# CAP-XX Supercapacitors: 4.5V/cell for up to 100A in a CR123-like space!



## mailint (Sep 28, 2007)

I'm not expert in capacitors but I'm seeing that this company http://www.cap-xx.com/products/products.htm is already selling supercapacitors big like a single CR123 battery with comparable voltage that is able to discharge up to 100A in seconds, with a runtime of about 1/10 of it.

The question is: when we will see on the market flashlights powered by these little supercapacitors able to produce incredible amount of light for short times?


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## koala (Sep 28, 2007)

hmmm, you will need at least 10,080 farads to reach an AA cell at 1V capacity. http://electronics.howstuffworks.com/capacitor2.htm


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## mailint (Sep 29, 2007)

koala said:


> hmmm, you will need at least 10,080 farads to reach an AA cell at 1V capacity. http://electronics.howstuffworks.com/capacitor2.htm


 
Note that that article talk about normal capacitors. Here I'm talking about supercapacitors, with much higher capacities.

Here is why I believe that they can have 1/10 of the runtime of rechargeable batteries:

Type...............Energy Density (Wh/kg)
NiCd AA................41
NiMH AA...............51
Lithium ion.........100 

source: http://www.rcgroups.com/forums/showthread.php?t=130393

These supercapacitors have energy density of "1 to 5 Wh/kg".

source: http://www.cap-xx.com/resources/reviews/strge_cmprsn.htm (the final table)


Furthermore these supercapacitors can be recharged thousand of times within their lifetime of "30,000+ hrs average".


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## Fallingwater (Sep 29, 2007)

Even if they actually managed the very remarkable achievement of 100mah of energy at 4.5v in a supercap the size of a RCR123 cell, one has to consider that the voltage of capacitors goes down with the charge. Devices running on supercaps would probably need custom-designed voltage regulators.


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## mailint (Sep 29, 2007)

Fallingwater said:


> Even if they actually managed the very remarkable achievement of 100mah of energy at 4.5v in a supercap the size of a RCR123 cell, one has to consider that the voltage of capacitors goes down with the charge. Devices running on supercaps would probably need custom-designed voltage regulators.


 
I don't think that the voltage is a problem because they're selling them in dimensions as low as 28x17x1mm (http://www.cap-xx.com/products/products.htm), that is much below the size of an RCR123cell. This means that you can use many of these in serie to multiplicate the voltage.
Also consider that the "1 to 5 Wh/kg" energy density is calculated for a supercapacitor of "1 g to 2 g" of weight (http://www.cap-xx.com/resources/reviews/strge_cmprsn.htm)


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## slovensko (Sep 29, 2007)

http://en.wikipedia.org/wiki/Ultracapacitor

In 2006, United States Patent #7,033,406 issued for an electrical-energy-storage unit (EESU) using supercapacitors that can store 52kWh and weigh about 336lbs (152kg). That would give it an energy/weight value of about 342 Wh/kg, twice that of lithium-ion batteries.


At least we can look forward to this.


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## Fallingwater (Sep 29, 2007)

mailint said:


> I don't think that the voltage is a problem because they're selling them in dimensions as low as 28x17x1mm (http://www.cap-xx.com/products/products.htm), that is much below the size of an RCR123cell. This means that you can use many of these in serie to multiplicate the voltage.


No, this is not what I meant.
A LiIon's voltage goes from about 4.2 when it's full to about 3.something when it's empty.
A capacitor that is 4.5v when full will go to zero when it's empty, and what's worse it won't do so suddenly at the end of its charge like a NiMH cell.

Here's the discharge curve of a capacitor:







Taken from here - it says "It should be noted that the charge stored is not actually plotted - the voltage across the capacitor is plotted."

As you can see, the voltage varies widely. A device built to run on a capacitor and meant to deliver the same performance over time (such as a flahslight) requires a voltage regulator built to spec.
The good news is that capacitors have no problem delivering enormously high currents (relatively speaking), so the regulator should be able to get however many amps it needs to boost the output voltage without the capacitor overheating and its voltage decreasing as a result.
This will, of course, greatly shorten the running time, but the light should be able to run at full power for the whole of its charge.
The bad news is that we won't be able to just pop supercaps in place of CR123 cells in our existing lights without modding the electronics. That, and a tenth of the capacity of a CR123 (which means about 100, 150 mah) makes for a really really short battery life.


