work. I would expect the first gen of such devices to be not so efficient but when the engineering work gets in high gear, lets say in 20 years they get the efficiency up to 40 or 50%, the car would stay cooler inside and the battery would be being charged at a low rate with no connection to a source needed.

    Of course that doesn't help if you are in cloudy winter days and such so several alternative charging systems would be necessary but clearly PV paint would alleviate the energy situation to some extent at least.
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