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

[Fallingwater]

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.

 

[DM51]

LOL - nice analogy!

 

[mailint]

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.

 

[Fallingwater]

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.

 

[DM51]

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

 

[IMSabbel]

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".

 

[Fallingwater]

BTW wtf is a "honking tank?" lol

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

 

[DM51]

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

 

[LED_Thrift]

Re: wedding dresses supplier

Post above has been reported.

 

[FrontRanger]

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:

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."

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.

 

[Ron Schroeder]

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.

 

[IMSabbel]

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.

 

[2xTrinity]

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.

 

[IMSabbel]

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.

 

[Ron Schroeder]

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.