Energy From a Supercapacitor

[Renato_power_darkness]

Hi folks!!!


Is there a way to measure the max energy released from a capacitor ?..
For example. The max power released to a charge is the match impedance.. and how about the energy ??.


best regards ..

[T3sl4co1l]

Yes. Discharge it at a fairly slow rate, so that leakage and conduction losses are balanced (somewhere between minutes and days).  Dissipate the energy into a perfectly insulated calorimeter (a well enough insulated one may not exist though), or measure V and I or P and integrate over time.

The capacitance can be known quite accurately over the same time scale, and the charge is linear with voltage, so E = C Vmax^2 / 2 also applies.

Power transfer theorem doesn't apply here: that would yield 50% efficiency. We can do better.

Tim

[Renato_power_darkness]

Thank you so much, Tim.

There are lot of details in the test (fairly)  I'm gonna check this out.   

Best regards!

[HighVoltage]

I have done this in the past with a Keithley 2460 SMU, draining a Supercapacitor with a fixed current and use a script inside the instrument to calculate the total capacitance, energy and power. You can even graph it nicely with the 2460 SMU.

[Conrad Hoffman]

The energy is remarkably small, which is why energy storage as charge can't compete with things like batteries, save for short term high current loads.

[HighVoltage]

I worked a lot with Maxwell 3000F Super Capacitors up to 2.7V
It looks really amazing, when charging them with 100A and the voltage rises so slow.
Almost unbelievable.

This 3000F capacitor has an energy storage of 10,935 Joules at 2.7V
 

[guenthert]

[..]
This 3000F capacitor has an energy storage of 10,935 Joules at 2.7V

     So I need only about 12 of those to absorb the kinetic energy of a (1300kg) car coming to a stand-still from 50km/h?  That's quite impressive.

[T3sl4co1l]

Or to accelerate it to the same speed.  Better have a powerful inverter and motor. 

Tim

[Conrad Hoffman]

OK, so that cap is 60 mm in diameter and 138 mm long, and it has the energy storage of an AA lithium ion battery. Admittedly it can charge and discharge very rapidly, but in terms of energy storage it's not in first place.

[T3sl4co1l]

They don't find much use in EVs because once you have enough cells together, you have more than enough power capacity to do anything you want.  Same reason we're happy to use 1000s of uF of electrolytics instead of the bare minimum (100s uF?) ceramics in a switching supply: the power capacity is adequate and the price is right.

Tim

[HighVoltage]

One benefit for EVs would probably be the ultra low internal resistance of the super capacitors and therefore the fast charging from regeneration of breaking energy. So, like a buffer between the regeneration and the normal cells.

Tesla bought the Maxwell comapny, the manufacturer of these super capacitors.
Time will tell, how they will utilize this technology.

[Renato_power_darkness]

Hi, mate!

I have a 2.7 V and 5F Maxwell. (I have another like 50 F)

What I'm trying to find is a fair way to measure the maximum energy deliverd, with lossses and realistc contents.

Did you get 10 joules from the manual ??

See yah

[Renato_power_darkness]

I'm gonna try to get the discharve voltage curve under de charge, by an oscilocope and then, convert to power over time and then, integrate the area.


Thank you so much !!

[Ed inMelb]

UM, I make Super Caps and batteries, and I made a super cap as big as a shoe box that weighed a couple of kilo's.... INSTANT POWER!!

[David Hess]

If you know the capacitance, then available energy is simply 1/2cv^2, which means that when discharged to 1/2 of the starting voltage, 75% of the energy has been removed.