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Charging physics confusion

Discussion in 'Technical' started by just-an-allusion, Dec 21, 2008.

  1. just-an-allusion

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    #1 just-an-allusion, Dec 21, 2008
    Last edited by a moderator: May 19, 2009
    Additional Moderator's Note: just-an-allusion turned out to be a troll writing semi relevant nonsense for the purpose of causing confusion. Though his posts are junk, some may find the responses useful. This thread remains for that reason.


    Moderator's Note: moved from this thread.

    So...why not merely produce and distribute a switchable (to match available power source wattage) power inverter with power doubling/multiplying circuitry to step up or down the available power to match the Tesla's battery requirements?

    You know, essentially the same circuitry setup that portable generators and DC to AC power inverters have, then you could truly plug in pretty much anywhere.
     
  2. graham

    graham Active Member

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    If I understand it correctly, this is essentially what Tesla has done. The charger/inverter is on board the car as part of their Power Electronics. The "mobile charger" is pretty much an extension cord, where the car itself adjusts to the amperage it is given. The home-based fast charger is really not much more than a fancy extension cord made to go to a 70 amp circuit with a bit of safety circuitry. All the intelligence of the charger live in the car already and can deal with a myriad different power outlet scenarios.
     
  3. just-an-allusion

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    If this be the case, then why not merely outfit the car with a large gauge charging cable (something in a bag to throw in the boot) or, if you really wanted to wax all self-sufficient and techie, how about outfitting the car with a retractable charging cord accessible out of it's rear panel or bumper (like with a trailer connector for towing) behind a spring-loaded, surface-flushed, panel?

    That would eliminate the need for a charging port on the "B"-pillar to plug a cord into/onto. Talk about "user friendly"....
     
  4. graham

    graham Active Member

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    I think you have pretty much described the "mobile charger"
     
  5. malcolm

    malcolm Active Member

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    #5 malcolm, Dec 22, 2008
    Last edited by a moderator: Dec 23, 2008
    Yep

    Doug posted some images of it on this very thread.

    Big yellow thing.

    You can't mis....

    Ah.....yes

    To be fair, I don't think it comes with a bag, just a box.

    Moderator's note:
    moved from another thread
     
  6. just-an-allusion

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    The Tesla itself should be equipped with an on board inverter/power doubler to step up (or down, as the case may be) the available wattage/amperage to that required by the Tesla's battery pack accordingly.

    The omission of such technology would amount to oversight on behalf of the Tesla's engineers...an issue which should be (hopefully) addressed within the immediate future.
     
  7. just-an-allusion

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    If this is, indeed, the case, then why has there been so much debate over the "need" of establishing a charging/recharging infrastructure...You know, when any outlet/power supply would do?
     
  8. shark2k

    shark2k Member

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    I think the reason is because through the media or just because of people holding onto the notion of refilling your car in less than 5 minutes with gas. Because of this, people want still think they need to be able to charge the car fast and that is what a charging/recharging infrastructure would allow. It would more easily be able to allow for the quickest charge possible. Using any outlet/power supply with the mobile charger, you are limited to 120v (and how ever many amps go along with that). That is just my $0.02 though.

    -Shark2k
     
  9. graham

    graham Active Member

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    Any outlet or power supply can technically be connected to the Roadster (given the proper adapters if the plug doesn't fit), but a 15 amp outlet can take >30 hours to do a full charge and a 70 amp outlet can do a 3.5 hour charge. Theoretically the Roadster can handle higher than 70 amps if such outlets were available. It is easy to see where people would like more current than less, even if less will technically connect.
     
  10. just-an-allusion

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    The point of my question(s) that I believe the two of you are missing is that while it's obvious that the so-called "quick charge" power cord incorporates a transformer in the rather large plug end to convert the incoming AC amperage to DC voltage suitable for recharging the on-board batteries (as does any typical laptop power cord), I am questioning why doesn't the Tesla, itself, have an on-board, or even in-line (though an on-board converter would be more so aesthetically appealing, practical, and less cumbersome than an in-line converter), step up converter to automatically increase whatever incoming voltage/amperage to the amount desired for "quick" charging?

