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Electric vehicles don't add up

  1. Dec 28, 2008 #1
    How do you get through to people with poor technical/scientific knowledge that battery vehicles have considerable snags particularly the long charging times??

    I keep being told that future cars will be charged in 5 minutes.
  2. jcsd
  3. Dec 28, 2008 #2


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    The best way to get others to accept your idea is to compose a proper argument which consists of a claim, support, and warrant. :smile:

  4. Dec 28, 2008 #3
    You can go through all the figures like needing a Megawatt elec supply and cables and plugs which can safely handle hundreds or even thousands od Amps and/or high voltages but you just get accused of being negative.

    You would think that folks think the elec comes from thin air.. It costs little, it is pollution free and it is 100% efficient. Sounds like they fall for manufacturers' hype. The press seem to fall for it as well.
  5. Dec 28, 2008 #4
    Huh? "people with poor technical/scientific knowledge" sounds condescending! I am sorry, but not every one in the world needs to be an engineer or a scientist..!

    there is always Google and Wiki and tonnes of simplified literature...so just point, I'd say (instead), "those who are curious", to some websites that explain why batteries need more time to charge etc., limited number charging cycles, battery safety etc.

    Reg what you are keep being told...is not necessarily incorrect!!

    The future cars need not be battery driven...Ultracapacitors are here - thousands of farads storing quite a bit of energy, at low voltage...compact, safe, rapid charging times, many charging cycles, getting better and cheaper day by day..!! Who knows, you could charge you car in 5 mins :D
  6. Dec 28, 2008 #5
    5 mins? Are you joking?
  7. Dec 28, 2008 #6


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    I suspect plugin EV only make sene to charge overnight on domestic cheap rate electricity.
    The limit on charging them quickly would probably be the batteries rather than the power cable, It might be possible to give a 5min boost charge to super caps but its not going to do lead acid much good.
    1000A cable wouldn't necessarily be thicker than a gasoline filler hose. 125A three phase is only about 3/4inch diameter and that includes all the extra layers of insulation for rough handling. DC is slightly different but if you are building a fixed installation like a gas pump you could put cooling into the cable. It might also make sense to use 400Hz AC as in aircraft and throw away some efficency in the rectifier but make transfromers smaller and lighter.

    Of course gas stations might be the wrong business model. PEV are going to be school run, city commute and shopping trips vehicles. Top up is likely to come as part of the parking fee. Malls would welcome it, if you are forced to spend an hour in their store rather than driving immediately to the competitor next door.
  8. Dec 28, 2008 #7
    Why not? Just because you and me dont know how this can be done
    does not mean it can't be done ....... :D.

    May be 5 mins is far out there, but is 20 mins ok for today? Say a bank of 1000 farad ultracaps charged independently....RC, with R = say 1 ohm , is 1000 seconds....
    This is not fiction, just google some stuff up...
  9. Dec 28, 2008 #8
    Why not.

    Whether is it batteries or capacitors or motors winding up springs you need a lot of energy. Energy is power x time. The shorter the time the more power you need.

    The tank on my car holds 150+ Kwh of useful energy after taking into account the efficiency of a petrol engine. If that was stored electrically you the best you could do on a British domestic supply would be 13 hours bearing in mind the losses in the charger and charging process. It would mean you couldn't have anything else on in the house.

    A 20 minute charge would require a 560 kW supply.. 250 Volts at 2240 Amps DC.

    A 5 min charge would be nearly 9000 Amps at 250 V. ... 2.2 MW supply.

    Not impossible but not very practical industrially BUT the people I was arguing with think the future will allow a 5 min charge AT HOME.

    I have told them they could do it if they had a huge Diesel alternator..
    Last edited: Dec 28, 2008
  10. Dec 28, 2008 #9


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    A plugin electric vehicle isn't going to store anything like the energy of a gas tank - but that isn't the point, a PEV50k (ie a 50km range) needs only store about 10KWh.

    To charge this overnight at home on 220V only needs about 5Amps.
    It could charge in 1hour at a parking spot with 200V * 50amps (ie booster cable size wires)
    Charging it in 6mins would take 500A at 200v or 250A at 400v - fairly chunky cables but not impossible - assuming that the batteries could take it (!!!)
    This would be very heavy cable, it would probably be suspended from a gantry above the filling point with a power assisted winch wire to make it apparently weightless to the customer.

    Remember IEEE cable power ratings assume constant power,these would only be used for 5mins and can then cool before the next customer. In the southern US you would probably need to actively cool the cables, either with oil or thermo-elctrical coolers. One nice thing about power leads this big - they are good thermal conductors!
  11. Dec 28, 2008 #10
    Your figures seem to assume near 100% efficiency in the charger and the charging process and 50 miles is a bit optimistic on 10 kWh. G-wiz owners are not getting the promised 48 miles althought many wont admit it. They seem to be out and out EV fans and gloss over the snags.

