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Can You Power a Phone With a Capacitor?

wired.com

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Re: Can You Power a Phone With a Capacitor?

#21

Post by benjamincburns »

ISL wrote: post #15
benjamincburns wrote: post #9

Earlier quoted context omitted.

Most supercaps are rated for very low voltages (this one is only rated for 2.4V), as dictated by the breakdown voltages of the dielectric and its manufacturing tolerances. A 6V-rated 1200F supercap made from the same materials will be considerably larger. Further, most electrical engineers will enforce a factor of safety beyond the manufacturing tolerances . This is doubly true for capacitors, since dielectric failur…

High efficiency DC/DC converters are now commonplace. Energy density (J/m^3 and J/kg) and internal resistance are the really important quantities in energy storage capacitors.

Agreed. I discussed this elsewhere:

https://news.ycombinator.com/item?id=5799723

https://news.ycombinator.com/item?id=5799713

Re: Can You Power a Phone With a Capacitor?

#22

Post by leephillips »

benjamincburns wrote: post #18
vasco wrote: post #17

Earlier quoted context omitted.

At the cost of power which will increase your necessary total capacitance.

Digital circuits require some minimal voltage in order for their internal transistors to switch. This is because semiconductors only conduct in the presence of an electric field with a high enough potential to excite and free up the electrons hanging out near their junctions. That means that if your voltage drops below, say 1.8V (common for most low-power digital circuits these days), you won't be able to use your de…

I've learned something from your comments on this thread, and thanks for taking the time, but you've lost me with the barrels. Pressure depends on height of the water and is independent of the container shape.

Re: Can You Power a Phone With a Capacitor?

#23

Post by Elessar »

leephillips wrote: post #22
benjamincburns wrote: post #18

Earlier quoted context omitted.

Digital circuits require some minimal voltage in order for their internal transistors to switch. This is because semiconductors only conduct in the presence of an electric field with a high enough potential to excite and free up the electrons hanging out near their junctions. That means that if your voltage drops below, say 1.8V (common for most low-power digital circuits these days), you won't be able to use your de…

I've learned something from your comments on this thread, and thanks for taking the time, but you've lost me with the barrels. Pressure depends on height of the water and is independent of the container shape.

benjamincburns was referring to a barrel with a tap "somewhere near the bottom". The point being that it's very difficult to get stuff out near the flat bottom of the barrel, especially if you can't move the barrel itself. The other option with buck/boost converters is if the barrel's bottom tapers into your tap, so that there's no way for any liquid to avoid gravity's call and leave through the tap.

Re: Can You Power a Phone With a Capacitor?

#24

Post by benjamincburns »

leephillips wrote: post #22
benjamincburns wrote: post #18

Earlier quoted context omitted.

Digital circuits require some minimal voltage in order for their internal transistors to switch. This is because semiconductors only conduct in the presence of an electric field with a high enough potential to excite and free up the electrons hanging out near their junctions. That means that if your voltage drops below, say 1.8V (common for most low-power digital circuits these days), you won't be able to use your de…

I've learned something from your comments on this thread, and thanks for taking the time, but you've lost me with the barrels. Pressure depends on height of the water and is independent of the container shape.

Thanks for the compliment! As for the question, see what Elessar said.

Also:

In the typical water/electric circuit analogy the volume of water is synonymous to the amount of electrical energy stored (Joules). The pressure of the water is synonymous to the electric potential (Volts). Pipe diameter can be thought of as resistance (ohms), flow rate through a pipe (meters per second) can be thought of as current, and flow volume (cubic meters per second or litres per second) as power (watts).

Re: Can You Power a Phone With a Capacitor?

#26

Post by leephillips »

Elessar wrote: post #23
leephillips wrote: post #22

Earlier quoted context omitted.

I've learned something from your comments on this thread, and thanks for taking the time, but you've lost me with the barrels. Pressure depends on height of the water and is independent of the container shape.

benjamincburns was referring to a barrel with a tap "somewhere near the bottom". The point being that it's very difficult to get stuff out near the flat bottom of the barrel, especially if you can't move the barrel itself. The other option with buck/boost converters is if the barrel's bottom tapers into your tap, so that there's no way for any liquid to avoid gravity's call and leave through the tap.

That makes sense. I was over-thinking it.

Re: Can You Power a Phone With a Capacitor?

#27

Post by geuis »

finnh wrote: post #13
freehunter wrote: post #10

Earlier quoted context omitted.

Giga actually has an acceptable pronunciation with a soft g. The American National Bureau of Standards actually has this pronunciation formalized.

gigga what? gigga who? Switcha flow, getcha dough EDIT: apparently downvoters don't like Jay-Z.

You're being downvoted because your comment is inane, off topic, and adds nothing of value to the conversation. Even the grandparent quotation from Back to the Future suffers from the same problem and is being downvoted.

Re: Can You Power a Phone With a Capacitor?

#28

Post by crymer11 »

leephillips wrote: post #3

Amidst the general decline in quality of publications on the Web, it's great to see Wired , which put out lots of fluffy, inaccurate stuff in the past, publishing so many solid, interesting articles. This was fun to read, had actual equations and graphs, and made sense. I remember reading the headline about charging a phone in 20 seconds and not bothering to look at the details, because, no way.

Interesting, certainly. That said, I found this article frustrating to read because of the many spelling and grammatical errors; I don't want to start on stylistic issues. Does Wired not have a copy editor on staff?

For example, two that quickly caught my eye:

* "... just a plain boring capacitor." should have a comma between coordinate adjectives.

* "... the case were stuff is in the middle ..." should be "where" instead of "were".

Re: Can You Power a Phone With a Capacitor?

#29

Post by Dylan16807 »

benjamincburns wrote: post #16
zackbloom wrote: post #14

Earlier quoted context omitted.

You can use a DC/DC to boost the voltage.

Sure. In fact you'd want to use a high-efficiency buck/boost converter to take advantage of the entire discharge curve. However you're only storing about 20% of the energy at 2.7V. Edit: I'll show my work. Farads are Joules (energy) per Volt (electric potential) squared. That means that the formula for energy stored (E) in a capacitor is E=CV^2. A 1200F cap charged to 2.7V stores 8478 Joules of energy. A 1200F cap ch…

The point is that you don't need to round up. 2.7 volts is pretty close to 3, so you need pretty close to 2x2=4. Bump it to five to compensate for the rounding and look it matches the actual math. Half of your initial suggestion.

Re: Can You Power a Phone With a Capacitor?

#30

Post by pbo »

benjamincburns wrote: post #12

Here's her actual submission [1]. She created a novel dielectric and achieved an energy density of 20.1 Wh/kg which is about half of that of a lead-acid battery, and something like 6%-10% of a Lithium Polymer battery. She lists a capacitance per volume, but nothing about breakdown voltages, so I can't say what the size of her capacitor would theoretically be for 1200F rated at 6V. Nor can I say if it'd even be feasib…

It's useful when you have a circuit which needs a high-current burst which is powered from a low current (but high capacity) power source.

One application for this is lasers. I'm part of a team that works on a converter that uses wall power as an input to continuously charge a few dozens ultracaps then empties them all at once to fire very short pulses in the hundreds of kW.

What I find the most impressive about this is that the mechanical engineers have managed to fit this in a 2U rack.

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