back to article Superfast-charging batteries? Whoa there, MIT

New battery technology developed at MIT has made a big media splash today, supposedly offering Li-ion energy storage which could charge up fully "in seconds". However, no such capability has been demonstrated: in fact the kit doesn't seem very important. The ink storm results from the usual advance notices attendant on a …


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  1. Dale

    In seconds

    My mobile already charges in seconds... 10800 of them.

  2. martin gorner

    too critical !

    I would definitely want a phone that takes just seconds to charge. You say fast charging battery technology is of mild interest for electronic gadgets. Are you out of your mind ? Imagine a laptop that could recharge during your coffee break. You then pick it up and return working in the park. Or did you ever realize your phone was almost dead just as you were leaving for that super-important meeting with a customer. Topping it up in 10 sec would definitely save the day.

    More generally, I dislike your calling scientists "boffins". Why use a derogatory terms for scientist? What is wrong with them? My opinion on the subject is that you were of the kind who would beat up bright kids in school because you had no other (intellectual) way of competing with them.

  3. Sarah Bee (Written by Reg staff)

    Re: too critical !

    In what universe is 'boffin' derogatory? It's colloquial. Some might even say it's affectionate. Derogatory is when I call you a wildly and erroneously judgemental little git. But then, some would argue that's just accurate.

  4. Anonymous Coward
    Anonymous Coward

    Tell me now

    How many kW do I need from the wall socket to charge any reasonable sized electric car battery in any reasonable number of minutes?

    I'm suspecting that the answer is a lot more than any reasonable domestic installation can supply.

    But that, as Lewis points out, probably isn't the point as far as the non-technical meejah are concerned.

    This might be interesting to those interested in battery-electric power tools and such, although the "two batteries, one on charge one in use" seems to work well for them already.

  5. Geoff May

    "Fast discharge is mildly interesting"?

    Mildly interesting?

    I think you'll find the BOFH will disagree there ...

  6. Neil

    Fast Discharging?

    My current mobile is great at that. One minute the battery is showing almost full, the next it won't even turn on. Nothing new here.

  7. D@v3


    who cares about a load of silly hacks and what they write?

  8. Anonymous Coward
    Anonymous Coward

    Special Wiring

    You mention that special wiring would be required to charge a phone at full tilt. Can you imaging the cable required to charge a 50KWh EV battery in seconds? More than that can you imagine the internal wiring to the battery pack?

    As for the capability to discharge in seconds can you imagine what would happen if you were to short the terminals on a 50KWh battery capable of discharging in seconds? The arc would certainly give you a nice tan.

    It all sounds nice in theory, but the devil is in the application.

  9. Tim Spence

    @ Sarah Bee

    Haha, brilliant - touché!

  10. Anonymous Coward

    limited value for average user

    The problems as I see them are:

    -You still would have to dump an enormous amount of energy into a battery to charge it this fast--far beyond the capacity of the electrical system in most households.

    -The waste heat generated by such fast charging must be incredible! And you thought Sony laptop batteries exploding was a problem!

  11. IR


    So how is it any better than ultracapacitors (which you mention, but no more)? They might not be widely available, but they charge and discharge very quickly. You don't want to stick them in your pocket with your keys though, unless you don't mind catching fire.

  12. Paul

    Quick charge == filling station?

    Those commenting about the wiring required at home for this sort of charging are surely barking up the wrong tree. How many people drive to their house, wait 2 minutes and then want to drive away again? How many people what to top up their fuel on the road when otherwise they would run out and don't want to wait 4 hours for the top up? Just because it could (possibly) charge quick does not mean it has to be quick charged in all situations and electric cars become much more usable if you can charge them up over a few hours at home but top them up in a few seconds when on the road.