    People were refering to the Tesla Roadster with its 53 Kwh pack and a 5 min home charge.

    WHY doesn't somebody do some proper range tests??

    Top Gear fiddled it but are convinced their calculated 55 mile range driving the Tesla flat out on a track is accurate. 53 Kwh and 185 kW motors suggests a 17 min running time.
  12. Dec 28, 2008 #11


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    I agree. It really doesn't help anyone when people say that a 5 minute charge time is possible when current technology says it's highly improbable. Though there are technological workarounds for this.

    It looks like you've done your math and answered your own question. Did you explain this to them?

    Your numbers look a bit funny though.
    According to my calculations, that much energy(187.5kwh from your 5 minute rate) would propel my friends electric Porsche 914 at 60 mph for over 15 hours with a range of 926 miles. My gas powered car will only go between 200 & 300 miles per tank.

    But even cutting down your 9000 amps to 1/4 still yields 2250 amps. You'd need a nuclear power plant at every electric fillup station to pump that much energy that fast.

    The people I know that drive electric vehicles plug them in when they get to where they are going and unplug before they leave. If they want lots of range, they add a gas powered generator and operate in hybrid mode.

    What I'm curious about is why people are obsessed with electric vehicles having to meet every single convenience available in gas powered vehicles, and why they discount their market viability because of it.
  13. Dec 28, 2008 #12


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    50km, it was for VW's proposed EV.
    These are going to be european sub-compact size cars like a Smart/ VW lupo.

    I don't think 5min charges are going to be likely until we have super-caps.
    But one hour charge ups while parked at the mall are probably reasonable.
  14. Dec 28, 2008 #13

    I would like to know how you work that out.?? Sounds way out. I think I have seen figures of around 350 Wh needed per mile driving at moderate speeds which ties up with my car getting around 400 miles on a tank full (150 kWh - 187 is the power taken from the elec supply).

    The low weight G-Wiz crawls along and gets 30 miles (48 claimed??) or so with its 9,6 kWh pack. I think the max speed is only 40 mph.

    If you had a 150 kWh pack even with the best current battery technology the weight would be enormous ..maybe 1800 Kg on top of the weight of the vehicle.. It aint going to get much range at any sort of speed..
    Last edited: Dec 28, 2008
  15. Dec 28, 2008 #14


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    I believe I've posted the numbers before. They don't make much sense to me.

    It may be that his system is optimized for driving at 60 mph.

    The next time I see him, I'll discuss developing an electric-electric hybrid. :smile:
    Last edited by a moderator: Apr 24, 2017
  16. Dec 28, 2008 #15
    Last edited by a moderator: May 3, 2017
  17. Dec 28, 2008 #16


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  18. Dec 28, 2008 #17
    i believe i've read the suggestion elsewhere that a quick charge of supercapacitor-fueled vehicles would be done thusly: at your residence, you keep a stationary capacitor bank. this capacitor bank is charged slowly throughout the day or night, even taking advantage of off-peak power rates. when you get the vehicle home, you can then do a quick charge from one capacitor bank to the other.

    now, i ain't done the math, so i'm not sure what size conductor you'd need to keep the cables from fusing with a 5-min charge. the EEstor was around 3000V, so maybe not too big.
  19. Dec 28, 2008 #18
    We water cool cables carrying as much as 14K amps in resistance welding applications. The cables vary from 350 to 500 MCM.
  20. Dec 29, 2008 #19


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    This is similar to what I heard, except that the large caps, which would be more expensive, would be stored underground at fuel stations. At home, the car would be plugged in overnight, and take 6-10 hrs to charge. On the road, one could pull into a fueling station and charge up in 5-10 minutes, and a slightly higher cost than charging at home.

    Although I have met some people who think that EV's have no emissions, I have also met others who think that the emissions remain the same, and have merely been moved from the tailpipe to the smokestack. Both of these views display equally "poor technical/scientific knowledge." According to my math, if the only source of electricity in the whole world was coal burning power plants, the total emissions from an EV would be roughly one-half of what produced by an ICE.
  21. Dec 29, 2008 #20


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    Even if they did have the same overall efficiency, EVs would still be better for the local environment. It's a lot easier to deal with a single smoke stack at a power plant than 1000s of tailpipes at street level.
    It's like dropping litter out of the car window compared to putting it in a trash can and then landfill - same total amount of litter, but easier to deal with.
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