Super capacitors

[ym2k]

Hi,

I came across some technologies on super capacitors. Here is an intro to it: **broken link removed**

I am pretty interested in it and wish to know how i can make use of it. Dunno if anyone of you have experience playing with this kind of capacitors. I will like to know, by formula, the charging time and which property determine the discharge time.

Thanks you.

 

[Nigel Goodwin]

Hi,

I came across some technologies on super capacitors. Here is an intro to it: **broken link removed**

I am pretty interested in it and wish to know how i can make use of it. Dunno if anyone of you have experience playing with this kind of capacitors. I will like to know, by formula, the charging time and which property determine the discharge time.

Thanks you.

They are usually used for very low current back-up purposes, cheaper VCR's used to use them.

 

[audioguru]

Hi Ym,
A capacitor charges from a resistor connected to a fixed voltage in a time called the time constant. It charges to 63% of the supply voltage in a time that is R times C seconds, where R is ohms and C is Farads.
The discharge voltage is the opposite, it discharges to 37% of its charged voltage by a parallel resistor in a time that is the same as above.

Some super capacitors have a very low current rating so be careful with the charge and discharge current amounts. Don't connect it to a voltage source or short it without a current-limiting resistor.

 

[ym2k]

So from what i see from your reply, it is basically just like a normal capacitor with high capatiance with low current rating?

 

[audioguru]

Unlike an electrolytic cap, a super cap has very low leakage current. The ones I've seen have a low voltage rating of 5.5V.

 

[ym2k]

Unlike an electrolytic cap, a super cap has very low leakage current. The ones I've seen have a low voltage rating of 5.5V.

So these is why it is so expensive? And it is not so commonly used?

 

[evandude]

my guess is they are expensive because they are made from different chemicals and processes from regular electrolytics... they aren't used a whole lot because there aren't that many applications that need such a large capacitance.... due to their low current handling capabilities, they are really only suited for backup purposes, and considering how cheap button-cell batteries are, they aren't always a good choice for that. However, they do have the one advantage that they can be charged many times, whereas most button cell batteries can't be charged at all, and the ones that can may be expensive, and not last through many recharge cycles.

I used to be involved in a field of robotics in which batteries were never used, only solar cells and capacitors... for that, the supercapacitors were very useful because they charged quickly but also stored a lot of energy. However, I worked at an electronics recycling place where we tore apart old electronics and sold the scrap, and only once in my entire time there (2 summers) did I find any supercapacitors in anything (they were in a gigantic old modem)

 

[audioguru]

Hi tech stuff is usually expensive until it is sold by the millions.
There aren't many applications for super-capacitors since flash memory IC's are so small and cheap. :lol:

 

[Oznog]

Some super capacitors have a very low current rating so be careful with the charge and discharge current amounts. Don't connect it to a voltage source or short it without a current-limiting resistor.

They often have a relatively high internal impedance too, some in the tens of ohms. This self-limits their discharge capabilities. But there are low impedance super caps, which are often used to compensate for high impedance batteries to allow them to supply high surge currents.

 

[Nigel Goodwin]

So these is why it is so expensive? And it is not so commonly used?

Basically because they are not much use for anything, low power memory backup in cheap equipment - and that's about it!. They also tend to have low reliability, it's a common failure in cheap VCR's.

 

[Reynard]

Hi all

i have a super capacitors (10F, 2.7V) and it is able to deliver high currents similar to batteries. It can operate a simple DC motor directly without any motor driver circuits. I have tried charging it with a constant power supply and of course through a resistor.

Does anyone know how to charge it using a sequence of pulses say amplitude of each pulse is 2V? These pulses are able to charge up a normal electrolyte capacitors about 4700uF relatively fast. But i still cant use them to charge up my super cap. I have heard about charge pump but how can i implement it to fulfill my goal??

Pls advise. Cheers

 

[Hero999]

Unlike an electrolytic cap, a super cap has very low leakage current. The ones I've seen have a low voltage rating of 5.5V.

That varys a lot depending on the application. Capacitors designed to improve the bass response in amplifier have a very low ESR and high leakage whilst those used as a memory backup have a high ESR and low leakage.

 

[Analog]

I have used super capacitors in regenerative braking applications. I have sitting on my desk a nice 5,000 Farad device.... Some people think that I mean 5,000 microfarads, and then are quick to correct me.... Then, of course, I have to correct THEM..