  13. Anonymous Coward
    Anonymous Coward

    The maths

    I decided to look up how much energy a current electric car stores. An initial guess of 20kWh wasn't far wrong (for a reasonably sized, currently available, car)

    That 20kWh car does 100miles but I would say though that most people would probably want a car that could do about 400 miles on a "tank" (my car will do this on motorway miles quite easily) so we are talking more like 80kWh of storage.

    Lets "do the math" as our gas guzzling American friends would say...

    I'm going to assume that a recharge time of 10 minutes is acceptable. I'm giving it 10 minutes because I'm guessing if you timed how long you were at a petrol station for, what with queuing, filling, paying etc you don't get much change out of 10 minutes. So, if we could streamline the electric filling process e.g. automatic payments, no queuing you could probably get about 10 minutes of just charging.

    80kWh in 10 minutes equates to a supply capable of delivering 480kW. At 240V that is 2000A! There are calculations that can be done to tell you what wire size you need for a given load but the calculators I could find only go up to 400A which requires a cable with a CSA of 500mm^2. I would guess 2000A would require in the region of 2000mm^2. That would equate to a conductor with a diameter of 50mm - and you would need 3 of them.

    If we up the voltage to 7200V (local grid distribution voltage) then we need a more reasonable 67A. No online calculator will calculate will work with 7200V but at 240V a cable with a CSA of 25mm^2 will handle that load, that's still a pretty big cable though.

  14. blackworx

    BS Repellent

    My thoughts on reading that "story" in the paper today:

    Er, how do you supply enough current to do that even for a small battery? The charger will have to be massive. Wait a minute, why am I reading about this here and not on El Reg? This story is pish. Oh, wait a minute somebody somewhere's obviously looking for funding.

    Thank you El Reg for being always ready with the bullshit repellent... Of which I see there is now a special canister for us commentards. Ooh! Ooh! Do me! Do me!

  15. B Parnell
    Black Helicopters


    I am amazed that the MOD has not hushed this one up to use it for their new rail guns. Multiple MKVA discharging in seconds should really give them new guns a kick ;)

    Black Helicopter for obvious reasons!


  16. Anonymous Coward

    Boffins or not

    Two things - the issue about charging currents is important, but so is the issue of what happens when you charge. Does 100% of the electrical energy get neatly stored in the battery through a reversible chemical reaction, or does some of that get given off as heat? Answer - there's bound to be some heat - or actually, rather a lot. Same on rapid discharge - both charge and discharge will need current limiters to prevent overheating.

    @ Sarah bee re boffins - I'm with Martin Gorner on this one. Try this for a thought experiment - next time you're talking to a scientist for a story, try calling him/her a boffin directly and see how quickly your interview runs into the sand. 'Boffin' is really shorthand for 'scientist whose work is too complex to understand so I must demean him/her to feel less threatened by it'.

    As I say, call a scientist a boffin to their face and see if you get more than a weary smile back...

  17. John Smith Gold badge

    No big deal to you but Clarkson & Co think so

    Top Gear's dissing of EV's revolves heavily around the re-charge time. It is exactly about the time to "Top up."

    If you run out of charge suppose the AA of 2020 may have a charge cable to fit you, may not. It'll be faster to tow you to the nearest garage. But what can they do. Your Tesla still needs a long slow charge to get you home.

    Hence their fondness for the LH2 vehicle.

    Never mind its a deep cryogen (-253 C if you want it as low pressure liquid) or a high pressure supercritica fluid (5000PSI is well above critical pressure) and the mass on loaded would rate it as the equivalent of several Kg of TNT of stored energy (because work equals pressure x change in volume. USAF & NASA safety rules). This is before it ignites as a quite effective fuel/air explosive. And the hydrogen is still fossil fuel derived (from methane if your lucky).

    Re-fuelling it is however very convienient.

  18. James Pels

    Why melt your house?

    OK, so it could (maybe) charge in 9s if you were willing to melt your ring main, but...

