Supercap D cells

[Brock]

Hummm, looks intresting...

http://www.electronicproducts.com/ShowPage.asp?SECTION=3700&PRIMID=&FileName=hlrr1.jun2004.html

What does 350F translate in to in mA, probably not that easy. Talk about fast charging though.

 

[Doug Owen]

A one Farad cap charges (or discharges) a volt per second at one amp.

This cap will provide one amp for 350 seconds loosing a volt.

Doug Owen

 

[PeterB]

Very interesting!
The energy stored in a capacitor is 1/2*C*U^2, this corresponds to about 0.2Ah (for 1.5V battery) => not very much for battery but could be usefull for very short running and ultra bright lights.

 

[gwbaltzell]

Plugged the numbers into Google™ with the following assumptions (and we all know about assuming): full charge to rated working volts 2.5, that we can discharge to 0.5 V, current drain a constant 500 ma (would not be true in real world!).

((350 Farad) * (2 Volts)) / (.5 ampere) = 23.3333333 minutes

Now of course we would be producing (2.5 Volts) * .500 amperes = 1.25 Watts at the start and
(0.5 Volts) * .500 amperes = 0.25 Watts at the end!

I tried to figure a constant power out but I think I strained my brain.


Could be fast to charge, just pick the max amps the connections can handle.

BTW - calculation is excactly the same formula as Doug Owen's

Would there actually be an interest in a light, which lets say, uses an underdriven 1 W Luxeon, provides light for maybe 15 minutes, but can be recharged in less than a minute? Of course we could use a larger model capacitor, but running these in series has issues.

 

[idleprocess]

How about using them to drive smaller arrays of 5mm or SMD LEDs? Maybe for flashlights or other lights that stick nearby to a larger power source for recharging - like on a boat, or RV. Mainly for applications where you're going to run them for a few hours at most and daily recharging isn't a problem.

I imagine that you'd want to keep the discharge profile somewhat low, since rapid discharges are rough on capacitors.

 

[idleprocess]

Same company has a 2600 F capacitor - albiet a tad larger than your typical D cell...

 

[gwbaltzell]

[ QUOTE ]
idleprocess said:
Same company has a 2600 F capacitor - albiet a tad larger than your typical D cell...

[/ QUOTE ]
Still not bad for a capacitor of this rating. Not quite 2 1/2 inches in diameter and less than 7 inches long.
Still trying to figure constant power and was reminded that 3/4 of the power is in the drop of half the original voltage. This helps by simplifing the lowest voltage we have to deal with.

 

[PeLu]

[ QUOTE ]
Brock said:
What does 350F translate in to in mA

[/ QUOTE ]

The capacity does not 'translate' into current, the more interesting parameter is the internal resistance. And this one is pretty low for these two mentioned capacitors (unlike with other high capacity ones).
Smaller ones could be used to drive a small flashlight at high power for a short period, lets say a 5W lamp for 10-20 seconds, so for example 3 or 4 AAA alkalines could be used. But I don't know if there is really a need.
When charging time is an issue, the 30-second rechargeables would be better...

 

[gwbaltzell]

It may be that where a capacitor based power source would shine (oops!) is in the number of times it could be charged in its lifetime. Also the simplicity of its charger which would only need to be voltage regulated and current limited unless super caps have a requirement I've not seen yet. The complexities of driving a LED are exactly the same as battery based as I see it. Because of a superfast charge time I seen no need to worry about having to change the capacitor for a charged one so access could be simplified. I hate to say eliminated since these do have a ten year life. I think there may be a real niche for a capacitor based flashlight beyond the toy shake light.

If I've plugged the numbers into the formula correctly assumming a starting voltage of 2.5 V and an ending of 0.8 V then the large 2600 F unit could provide 1.65 W for an hour. There may be an issue of keeping the power supply effective resistance low enough to fully discharge the capacitor to the 0.8 V.

 

[Brock]

What I am thinking you could use a single AAA battery and a step up to charge the super-cap. Then you could power a 5w from that. You could have a light that is small and runs a minute between self-charges.

