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 letter …

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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.

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@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).

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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.

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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?

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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.

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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.

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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.

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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: http://en.wikipedia.org/wiki/Postel%27s_law

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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.

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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.

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Black Helicopters

@jake

"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.

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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?

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Tom
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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.

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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.

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MnM

@Rota

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.

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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.

"Hydrogen"

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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