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## mailint (Sep 29, 2007)

Fallingwater said:


> No, this is not what I meant.
> A LiIon's voltage goes from about 4.2 when it's full to about 3.something when it's empty.


 
"3.something when it's empty" seems a contradiction to me. I believe that it must be 0v when it's empty, otherwise it won't be empty. The same for the supercapacitor.



Fallingwater said:


> A device built to run on a capacitor and meant to deliver the same performance over time (such as a flahslight) requires a voltage regulator built to spec.


 
I believe that a flashlight requires a current regulator, not a voltage regulator.



Fallingwater said:


> The bad news is that we won't be able to just pop supercaps in place of CR123 cells in our existing lights without modding the electronics.


 
Sure. I never thought to simply remove the battery and put a supercapacitor in my flashlight. Even the shape wouldn't fit 



Fallingwater said:


> That, and a tenth of the capacity of a CR123 (which means about 100, 150 mah) makes for a really really short battery life.


 
I would buy an emergency key-chain micro flashlight with 60 seconds of 1000 lumen light.


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## Fallingwater (Sep 29, 2007)

mailint said:


> "3.something when it's empty" seems a contradiction to me. I believe that it must be 0v when it's empty, otherwise it won't be empty. The same for the supercapacitor.


That is not true.
Or rather, while it is true that a LiIon still has a trickle of energy left when it's at three volts, it's also true that said energy is not useable. Getting a LiIon to zero volts is the second-quickest way to kill it (the first being overcharging it severely).
To all intents and purposes a LiIon is therefore to be considered empty when it gets to three volts, and should not be discharged further or damage will occur.

Capacitors, on the other hand, don't care about being discharged completely.



> I believe that a flashlight requires a current regulator, not a voltage regulator


LED flashlights often need more volts to run their emitters than can be provided by a single cell. Or they need less (think of lights powered by two CR123s). A voltage regulator is therefore needed.
A simple current-limiting resistor can be used if the light has a power source of close enough voltage to what is needed for the emitters.
In the case of the capacitor a resistor would not work, as the fully-charged voltage of 4.5 would drop quickly, and it'd soon be too low to fire the emitters. What would be needed would be a buck-boost voltage converter that would lower the voltage when the cap was full and boost it as it went under a certain level during discharge.



> I would buy an emergency key-chain micro flashlight with 60 seconds of 1000 lumen light.


What use is a light that only lasts one minute?
The only purpose I can see for it would be to attract the attention of potential rescuers in an emergency, but the ridiculous runtime would make it poor for that purpose. What if whoever is in the general direction of your beam of light is turned the other way and turns back just after your capacitor dies?

If you foresee finding yourself in an emergency, a small hand-launched rocket flare is a much more effective way of attracting the attention of potential rescuers.

If you don't foresee that then a hyperbright light with an extremely short run time would be useless. During an emergency it's much better to have an ordinary multilevel light (such as a compact Cree flashlight powered by a primary CR123 or two), which would be useful to find your way in the dark at low power but which would also work decently for attracting attention at full blast.

Here's an even better idea: want something that'll attract attention in the dark? Get a high-power (50+mw) green portable laser.
A flashlight is not easy to see inbetween foliage, trees and whatnot, and your rescuer needs to be looking roughly in its direction to spot it in the first place. And then it could easily be ignored ("must be a hunter").

A green, bright laser beam shooting up from the forest, moving and flashing the SOS code (which everybody ought to know) is sure to attract much more attention than a small flashlight, even if capacitor-powered and super-bright.


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## koala (Sep 30, 2007)

For Li-Ion, 0V doesn't only means empty, it also means it's screwed. Li-Ion with graphite negative electrode should not be discharged under 2.5V otherwise it will damage the cell. Some chargers cheap chargers refuse to charge cells under 2.5V.

Capacitors are voltage based devices, that is why they are also voltage rated. The voltage drops while a capacitor discharges. That's why they are important in timing circuits. Although supercaps are not designed for such application they are still capacitors.