    Understand now?
     
  11. JRP3

    JRP3 Hyperactive Member

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    I think you're missing some basic physics here. No matter what Tesla has onboard, if the line can't supply it you can't boost it up. Putting a large pipe on the end of a garden hose doesn't get you more water.
     
  12. dpeilow

    dpeilow Moderator

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    #12 dpeilow, Dec 30, 2008
    Last edited: Dec 31, 2008
    Just catching up on some old stuff here.


    Good god man, you've solved the World's energy problems!

    Why are all those silly scientists spending millions on nuclear fusion research when all they needed to do was give everyone some step-up transformers? And there's Tesla's engineers selfishly sitting on this development and not releasing it to the public in their cars...
     
  13. Joseph

    Joseph Member

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    just-an-illusion, please read everything I'm writing:

    Amps x volts = watts.

    Watts are a unit of power.

    Watt hours are a unit of energy.

    Energy (and thus power, because energy is power over any certain period of time) cannot be created or destroyed.

    Energy can only be converted. While in this conversion process, energy is lost, typically in the form of heat.

    Your idea of "stepping up the power" cannot be done. If you are plugged into a 110 volt outlet at 15 amps you are drawing (15 x 110) 1650 watts.
    A "step up converter" can step up either volts or amps, at the expense of the other.

    If you wish to step up voltage, amps would have to be sacraficed. So let's say you "stepped up" the power coming out of the outlet in favor of volts. Let's say this converter turned the 110 volts @ 15 amps into 220 volts @ 7.5 amps.

    If you multiply the two, you still get 1650 watts either way. There is no such thing as a converter that can put out more power than it takes in, because that would mean it is creating energy. And energy cannot be created or destroyed, only converted.'

    Now, if the energy coming out of a converter is exactly same total as coming in, why even bother "stepping up" the voltage or amperage. (But remember, that these are only stepped up at the expense of the other becuse the total energy has to be the same)

    Well, for some reason I don't know, a wire running with high amps and low volts is very inefficient. That's why the amperage is usually far lower than the voltage.

    But what if you want to be inefficient, and you want your wires to produce so much heat that they melt their plastic covering? This is very stupid of course, but if you really wanted to dot his then you would take your converter and make it take the 110volts @15amps and turn it into 15 volts @ 110 amps.

    It's the same energy, but for some reason high amps/low volts behaves very differently from low amps/high volts. High amps is very inefficient.

    Now, on the other hand, high voltage is very efficient. That's why the electricity running through high-power lines in your neighborhood is extremely high voltage and very, very low amperage.

    Now, in an electric car, why would you want to step up voltage? Well, as I've always been told, roughly, in an electric motor, the following happens: more voltage = higher rpm and more amperage = more torque.

    In an electric vehicle, the motors are more efficient at higher voltage (and thus at higher rpm) In many hybrid vehicles, there is a transformer that turns the energy coming out of the batteries into very high voltage. Why? Because higher voltage is more efficient.

    You should watch some videos on youtube about electricity. Just put in "electricity basics" and you'll get a bunch of informative videos. I watched these two videos a long time ago and I remember liking them.

    YouTube - Basic electricity 1/2 and
    YouTube - Basic electricity 2/2

    And here's a little extra info about something I'm not 100% sure about.

    (Voltage is the "pressure" between negative and positive. Amps is the rate at which electrons move. The following I'm not sure about: I think since amps is the movement of electrons, that means it creates more friction within the wire than voltage, so that's why amps is less efficient. Someone correct me if I'm wrong.)
     