    For ease of argument, let us say the battery has a 1Ah capacity. If it was to carge fully in 9s, it would need to take a charge at (60x60) / 9 = 400A. Most UK sockets are rated at 13A so this is clearly not going to happen in a normal domestic environment (and the internal losses would most likely be enormous if a suitable supply was found). However, charging at 13A would still only take approx 30 times longer = 270s = 4 to 5 minutes. I would happily pay a small premium for a phone that could realistically take a full charge in that time. Adding some reality though, expect it to take about two to three times that long to account for losses in the transformer - my HP laptop charger reckons it takes 1.5A @ 100-240V (~150 - 350W) and delivers 90W - oops.

    Here's desperately hoping these sums are right. If not, mine's the one with the broken logic and dodgy calculator in the pocket - you'll find it in the porch of that house that just caught fire...

  19. Anonymous Coward
    Black Helicopters

    Fast discharging

    Ahh at last the secret behind the US Army's EMP Grenade tech is revealed....

  20. Marky W

    @Michael Gorner @ The Lovely Sarah

    While part 2 of Michaels post was rightly (and deliciously) slapped down by Mistress Bee, his points of the first part are valid, if badly put.

    Just because the material can take 10 seconds to be fully charged in a lab with its sooper dooper power supply doesn't mean it should be charged at that rate in the home. My phone charger is rated at 240V / 130mA (say 30W ignoring the faintly-remembered phase-angle gubbins which may-or-may-not be relevant). A battery capable of taking 150W would mean it would charge in 18mins rather than the usual 90mins; a whopping improvement, and one which wouldn't result in wearing oven gloves to use it afterwards.

  21. Anonymous Coward
    Anonymous Coward

    How new?

    LiFePO4 batteries, a varient of Li-Ion have been around for a few years now (in commercial use) and offer greater safe charge and discharge rates (around 10 minutes) than standard LiIon. The penalty is that the total capacity of these is only 60-70% of the standard chemistry. Skim-reading the Nature mini-article linked, implies the new step is "The authors helped the ions by coating the surface of the cathode with a thin layer of lithium phosphate glass".

    I wonder whether this new super-fast varient still suffers the capacity penalty of existing LiFePO products or not.

    See also:

  22. Danny

    @Sarah Bee

    Thanks, I now have coffee all over my shirt.

    The mind boggles at the havoc one could cause with a rapid discharging 100Ah battery.

    Flames because.... well just imagine the pinch you could make with that!

  23. Anonymous Coward
    Anonymous Coward

    Why, Lewis ...

    ... I do believe you've been doing some reading!

    The whole recharging argument has been done to death in multiple fora, but just to recap one point: you can have a device installed in your garage that trickle charges overnight, at off-peak rates, at domestic 240V, and then delivers to the vehicle in a shorter time - maybe not 10 minutes, but a manageably short time. Not perfect though - I imagine it'll be a short, thick, black, flexible tube/cable thingy with some device on the end that you'll have to slot into a fitting on a your car - with a few sensible precautions, even - and then you'll probably have to watch a gauge thingy while it gets "filled up". Hmmm. Is it just me, or does that sound familiar?

    Oh, and by the way, I'm always amused by arguments that assume that EVs will be introduced and that *everything else* will stay the same. I'm sure when petrol cars first appeared, people argued, "But where will they get petrol from? There are nice, clean, safe water and feeding stations for horses, but petrol stations? And imagine if you tried to put that horribly dangerous petrol in a car by yourself? What if it caught fire and killed you? It'll never work! No, I'll stick to horse-and-cart, thank you."

  24. Anonymous Coward

    "Boffins" colloquial?

    Here I thought it was related to the verb, "to boff."

    So all these scientific breakthroughs AREN'T being accomplished by fellow Sodomites?

  25. Chris Miller

    @The maths

    Thanks and well done, that all looks very plausible.