Most hand wounded crank lights, has supercaps in it. Usually two 5F 2.5V in serial(5.0V). How long does the 5mm LEDs stay lit when it's fully charged? Not extremely long but it can be recharged again and again. The only(currently) advantage that supercaps has is higher discharge output, lower ESR, and more life cycles.

Supercaps has been around for a long time. Lets hope that they make them even better.


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## Fallingwater (Sep 30, 2007)

koala said:


> Most hand wounded crank lights, has supercaps in it


I don't know about that. I have two hand-cranked lights; one has a 3s 80mah NiMH pack, the other a LIR2032 40mah LiIon button cell.
All other such lights I've seen have rechargeable batteries of one kind or the other.
The only ones I know that use capacitors are the "NightStar" ShakeLights and their clones, probably because the charging method is too irregular to reliably throw energy in a rechargeable battery.


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## mailint (Oct 2, 2007)

What about the combination *lithium battery + supercapacitor* in a flashlight?


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## Fallingwater (Oct 2, 2007)

It'd be feasible from a technical point of view, but... why? The main problem of flashlights is not to find cells juicy enough to power them, but to improve the efficiency of the emitters.
If you wanted to have a big fat array of emitters powered by a cell that didn't require a backpack to carry it around, the technology is already available.
Lithium polymer cells meant for RC use have long been able to deliver many times the current of LiIons. Battery life when discharged at high current is unimpressive, of course, but a small battery + capacitor combo wouldn't be different.

Until some major breakthrough in battery technology is made, or environmentalists finally get it in their thick skulls that radioactivity isn't necessarily screaming death on a stick and we get readily available pocket-sized atomic batteries, our electronics won't run much longer than they do now, and capacitors won't be of much help in this regard.

Their main purpose is to power devices that need higher pulses of current than can be provided by the batteries alone (say, camera flashes), not to be a primary source of energy.

Another good use for them would be to allow regenerative braking in electric or hybrid vehicles. As it is, only a tiny fraction of the power recovered during regenerative braking goes back in the batteries, because they can't be charged nearly quickly enough. Yes, this does mean that the trumpeted regenerative braking feature of the Prius is in reality nearly useless.
A supercap bank could be charged more than quickly enough, though, and finally make it useful. 

This can be done already, but the cap bank required would almost double the price of the car. Prices need to come down a lot before we have supercap-equipped cars that don't cost much, much more than what would be saved by the system during the lifetime of the vehicle.


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## DM51 (Oct 2, 2007)

Atomic batteries / betavoltaics are being talked about in a different thread running at the moment. I don't know enough about those ideas to say whether or not they are likely to become reality any time soon, but it all seems like a bit of a pipe-dream to me. 

Continuing slightly off-topic, I would think miniature fuel cells are much more promising - certainly for small/medium-size applications like laptops.


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## Ron Schroeder (Oct 3, 2007)

The best mass produced cr123 sized super cap has the usefull capacity of about 50mAh. Prototypes are up to about 150mAh.

A Rebel 100 can convert about 40% of the energy going in to photons.

A 123 sized super cap can now run a Nichia CS to a reasonable brightness for 1/2 to 1 hour. But it can be charged in a couple of seconds.

I built a night light that will run all night on 2 123 sized super caps. It will recharge about as quickly as I can plug it into and take it out of a cagarette lighter socket.


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## DM51 (Oct 3, 2007)

Ron, that is fascinating! Are these 123-size supercaps commercially available? Are other sizes made too? What is the maximum discharge rate?


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## koala (Oct 3, 2007)

1F http://solarbotics.com/electronic_components/capacitors/2/

Right at the end of the page. Wire two of them in series to get 5V. Not very huge size but good for experiment. While your at it, check out the solar kits that works with the super caps.

Or try these 70 Farads $10
http://www.mouser.com/search/Refine...644+4294744842+0&Ns=P_Capacitance|0||P_SField


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## Ron Schroeder (Oct 5, 2007)

digikey.com

Search for Nesscap.

10 amps for 5 seconds for the 50F ones that I have.

About .03 usable watt hours into my boost LED driver until it stops running.

They now have a 120F version in about the same size now.


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## CM (Oct 5, 2007)

Fallingwater said:


> ...Their main purpose is to power devices that need higher pulses of current than can be provided by the batteries alone (say, camera flashes), not to be a primary source of energy...



