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Comment by beat | Hacker News Reader

If something sounds too good to be true, it probably is.

Consider internal resistance, power measured in watt-hours, and thermal behavior. When I was a kid, I grew around drag racing. Lots of times, I saw incredibly powerful cars try to put over 1000hp to the wheels at once, and just snap an axle or explode a transmission.

An iPhone battery is about 5.45 watt-hours. To charge that in 30 seconds from mostly dead (say 5 watt-hours), you need over 500 watts, discounting any thermal losses! Do you think the tiny solder joints at the power coupling are really designed to take 500 watts of power? Devices designed for 500 watts of power look more like your refrigerator.

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Electronics moron here. What are the factors (or equations) involved in determining whether a certain type of joint/wire could take the required power for charging of this nature?

That is to ask, is it theoretically possible with high end materials to actually pull it off, or is there a physical size limit to using that power?

The most basic elements of electricity are volts (force) and ohms (resistance).

amps = volts / ohms watts = volts * amps watt-hours = watts * time

Bigger wire = less resistance, generally. So to increase amperage (and thus power), you need bigger wire. But resistance turns power into heat, so if you're trying to shove more power through, waste heat rises. Eventually, it can melt the solder joints that hold circuits together (solder is a very soft lead alloy with a low melting point). Meanwhile, too much power can easily fry the silicon of actual computer chips, and excess heat can cause other problems.

I'd argue that the most basic element of electricity is electrons :)

But rather than go down that road - an analogy that helps me understand amps is to think of it as bandwidth of water flowing through pipes. If you try to force too much water through the pipes too fast, they explode from pressure.

So, I guess, the answer is - there is no such material/metal/etc?

Resistance of a cable/wire is given by the formula R = <rho> * L / A where rho is the resistivity of the material, L = length, and A is the cross-sectional area.

It's a pretty straight forward formula. To lower the resistance, you either decrease the numerator (but a zero length wire is pretty useless) or increase the denominator (a huge-ass not even necessarily infinite, but just a conductor the cross-sectional area of say, the Pentagon, is technically possible but utterly pointless unless you're transmitting electricity cross-continent or whatever.

However, the resistivity of a conductor is its inherent property and so if there were a way to get a material whose resistivity was zero. Then you could transmit huge-ass amounts of energy over hair-strand thin wires because since <rho> is zero, you can play with other parameters in that formula without any fear. Hmm... (hint hint)

The material you need is: http://en.wikipedia.org/wiki/Room-temperature_superconductor

the search continues...

There are two important equations: Power = Volts * Amps Volts = Amps * Ohms Substituting these in you get Power (dissipated) = Current ^2 * R

This means for a given contact resistance, the energy dissipated as heat into that contact is proportional to the square of current. Note, however, that you can increase the power also by increasing voltage, and not needing lower resistance contacts. That is why laptop chargers are usually 19V, and power transmission lines are 500-750kV.

Typical toaster, coffee pot are ~800-1500 watts according to google. Pumping 500 watts into the phone might be possible as long as it is not via the normal usb connector. How long would that batter last might be different story.

https://www.google.com/search?q=toaster+wattage&client=ubunt...

1000 watts into a heater element is a very different thing from 1000 watts into delicate microcircuitry.

The only thing I can think of in the same league is a graphics card, the AMD R9 290X has a TDP of 250 watts I think, it's still quite a gulf.

And the 290X2 with 500W TDP, although that's technically going into two cards on the same board.

Yeah, I've only seen rumor quality information but I think that one might have an external radiator: http://videocardz.com/50102/amd-radeon-r9-295x2-pictured

This is probably what will happen...

http://www.youtube.com/watch?v=PqyUtQv1WoQ

two things that get very hot

500 watts represents 5-10 incandescent light bulbs, or 1/3 of a hair dryer. It doesn't seem crazy that if the power electronics of the battery and charger were designed right, that they could handle this.

Of course, the rate of change of temperature might be a little shocking - you can imagine that the battery case might heat up 20-30 degrees in the 30 seconds of charging. (~1 degree Celsius per second)

The tiny plug on my laptop seems to take 200 watts just fine. I doubt charging a battery as the article describes but you're going too far in the other direction.

That's because it uses higher voltage. See the comment above: https://news.ycombinator.com/item?id=7547420

Most of the pins of a CPU are actually power pins, because it can use >100W @~1V => 100 Amps through a lot of very small pins.

Higher voltage than what? The article doesn't list a voltage, it's far too non-technical for that. Even if you assume USB-like, modern specs put that up to 20 volts (with 3 amps on micro). But I'm sure this would have a heavier connector.

^ This. I'm wondering how this article, lacking substantial tech info, even made it here.

because on many sites an article like the above coming from WSJ is considered safe. Oh they get taken on occasion, but far less than sites whose only specialty is technology.

> If something sounds too good to be true, it probably is.

Too simplistic of a model.

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