    If you think about it though, a filling station where every vehicle takes 10 minutes to fill up would need to be able to service at least 8 (my village petrol station has 8 pumps) and for a larger establishment 20 (my local supermarket) recharging operations simultaneously. That takes us up to 10MW for every Tesco in the country.

    Put your money into wind turbines, folks (or, more likely, copper for all the new cabling that will be needed).

  26. richard
    Paris Hilton


    am i the first to ask how many people have had a fast discharge when they saw a paris hilton 'performance'?


  27. Paul McConkey

    @ AC 14:08 & Martin Gorner

    I'm with Sarah here - speaking as a scientist and with a scientist wife I can't say I find the term boffin at all derogatory. My 13 year old daughter doesn't even mind being identified as a boff in her top set maths class.

    Stop worrying so much.

    Mine's the lab coat.

  28. Paul McConkey

    @ AC 14:55

    "you can have a device installed in your garage that trickle charges overnight"

    A spare battery maybe? Just like my laptop, then.

  29. Anonymous Coward
    Anonymous Coward

    @Paul McConkey

    Sort of, but the device in your garage can be relatively bulky, ugly and cheap.

  30. Cameron Colley


    Strangely, I've always thought the term a little pejorative -- even though the research scientists I've met don't seem to take offence at the term. Perhaps it's like me being proud to be a nerdy geek?

  31. Peter Kay

    Solution - scalextrix!

    The solution is obvious - dig up the motorways, run a metal strip down the middle and adapt electric cars to use the high voltage track ;).

    One solution to the charging is to take more than ten minutes - if there's an attitude change that your car should be fully charged up (to 400 miles) before setting out, it would not be out of place to insist on half an hour's break after 400 miles..

  32. MnM

    @Tim Spence

    Kiss Ass!

  33. Clive Smith

    Charging basics

    People seem to think that batteries charge direcltly on 240 vac mains here! All charging is done via a suitable low DC voltage. The mains can supply 240vac @ 13A. If we convert that to 12V DC (not difficult) - we get around 260A.

  34. Sarah Bee (Written by Reg staff)

    Re: @Tim Spence

    Now now boys.

  35. Anonymous Coward
    Anonymous Coward

    Hold on...

    ..there seems to be some wild speculation regarding this tech and how quick it can charge. As I understand it these guys have developed a way to lubricate (so to speak) the ions passage through the cell so it can charge/discharge quicker (about 20X) and also staying cooler than current tech. Maybe more interesting to the industry is that it's not far from current their manufacturing process - apparently.

  36. ian

    Not economically feasable?

    There's no need for a 10MW mains supply for a "charging station". If you look around the back, you'll see a very large battery constantly on trickle-charge supplying 'leccy for the customers out front. This evens out the load seen by the mains, and averages it down.

    While it is a brilliant idea, I'll be modest about it.

  37. jake Silver badge

    @martin gorner

    "Or did you ever realize your phone was almost dead just as you were leaving for that super-important meeting with a customer."

    Uh ... when I'm about to meet an important customer, I turn my phone OFF! And I can't remember the last time I didn't have a spare, fully charged phone battery handy. Think ahead, man!

    Re "boffin" ... Last time I was labeled "senior member of the technical staff", my business cards read "Boffin At Large" ... It's not at all derogatory.

  38. Stevie


    "Spare battery and charger"????

    Since when?

    I tried to find someone who could sell me a desk charger for a spare phone battery for my Nokia a couple of years ago and couldn't find such a thing anywhere. I ended up using a Heath-Robinson affair from China which requires diddling about with sliding one-size fits all electrodes before securing the battery with what amounts to a plastic bulldog clip. I'm not at all sure the thing is even legal in my state.

    I haven't actually seen a desktop phone battery charger since the old analog days, come to think of it.