This is the part most people miss when they start talking about how great supercaps are. They are designed as a temporary repository of energy, a supplement to a primary storage system like rechargeable batteries, fuel cells etc. They have lots of advantages but the disadvantages must be weighed in against the advantages.


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## mailint (Oct 5, 2007)

CM said:


> This is the part most people miss when they start talking about how great supercaps are. They are designed as a temporary repository of energy, a supplement to a primary storage system like rechargeable batteries, fuel cells etc. They have lots of advantages but the disadvantages must be weighed in against the advantages.


 
This is not exact.
Capacitors are designed as temporary repositories of energy. "Supercapacitors are unique in that they are able to combine the energy storage properties of batteries with the power discharge characteristics of capacitors" (source: http://www.cap-xx.com/resources/reviews/advantage.htm)

"I built a night light that will run all night on 2 123 sized super caps" (source: message of Ron in this thread).


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## Fallingwater (Oct 5, 2007)

Right.
Using the Oldest Analogy Known to Humankind (the water one), one could compare a capacitor to a bucket and a battery to a hose.

You can gradually fill up the bucket with the hose in order to then dunk all the water out at once, or you can use the hose directly.

You can, of course, punch a hole in the bucket and let the water come out gradually, but there's little point in doing that when the hose can do it by itself.


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## DM51 (Oct 5, 2007)

LOL - nice analogy!


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## mailint (Oct 5, 2007)

Fallingwater said:


> You can, of course, punch a hole in the bucket and let the water come out gradually, but there's little point in doing that when the hose can do it by itself.


 
With the (super)bucket alone you can dunk all the water out at once or spill it slowly. With the hose alone you have only the second choice.


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## Fallingwater (Oct 7, 2007)

mailint said:


> With the (super)bucket alone you can dunk all the water out at once or spill it slowly. With the hose alone you have only the second choice.


True, but the hose is connected to a big honking tank 

And if you just need to water your plants, as you will if (getting out of the metaphor for a moment) you're running a flashlight, you have no need for a bucket.


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## DM51 (Oct 7, 2007)

LOL, if it's dark you'll need a flashlight to see the bucket and the hose. And the plants too. 

BTW wtf is a "honking tank?" lol


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## IMSabbel (Oct 7, 2007)

The farad labels are quite decieving, btw. 
Note, for example, here: http://www.mouser.com/search/Refine...644+4294744842+0&Ns=P_Capacitance|0||P_SField
(link from above):

The higher the capacity goes, the lower the maximum voltage. the 70F ones are quite big, and only have 2.1V max Voltage.

As the thing thats actually useful is the stored energy (which goes with u^2), this makes those high numbers a bit less stellar.

Compare 
that last ultracap :70F, 2.1V, Stored Energy: 154J (quite a bit, btw)
10440 Cell (A lot smaller): 500 mAh, 3.6V: 6500J (quite a lot more)
(only rough estimates, of course. I would charge the cap to the max voltage, and the LiOn cell would need very low discharge currents to yield that much)

The thing is that for Flashlight purposes, the high discharge currents are useless, because the circuit thats able to deal with those would kill the size-advantages.

Ultracaps are cool for stuff like CMOS-Batteries, holding charges, everywhere where a battery should just bridge a gap in power supply.


And btw: that patent #7,033,406 is about something COMPLETELY different.
Their approach is taking the sensible approach: Low capacities and HIGHT voltages (as P=.5*CU^2). So their individual "cells" (they have 1000s in parallel) are only about 10mF, and use a glass insulator to get a high breakthrough voltage (they run at 3.5 kV). Thats the most basic type of capacitor (over 100 years ago, people coated waterbottles outside and inside with foil and used that that way).
A nifty optimisation of an old concept, but has little to nothing to do with what nowadays goes under the name of "supercap".


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## Fallingwater (Oct 8, 2007)

DM51 said:


> BTW wtf is a "honking tank?" lol


"Big honking" means, roughly translated, "huge-***".


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## DM51 (Oct 8, 2007)

Lol I had no idea - I thought it might be a tank for drunks to be sick into.


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## LED_Thrift (Jul 2, 2008)

*Re: wedding dresses supplier*

Post above has been reported.