Ok so it wouldn't really be practical, but it could be small and bright. Then again maybe not as small as a single 123 light anyway?

I am always looking for a light with a 10 min runtime and 250-lumen output about the size of an E2. Still waiting...

 

[gwbaltzell]

I'm confused! The capacitor is the size of a D cell. Why charge it from AA? Why not just use a D cell for the 5W? It would likely last about as long as a charge on the capacitor. Chart shows 1 hour at 1 A for a D cell. Might power a 5 W for 5-10 minutes? The 350 F capacitor could put out 6 W (edit: OK 5.8 W)for about 2 minutes (if my math is right). How many AAs would you have to use to charge the cap.? Sure you might be able to extract more of the energy out of them, but at a price of a long charge time. Plus conversion losses.

Edit: Got to thinking (always dangerous) that a rechargeable D or even F would probably perform well under a heavy drain. But I still think the 2 1/2 in. by 7 in. cap. would make a good flashlight under the right conditions.

 

[Brock]

True, and true. I am just thinking.

I guess the problem is we don't have a battery the size of a 123 that can put out 20w for 10 min without overheating. Oh well...

 

[Sub_Umbra]

[ QUOTE ]
gwbaltzell:
Would there actually be an interest in a light, which lets say, uses an underdriven 1 W Luxeon, provides light for maybe 15 minutes, but can be recharged in less than a minute?

[/ QUOTE ]

I've spent some time on big boats and ships and when I read the above question I immediately thought of a light that sits in a deeply recessed socket/charger built into the dashboard/control panel of any vessel large enough to be conned from inside. It would be used all the time. Most tasks requiring portable light in a pilot house are far shorter than 5 min duration. Drop it back into the dash, right next to the wheel, when you're done for an almost instant recharge. No charge memory, no voltage depression, hidiously high number charge/discharge cycles, and it would probably be easy to make it float(?) Highly theft resistant since it couldn't be recharged outside of it's dock. Auto-shutoff at three min and maybe a dim, slow blinking LED for that jerk who always forgets to put it back in its dock.

I think it would rock for many places where you need a few seconds of light very often. It might be good for a wide variety of control panels -- not just marine.

The trick would be to sell it to people who build control panels of all kinds.

 

[The Yeti]

I think that it would make more sense on installations which you DO NOT want to maintain. One example is solar cells put out a pre-defines maximum voltage. Add a few more volts onto it, you wouldn't have to worry about damaging the capacitor. For certain there is no worry about over amping the capacitor. These things have an 8 second minimum charge cycle.

One example is radio relay stations. The batteries for these installations often need to be changed via horse back.

Another example are illuminated road signs in remote locations, and emergency call boxes on freeways.

Around the home something you may appreciate is a solar powered night light where you don't need to change the batteries every 3 years.

 

[PeLu]

[ QUOTE ]
Brock said:
I guess the problem is we don't have a battery the size of a 123 that can put out 20w for 10 min without overheating.

[/ QUOTE ]

What about the organic radical cell (ok, only in development now) which could be charged in 30-seconds? I just assume that it should be possible to discharge it in about the same time....

And there are Li-Poli cells which they say could give up to 12C, the best NiXX high power cells (like the 3.3Ah SubC GP) give up to 15C.

Yeti: There should be many of these applications where you need lots of power only for a short time and you cannot use a thick cable. Like power tools.
When you have a switching power supply like in an Arc4 which can take an input voltage range of 1:3.5 you could use more than 90% of the capacitor's energy.

 

[idleprocess]

The power requirements of most handheld power tools are too high for this capacitor.

There are many battery-powered handtools whose utility is questionable due to the limitations of their batteries. Cordless circular saws and routers come to mind, since the current consumption of both when corded tends to be up to 15 amps. Every cordless circular saw I've seen uses a miniature blade (and usually is rated at an optimistic 50x 2x4 cuts per charge). I've only seen one cordless router - ever.