  39. Chris Miller

    @ian: "very large battery"

    You ain't kidding. My 'local supermarket' filling station is nearly always busy from 7am-7pm and opens 24 hrs. Let's suppose an average of 15 'filling up' during peak periods and 5 overnight. That means we 'only' need a supply that can average 5MW. But we would need a 'battery' that can hold 30MWh (or 110GJ if you prefer). That's about 50,000 standard lead-acid car batteries.

  40. Anomalous Cowherd Silver badge

    Rapid charge: It's not just for stations

    It's the regenerative braking. The amount of power required to slow a 1 tonne car from 30 to 0, even relatively slowly, is enormous. Without the ability to dump most of that back into a battery very quickly it's wasted. So a rapid charge battery is essential for EVs to work, and not just so you can charge at a filling station.

    Personally I really, really hope this works for charging as well.

  41. Anonymous Coward

    well, well

    my dictionary gives the relatively brief:

    bof·fin (bofÆin), n. Brit. Slang.

    a scientist or technical expert.

    [1940–45; orig. uncert.]

    Since I wasn't around back dinosaurs (oops, wrong article)...I can't say for sure either...but there is nothing there that would indicate pejorative usage.

    Sarah - where do I send to get my new keyboard? Surprised you didn't "ODFO" him... ^__^

  42. jake Silver badge


    I carry an ancient Nokia phone, a 5185 ... What I did was go to a thrift store and dig thru' the bucket of phones until I found a phone powered by the same battery. I found three identical to mine, and snapped 'em up at 50 cents each (the sales gal thought I was loony[she's right, but not for the reasons she suspected]). I already have the charge-cord. A side benefit is that now I have spare parts (this old thing is on it's third display). The funny thing is that even though I have a spare battery, I almost never use it ... The battery life on these old Nokias is awesome! The silly thing is over eight years old and hasn't lost a beat, at least not that I can see :-)

  43. Kanhef


    The main limit on the (dis)charge time of lithium iron phosphate (LFP) batteries is the rate at which lithium ions transfer between the cathode and electrolyte. It's essentially diffusion through a porous membrane, and the ions must approach the 'pores' within a narrow range of angles to pass through. This new coating 'funnels' ions through the pores, producing a dramatically higher transfer rate. I expect the improved efficiency will actually dissipate *less* heat, even at high (dis)charge rates. LFP batteries are much less prone to thermal runaway than the type of batteries used in most cell phones and laptops, so fire and explosion will not be significant risks.

  44. Andrew J Sutter

    Nature article DOES talk about charging -- though no data

    The Register says "In any case, Ceder and Kang - while apparently happy to speak to journalists of fast-charging, unless that was made up by the scribes - don't yet claim fast charging for their kit among their scientific peers." But the truth is more complicated than that.

    The title of the paper is "Battery materials for fast CHARGING and discharging" (emphasis added). And despite not presenting any charging data, the authors state in the penultimate paragraph of the main text: "The ability to charge and discharge batteries in a matter of seconds rather than hours may make possible new technological applications and induce lifestyle changes. Such changes may first take place in the use of small devices, where the total amount of energy stored is small. Only 360Wis required to charge a 1Wh cell phone battery in 10 s (at a 360C charging rate). On the other hand, the rate at which very large batteries such as those planned for plug-in hybrid electric vehicles can be charged is likely to be limited by the available power...."

    So the authors, not the "scribes", are generating the hype. So too Nature, which allowed this seemingly irrelevant text to stand.

  45. Anonymous Coward
    Anonymous Coward

    Overnight charging

    If you're going to charge up large batteries over night, you're going to need to install new very high current wiring. You could use a domestic installation, like that use for an electric cooker rated at 30Amps, 6 hours, = 180Ah. That's not going to be enough.

    Now, if a lot of people are doing this, charging up their car's batteries over night, think of the demand this is going to place on the electrical cabling from the transformer at the end of the street to the homes. I wouldn't be surprised if the underground cabling needs to be all ripped up, bigger trenches dug, and thicker cables installed, the existing transformers ripped out and new larger ones installed to handle the increased peak current demand during the hours of the night!

