[geeks] Super/ultra capacitors for energy storage

[Bob]

 On 10/26/11, Jochen Kunz<jkunz at unixag-kl.fh-kl.de> wrote:On Tue, 25 Oct
2011 18:48:12 -0400
Phil Stracchino <alaric at metrocast.net> wrote:

[Supercaps]
> They also have insanely high charge/discharge *rates*.
Yes, but current LiIon / LiFePO4 batteries can be charged at 4C or 5C.
(I.e. you can do a full charge in 15 minutes.) Discharge rates are up
to 50C. I.e. a 5 Ah battery can supply a current of 250 A. Multiply
this by the typical voltage of the cell and you will get the amount of
power that is transfered during charge / discharge. It is not easy to
handle this amount of power. So even if the supercap can be charged /
discharged at a higer rate, the electronics behind it limites the rate.

Also keep in mind that most supercaps have a (sometimes very) high ESR.
So the charge / discharge rate is less then a normal capacitor.
--

Sometimes they add a resistor inside the capacitor to avoid welding or
blowing up the leads if there was an accidental short.  I have an old 3.3
farad,
5.5 V capacitor that has a 30 ohm internal resistor (it says so).  Good
for
demonstrating energy storage since it can keep an LED lit for a
surprisingly long amount of time.

Bob