Ever seen the battery on the average cordless drill (and not those worthless power screwdrivers)? Odds are it's at least 12V (I've seen 36V drills), and weighs well over a pound. If I had to guess at the amp-hour ratings, I'd say they're north of 5 A-H.

 

[PeLu]

[ QUOTE ]
idleprocess said:
The power requirements of most handheld power tools are too high for this capacitor.

[/ QUOTE ]

The larger capacitor can deliver 600A at 2.5V, this are 1.5 KW and more than enought for most if not all cordless tools. Further there will be more than one cap used. Capacity will be another question.

[ QUOTE ]
There are many battery-powered handtools whose utility is questionable due to the limitations of their batteries.

[/ QUOTE ]
absolutely.

[ QUOTE ]
Odds are it's at least 12V (I've seen 36V drills), and weighs well over a pound. If I had to guess at the amp-hour ratings, I'd say they're north of 5 A-H.

[/ QUOTE ]
I don't know about any drill using a 36V power pack, but there is a Hilti rotary hammer (OK, it may be misused as drill .-). And they all use SubC cells, with very few exceptions. Usually 2Ah and 3Ah cells.

I know many craftsmen who use cordless tools pretty clse to the next power outlet, just for convenience. If the tool would recharge fast, they will be happy with pretty low capacities. Further I expect that the supercap has about the same capacity even for the highest currents (only higher voltage drop at the internal resistance).

(a little bit off topic: I use cordless rotary hammers a lot and I'm just making one with a Li Poli battery).

 

[idleprocess]

from Doug Owen:
[ QUOTE ]
A one Farad cap charges (or discharges) a volt per second at one amp.

This cap will provide one amp for 350 seconds losing a volt.

[/ QUOTE ]

For the D-cell foorm-factor:
350 F (assume 1 amp continuous current for amp-hours) / 60^2 = .0972 hours. Round up for convenience and we get a very optomistic 100 mAH (250 milliwatt-hours) - less than that in the real world due to voltage drop, etc. There is probably more energy in a mid-end watch battery than this cap can contain.

The largest supercap:
2600 / 60^2 = optomistic 722 mAH (1.81 watt-hours).

A garden-variety 2200 mAH rechargable AA battery represents 2.6 watt-hours - a somewhat more realistic figure than my simple calculations on the caps.

If you have to recharge your power-hungry cordless tool every few operations, why bother with making it cordless?

I can see this cap supplementing low duty-cycle battery-powered appliances for short, instantaneous power boosts and as the primary power source for low-power devices. The energy density is too low to act as the primary power source for a device that does any signifigant amount of work.

Perhaps in a few more years capacitor manufacturers will get supercap density high enough to displace betteries.

Look at brands like Milwaukee, Porter-Cable, and DeWalt for the high-voltage cordless power tools. I've seen 24V systems on store shelves, and seen 32 or 36V systems at trade shows. I'd imagine that higher voltages allow them to increase battery life by increasing current efficiency.

 

[gwbaltzell]

Drawn down by 1 V the 350 f gives and average of 2 W for 350 s or 700 joules. 700/3600 = 194 mWh
The 2600 f would be 5200 joules. 5200/3600 = 1444 mWh

If we can draw down another 1/4 V then we have 3/4 of the energy that was stored. And deliver 2.344 W over the same time frame.
350 f = 820 joules = 228 mWh
2600 f = 6094 joules = 1693 mWh

Divide by the midpoint voltage of your favorite battery chemistry to get mAh
Alkaline = 1.2 V
Lithium Manganese Dioxide = 2.5 V
NiMh = 1.15 V

Of course these are rated for 500,000 charges! How many batteries is that?

 

[INRETECH]

Batteries and SuperCaps, both have their places - the Storage Cap of a battery/Lb is much higher than a SuperCap, but due to its makeup of changing its chemistry during charge/discharge cycles, its limited - whereas a SuperCap is a cap and has no chemical reactions during its lifetime

My SuperCap:

http://www.inretech.com/pictures/cap4000f.gif