    This isn't as simple or trivial as people think.

  46. Jerry
    Thumb Down

    but why the bashing of the scientists...

    From all the versions of the article I have read online (which i admit is not *all* articles, haha), I have not read one where the scientists who developed the fast discharging batteries claim that their batteries do, in fact, charge quickly. So, I guess "the scribes are lying about this, too." Anyhow, I think it is unfair to put down a fairly impressive bit of materials science (and the people involved with its development) just because the media can't get its facts straight (and yes, Nature went out for a bit of publicity). Yes, perhaps it isn't worth the media coverage it is getting, but don't make out the scientists to be committing some sort of fraud *without evidence* of their wrongdoing, that makes you no better than the rest of the media.

  47. Wize

    "you can have a device installed in your garage that trickle charges overnight"

    I don't have a garage, you insensitive clod.

    And many out there with a garage can't fit their car in.

    Not everyone can get their car near their house. Sometimes I'm lucky if I can park in the same street.

    And what if you drive to some holiday destination? Have to find a hotel half way there because you can't drive for more than 3 hours without a charge?

  48. BristolBachelor Gold badge

    Power isn't the only problem

    I designed some fast-charge, fast discharge Li-Ion batteries into a well-known brand's first cordless vacuum cleaner. It would have been possible to give it a 15 minute charger, however the cost of just the charger would have added about £400 to the price of a £100 cleaner!

    A similar project used the same batteries for a wheelchair. They specified a charger that could charge it in 30 minutes. The charger was the size of an under-counter fridge and cost several thousand.

    You would have to really need it to have e.g. a mobile phone where the phone part that is used 24/7 costs a fraction of the charger which is only used for 20seconds a week.

    Where I worked it was an honour to be known as a Boffin. The model makers were known as "Cardboard Cutters" and the designers were "Flower Arrangers".

  49. Richard Hebert

    quick charge

    the alternate to quick charging is quick swapping.

    get out the highway and get to the battery station .. bit like in a car wash you

    drive your car up to the track , vehicle is then took over the change pit.

    robot takes the complete battery pack and sends it to the charge station ,

    ( at which point we dont care about charge time/amps /wiring etc. )

    then while still rolling a second robot gets a charged pack and swaps it in

    the car We would need a standard battery pack size for all cars.

    There's ways to get a fresh charge

    An alternate is a charge lane on the highway equipped with electrified

    tracks that you can connect to using a set of pads / rails .

    We will work it out, and get rid of the gun against our heads held by the

    OPEC and gas producing countries.

    They are running the economy of all countries to the ground by charging

    high gas prices. They know it. In fact as far as appearances go .. they count on it.

    Gas is our enemy , the gas industry is the enemy of the people.

    We need all the good ideas to set ourselves free from the slavery brought upon us

    by the use of gas.

    The coat : it's dang cold over here :)

  50. alan

    re AC 15:01

    Thats just disturbed me. I looked up "boff" in the urban dictionary. It has a whole new meaning for me

    At school we had the BoffMan. Boff's were little purple sweets and the Boffman was the icecream man who sold them.

    But now I am not so sure......

  51. chris

    Journos spouting off thru their rectum again

    Another case of Journos with no practical education misunderstanduing the brief and spouting off through their waste exits again.

  52. Chris Miller

    @Richard Hebert

    .. and if you swap the battery, then the exhausted battery still needs to be recharged. You can either do this on site or have a massive central recharging plant (probably sited next to a power station). In the latter case you've got to include the cost of transporting all these used batteries, so I guess you're no further forward. In either case, the resulting energy demands are unrealistic IMHO.

    Any 'green' transport system that wouldn't drastically curtail people's ability to travel has to address the problem of energy density. Batteries and capacitors are still a long way behind kerosene in this respect.

