3000 Farad 2.7 volt ultracapicator = how much "work"?

October 11, 2006 6:34 PM

How many watt hours, amp hours or "work" does this 3000 Farad 2.7 volt operating voltage ultracapacitor represent?

I think that I understand just enough to grasp that in measuring work-potential in electronics/electrics that most useful energy measurements in the realm are dependent on time/work or work/time.

Can anyone put the specs of that ultracapacitor into a measurement easily grasped by a layman?

(Tag refinement suggestions welcomed.)

posted by loquacious to technology (8 comments total)

A unit Farad is one columb of stored charge with a potential differnece of one volt across the capacitor's terminals.

A Columb is the amount of electric charge carried by 1 ampere flowing for one second.

So, 3000 F is 3000 A*s, or 0.83 amp-hours.
posted by b1tr0t at 6:42 PM on October 11, 2006

Close. You've determined how much charge is in the capacitor when it's at 2.7 V. You need a voltage term to get the energy, and since voltage is a function of charge you get into calculus.

Anyway the energy in the capacitor should be be 1/2 * C * V^2
This site explains the formula.

Assuming a fully-charged state of 2.7 V, I get 10.9 kJ (somebody check the math, please!) That's the energy consumed by a toaster/hair dryer in about 11 seconds, or a 60W light bulb in 3 minutes.
posted by Opposite George at 7:02 PM on October 11, 2006

Oh, and that's about 3 Watt-hours.
posted by Opposite George at 7:04 PM on October 11, 2006

Energy is the capacity to due work - in this case energy could be measured in Joules or Watt-hours (1 Wh = 3600 J = 3.6 kJ). According to the datasheet, that capacitor has a maximum energy density of 5.52 Watt-hours per kilogram and it has a mass of 0.55 kilograms. So it has a storage capacity (energy) of 3.04 Watt-hours (5.52 Wh/kg * 0.55 kg). For comparison purposes, a single alkaline AA battery stores a total energy of approximately 3 Watt-hours - just about the same as your ultracapacitor. No so great. However, what distinguishes an ultracapacitor from a rechargeable battery is its enormous instantaneous power. Your ultracapacitor's maximum power rating is 13800 W/kg, or 7590 Watts given its mass of 0.55 kg. Just the thing to power your gauss gun.
posted by RichardP at 7:04 PM on October 11, 2006

Some übercapacitor technologies don't have very high power density (too much internal resistance), but can still be superior to rechargeable batteries in some cases. The underlying principle of a capacitor is very different from a chemical battery.
posted by hattifattener at 7:50 PM on October 11, 2006

I've been using these things (actually, a smaller unit at 58F, 15V) for about a year.

They present some unusual problems.

For one thing, they are a dead short when empty, and you had better use some B.F. wires or deal with asymmetrical charge/discharge profiles.

They also have arc welder discharge currents. 15V/.0003 Ohms = 50 KA, declining of course, as discharge proceeds.

They last a long time, have good self-discharge characteristics, have great thermal performance, and make an excellent surge reservoir for pulsed applications. Maxwell sells them in modules for very large KW UPS of miniscule duration. Neatest technology I have seen in a while.

What's really cool is that they are not foil/insulator structures... the innards look like shipping foam. Charge is stored inside micro-scale holes which present acres of area, apparently. Way cool.

$100-120 for 15V/ 58F.
posted by FauxScot at 8:39 PM on October 11, 2006

One thing to keep in mind is that not all the energy inside the capacitor will be useful as the voltage will decline as the capacitor discharges. If you're running electronics, for example, you'll need a minimum voltage below which the remaining energy is unusable.
posted by TheOnlyCoolTim at 9:00 PM on October 11, 2006

Thanks for finding this and asking this question.

I've been thinking about trying to use a capacitor for a bike-light dynamo system in order to make the light constant for a wide range of speeds. I had no idea the technology had gotten as mature as these devices.
posted by jamjam at 10:04 AM on October 12, 2006