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## FrontRanger (Jul 3, 2008)

Fallingwater, you make a good point about the need for regulation when attempting to use a capacitor as type of power supply. You're right that the voltage varies widely as it discharges. But the curve below is not applicable to what we're talking about:



Fallingwater said:


> Here's the discharge curve of a capacitor:
> 
> 
> 
> ...


 
That's a plot of the voltage across a capacitance C that discharges through a resistance R, with an initial voltage of 1V. It's the well-known exponential V(t) = e^(-t/(RC)).

If you forced a capacitor to act as the "power supply" for a regulator for a light, the regulator would force the circuit to consume (approximately) constant power. Constant power dissipation means that the energy stored on the cap would decrease linearly with time, and that does not happen when discharging the cap with a resistor. Since the energy stored on a capacitor is E(t) = (1/2)*C*V(t)^2, and E(t) decreases linearly, the voltage decreases square-rootishly. With the same initial condition of 1V, and assuming that the cap is fully discharged at time T, the voltage is V(t) = sqrt(1-(Ct)/(2T)), which looks like this:






So the problem you mention is still present: That is, there will always be some portion of unusable stored energy because no practical regulator can accept a line voltage of zero. But the problem is nowhere near as bad as the decaying exponential curve would make it appear. The actual function is "concave down", like a rechargeable battery curve. It's not as sharp a cutoff, so it's not as good as say, NiMH, but it's not unusable for a constant-power application.

With that said, I have no plans to pursue using ultracapacitors for my lights in the foreseeable future.

By the way, good point (elsewhere in thread) about the regenerative braking application.


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## Ron Schroeder (Jul 7, 2008)

Maxwell makes a couple of larger ultracaps that are in sizes that are somewhat useful for flashlights. They are C and D size at 140F or 350F respectivly at 2.5V. That's still only a few hundred mAh but it's enough for a Rebel 100. You can get over 70% of the energy out of a supercap if you discharge it to about 1/2 of its rated voltage.

By the way, the Prius can recover over 50% of the braking energy if you don't try to stop too quickly.


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## IMSabbel (Jul 7, 2008)

350F at 2.5V...
thats just above 1kJ... or about 100mAh for the biggest one, if you drain them totally dry.
I wouldnt consider this "somewhat useful" for a cell that size and with tha voltage characteristic.


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## 2xTrinity (Jul 7, 2008)

> 350F at 2.5V...
> thats just above 1kJ... or about 100mAh for the biggest one, if you drain them totally dry.
> I wouldnt consider this "somewhat useful" for a cell that size and with tha voltage characteristic.


Agreed

I don't see how any supercapacitor is desirable in a flashlight, which doesn't require anything close to 100s amps, even for the most powerful hotwires.

There are Lithium Polymer and LiFeP04 cells that are also capable of discharging in effect unlimited power, but without the low energy density and variable voltage constraints of capacitors. 

The A123 26650 cells, or the Emoli 26700 drill pack cells for example can discharge several tens of amps, ALREADY overkill for any flashlight, or they can "flash charge" in a few minutes if that's really necessary as well. Yet they still manage to have an order of magnitude or two more capacity than comparably sized ultracapacitors.

In order for an ultracapacitor to have comparable energy density to a Lithium battery (eg, those large wikipedia figures for energy density), they must be charged to extremely high voltages which is utterly unsuited for cars or portable devices due to safety.


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## IMSabbel (Jul 8, 2008)

2xTrinity said:


> The A123 26650 cells, or the Emoli 26700 drill pack cells for example can discharge several tens of amps, ALREADY overkill for any flashlight, or they can "flash charge" in a few minutes if that's really necessary as well. Yet they still manage to have an order of magnitude or two more capacity than comparably sized ultracapacitors.



You dont even have to go that for... if you compare supercaps with batteries, dont compare time to fill up... but compare time to get an equal amount of energy into the light.

Even with NiMh batteries, you can charge 100mAh in a couple of minutes.


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## Ron Schroeder (Jul 9, 2008)

Yes, but you can charge a Super Cap in a couple of seconds, not minutes. A couple of second charge could give you an hour of 25+ lumen light. Not a replacement for batteries but it fits a niche.


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