    Environmentalists need to either:

    a) invent a way of producing petroleum (or something very similar) in a sustainable fashion; or else

    b) figure out how to convince everyone that when they want to travel 100 miles to visit their mum, they'll need to book their trip with the authorities three months in advance (good luck with that).

  53. neil

    EV = Green?

    EV cars are green? No I don't think so, the resourse to build, run and dispose is far from green.

    Displaced pollution is the best they can claim.

  54. Mike Bronze badge

    change the batteries

    why does someone always suggest changing the batteries at the filling station? batteries have a fixed life, one day you get a decent battery and the charge lasts 300 miles, then you refill and 30 miles later you're flat because you got given the duff battery that the guy before you offloaded in to the filling station with a huge grin on his face?

  55. Andrew J Sutter

    re Jerry 02:34

    Jerry, I've read the Nature paper and you're right that the scientists don't claim fast charging. And I don't thnk anyone is accusing them of fraud. The accusation is *hype* -- and here the scientists are guilty. As mentioned in my 01:46 post, they not only mention charging in the title of the article, they include a paragraph about fast charging in their paper (including a mention of how it would "induce lifestyle changes"), despite the absence of any relevant data.

  56. Dominic Sweetman

    Battery charging at home

    A correspondent does the maths implicit in your article... Yes, charging my phone's 1Ah battery in 9 seconds would require a current of 400A. But that's only at 3.7V, so the amount of power involved is about 1.5kW, half of an electric kettle and well within the maximum of a regular 13A/240V plug. Surprisingly high currents are provided in domestic environments -- your PC power supply feeds its CPU chip with over 90A of current. Nine seconds: hardly. Three minutes? there's no obvious power supply reason why not.

  57. Anonymous Coward
    Anonymous Coward

    high currents at low voltages

    Dual core athlon X2 is 60 Amps, it's 89Watts at 1.5 volts. Your general value of 90 is too high.

    But in principle your argument is valid.

    Very high currents are achievable from the mains if the voltage is stepped down using a transformer.

    But providing chargers that achieve high current charging are going to by physically large, expensive and impractical and it's gonna weigh a ton. You're talking a massive transformer made of iron.

  58. Ken Hagan Gold badge
    IT Angle

    Boffins, nerds, geeks...

    ...fannies and bums. They are all offensive if the speaker intends them to be so and not if they don't. The same is probably true of most words. Have you never listened to politicians?

    IT angle:

  59. Jeffrey Nonken

    Low voltage, high current

    Those pointing out "It's only a few volts, convert the mains and you get lots of amperage" fail to note that carrying that high current requires some pretty big wiring. There are reasons we use high voltages for distributing electricity in the first place, and most have to do with efficiency. Otherwise, why not just run 30v directly from the generating stations? It would be a lot safer! But you couldn't get the same amount of energy through those skinny little wires.

    Think of pumping water: to move the same amount of water with less pressure you need a wider pipe.

    @Mike re: changing the batteries

    A good point that most people seem to miss. Or at least those who post, I rarely see it addressed. I'd say that to accomplish this fairly you'd have to rent the batteries instead of owning them, there would have to be an infrastructure of maintenance and monitoring. Probably chips in the batteries with serial identification and statistical data. I think it's quite possible to address, it just requires more planning than "all you have to do is have a way to swap the batteries out and charge them offline".

    I'm a firmware engineer. One of the scariest phrases engineers can hear (usually from management) is "All you have to do is". Occasionally it really is that simple, but it almost always means somebody has not thought through all the requirements and consequences (or can't begin to understand them) and has no idea what kind of resources it will actually take to implement. If you hear that phrase, grab your wallet and run screaming, because either you're about to launch into a bitter and time-consuming argument or you're going to get totally shafted on resources. Or both.

    So if you hear yourself saying (or typing) "All you have to do is" or anything that can be interpreted as "All you have to do is" then it's time to check your assumptions.

    In fact, check your assumptions at the door.