  14. just-an-allusion

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    By way of refuting the apparently dismissive nature of your use of the analogy...
    ...to address my suggested technological advancement/perception of designer oversight, I am not going to belabor my point by recapping the technology behind the stepping UP circuitry of, e.g., microwave ovens (an inherently AC application), or that of automotive power inverters (inherently DC-AC applications), or even that of MOSFET circuitry for that matter (all of which amplify the incoming current, be it AC or DC, via "stepping up" or "resonance" modulation, to levels required to perform their respective tasks), but will only direct you to recall the very namesake of the object under contention (not to mention this very website), i.e., the "Tesla" Roadster, to address your comments: How Tesla Coils Work
    "Basic" physics be damned, this is the future, this is advanced physics...a majority of it ("basic physics" concepts) are wrong/misapplied anyway.
     
  15. just-an-allusion

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    #15 just-an-allusion, Dec 31, 2008
    Last edited: Dec 31, 2008
    Hmm, six(6) words:

    Low to high voltage converter circuitry....

    Just two(2) words for you:

    Tesla (sound familiar?) coil....
     
  16. just-an-allusion

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    Perhaps not quite yet, but I am working on it/doing my part...thank you for the encouragement though, it is appreciated. :smile:

    Because the military/government is funding the backing and fusion is way better than the conventional fission technology currently employed in our industry.

    I believe that everyone here knows the utter turmoil that Tesla has been undergoing for some time now...such matters can be quite distracting to the technical mind, plus, sometimes the hardest thing to see is that which is right before your nose.

    One could also pose a reasonably rationale argument that they're being suppressed by the Big Oil and automotive industry magnates, both of which stand to lose e-v-e-r-y-t-h-i-n-g that they've invested billions upon billions of dollars and decades worth of R&D into....
     
  17. doug

    doug Administrator / Head Moderator

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    #17 doug, Dec 31, 2008
    Last edited: Jan 1, 2009
    I don't want to say too much about this since there are plenty of reasonable resources online. What Joseph said is pretty much right and the things about which he's not sure, he seems to have a good intuition. I'll just add that the reason high current is inefficient is because a normal (non-superconducting) wire has some finite electrical resistance. And the power dissipated as heat in a wire goes as the square of the current times the real part of the impedance. P=R*I^2 (In general the impedance is complex (has both a real and imaginary part).)

    The garden hose analogy is actually quite a good one. The water pressure is like voltage and the flow is like current. Pushing the analogy a bit further, you can place your thumb partially over the end of the hose and get a lot more pressure, causing the water to come out at a higher velocity. But the total flow rate is reduced as a consequence.

    None of this stuff is by any means considered advanced physics. It's the kind of stuff that could be learned in a good high school physics class with just algebra. In a college physics course you'd use basic Maxwell's equations and it would help to know some vector calculus. But for this stuff you don't need to use any of the "advanced" topics like field theory, general relativity, or even quantum mechanics (unless you're considering the fundamental source of electrical resistance). (Special relativity is implicit in the Maxwell's equations.)
     
  18. malcolm

    malcolm Active Member

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    If you are delivering electrical energy at the rate of 100 W then you could choose to do this at 100 V x 1 Amp or 1 Volt x 100 Amps or any other combination you like.

    But if you increase one, the other will always reduce since (in this example) the limit is 100 W. You can't get more power out unless you put more power in. Ever.

    In fact you always get slightly less because any system which adjusts the balance between Voltage and Current will incur energy losses. For Transformers it's Eddy Current and Hysterysis losses. Other devices have other sources of inefficiency.

    Sidebar: I^2 x R is also known as "Joule Heating". Energy loss via this mechanism depends on current rather than voltage because current affects the drift velocity of the free electrons through wires - and hence the violence of their impact with atoms in the metal. Increasing the Voltage simply changes the packing density of free electrons.
     
  19. dpeilow

    dpeilow Moderator

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    Read that again and then tell us how you think the Tesla Coil steps up the power in such a circuit.
     
  20. WarpedOne

    WarpedOne Supreme Premier

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    True in average over longer time. However you can have steady 100W input and short bursts of say 1kW of output (for 1 second you get 1 kW and than for 9 seconds you have 0 kW output). But in average yes, you cannot get more out than you have put in. Period.

    Such a basic concept and people have so much trouble understanding it ...
     

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