  60. MnM

    obvious reason

    Dom S, the power dissipated by a resistor (e.g. an electric cable) is given by the current squared * resistance. So while 1.5kW may be less than the average kettle, the kettle is happily sucking its juice from an appropriately rated mains cable at 240v, let's say at 8A. Using the same cable, at 400A, the heat dissipated by the cable would be 2500 times greater. You then need to start to care about heat, and this is irrespective of volts. Find a superconductor for the cabling and all this power loss goes away, but with current materials at these loads, power delivery becomes harder to do.

    That's why commentators above (e.g. AC near the top, shortly after some horrific brown-nosing) estimated necessary cable widths, suggested current limiters, etc. You mentioned cpus and power supplies: these both usually need fans. I couldn't confirm quickly, but think that power supplies deliver around 30amps in any one connection, and cpus step down the voltage locally.

  61. David
    Black Helicopters


    "What I did was go to a thrift store and dig thru' the bucket of phones until I found a phone powered by the same battery. I found three identical to mine, and snapped 'em up at 50 cents each"

    That kind of thing gets you locked up as a terrorist these days.

  62. Anonymous Coward
    Anonymous Coward

    @MnM stepping down voltage at CPUs

    CPUs step down the voltage locally? How do they do that when the the supply is DC?

    Are you suggesting that CPUs have DC-DC converters using switch mode or linear devices such as transformers on the chip?

  63. Tom

    I don't need a 10 second charge

    "This might be interesting to those interested in battery-electric power tools and such, although the "two batteries, one on charge one in use" seems to work well for them already."

    I have a light weight drill without the normal giant battery hanging off the bottom. The problem is that I can drain a battery much faster then charge one. If I could charge the battery in 15-20 minutes I would not have the problem of running out of juice before the second battery has a reasonable charge.

  64. Daniel

    It's an engineering problem

    "The power level involved would be similar to an oven: even if it somehow could be made to work without melting the phone, special domestic wiring would probably be required and the charger would be large and expensive."

    duh. You would likely only need to deliver about 10-20V DC. It is quite possible to make a charger that will do this at very high current, given that you have 240VAC at 13A available. Only heavy wiring would be charger output to the battery, which could be quite short - even 6 inches would do it. So voltage drop isn't such a problem as it might appear. Actually all you have to do is make sure the cable doesn't melt, the PSU can easily regulate away the voltage drop that occurs in the delivery wire by using a seperate sense wire back to the feedback network.

    The problem is quite a bit tougher for the size of battery that a car would need. But in Europe, many houses do have 3-phase coming in, so supply is not such a problem. Of course, the overall load on the grid would increase significantly ...

    I like the idea of switch in-out battery packs more, when you pull up at the filling station you just swap out a bunch of battery modules, pay, go. End of problem.

  65. MnM


    Beats me, which is saying little as I'm no expert. But PSUs put out 12, 5 and 3.3V, while cpus use around 1-1.5V (very approx), and I've seen references to transformers near the chipset.

  66. Anonymous Coward

    CPUs, hydrogen

    "CPUs step down the voltage locally".

    That's correct (ish), and without a transformer. Any worthwhile power supply these days (from phone chargers upwards) uses the miraculous technology of "switched mode power supplies", high efficiency, light weight, no transformer (maybe a small lightweight inductor with no metal or ferrite), marvellous stuff. Go read about it, this isn't the place for a lesson.


    Is not (just) a fossil fuel. In Iceland they make it from water and geothermal electricity. In Africa they could make it from water and solar electricity. As Europe (in particular the UK) is already buying liquefied natural gas from north Africa, we already have much of the technology to get liquid hydrogen from there too (they have no shortage of sunshine, and near the coast, water is freely available). Don't dismiss H2 so easily, you (or maybe your national electricity supply) may well need it one day.

    Not sure about LNG or LH fuelled cars in tunnels though - but don't tell the Highways Agency.

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