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Supercapacitors, so they are not really super !

sram

Member
From my search in this forum, it seems like supercapacitros are just another type of capacitors. They differ from conventional ones by their ability to store more charge, but it is not like they will throw batteries out of the window. Nigel calls them useless and their name is stupid. What's weird though is the much literature that makes them something. I found many published articles talking about as if they are the super batteries of tomorrow or at least will be! How can such articles be published? Aren't they supposed to be peer reviewed?

What I can clearly identify as shortcomings of supercapacitors are their fast discharge rate (I mean it is not like I want to power a camera flash, but I want continuous power supply), and their lower energy density ( lower energy per unit weight compared to batteries) and that's a problem.

Or is it like there is hope with supercapacitors but it is too far-fetched ???

Sorry if this is a stupid question, but can you use a circuitry to use the charge stored in a supercapacitor in a better way? I mean modify the discharge rate?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
T = R x C

That's the equation - you can't alter it.

As I always say, their name is stupid (giving people a wildly exaggerated idea of what they are) - such as why you're even asking this question? :D

There are applications for them, but reliability has always been a big issue as well, with massive failure rates when they were used as memory backup in VCR's etc.

You can't alter the discharge formula, best you can do is a switch-mode up/down converter on the output to maintain a stable output voltage over a vastly improved range - but it's only enabling you to get more useful energy out of the capacitor, not increasing the amount stored.

For portable energy storage batteries are VASTLY superior.

Anything called 'super' or 'smart' (like smart TV's) is generally nothing of the kind, hence the name to try and con the gullible into believing it's something it isn't.
 

sram

Member
Self discharge is another apparent shortcoming. That's bad. So we have self discharge, fast discharge rate, and lower energy density. Can science overcome these?
 

sram

Member
T = R x C

That's the equation - you can't alter it.

As I always say, their name is stupid (giving people a wildly exaggerated idea of what they are) - such as why you're even asking this question? :D

There are applications for them, but reliability has always been a big issue as well, with massive failure rates when they were used as memory backup in VCR's etc.

You can't alter the discharge formula, best you can do is a switch-mode up/down converter on the output to maintain a stable output voltage over a vastly improved range - but it's only enabling you to get more useful energy out of the capacitor, not increasing the amount stored.

For portable energy storage batteries are VASTLY superior.

Anything called 'super' or 'smart' (like smart TV's) is generally nothing of the kind, hence the name to try and con the gullible into believing it's something it isn't.
So, even published scientific articles, you are not supposed to take for granted.
 

JimB

Super Moderator
Most Helpful Member
Way back in the 1960s (yes I am that old) I remember one of my classmates at college quoting his father saying that:

"A one Farad capacitor would be the size of Ireland"

So, yes a super capacitor is super in as much as it has a very high capacitance/volume ratio.
but,
it is still a capacitor, and behaves in exactly the same way as the 0.1uF caps that should be sprinkled around circuits to decouple the supplies lines.

A capacitor is a capacitor is a capacitor.
A battery is a battery (give or take the different chemistries).
They both store electrical charge, but the way in which they do it is completely different, hence their discharge characteristics are completely different.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Way back in the 1960s (yes I am that old) I remember one of my classmates at college quoting his father saying that:

"A one Farad capacitor would be the size of Ireland"
I think he was WAY out even in the 60's.

One of our instructors at college (in the 70's) worked on radar during WWII, and he used to say they used 1 Farad capacitors about the size of the classroom we were in.

Not a difficult calculation - look at the size of a 100uF - and see how much room 10,000 of them would take.

The 'clever' thing about super capacitors is their tiny size for their capacitance - but of course it's only very low voltage. I actually use them at work, as reservoir capacitors across batteries to power GSM modems (the lithium batteries used have much too high an internal resistance to provide the peak power required).
 

picbits

Well-Known Member
I used a couple on a project to start a car engine > 100,000 times once every 30 seconds or so. Everything was monitored and after a few months, we didn't notice any degredation of the capacitor. Handy if you want repeatability.
 

picbits

Well-Known Member
Off the top of my head they were 16v @ 500F each. There were two of them in parallel. Around £500 each if my memory serves me correctly but this was a couple of years ago.

It was impressive watching them pre-charge with my "little" 60A constant current supply then watching them start the engine and charge back to full within a couple of seconds when run on an alternator. We ended up disconnecting the alternator and using the PSU for the rest of the test for some reason unrelated to the capacitor.
 

schmitt trigger

Well-Known Member
The 1 F capacitor the size of Ireland should be correct if the dielectric is vacuum.

Of course, the purpose of all the modern capacitor dielectrics is to increase, quite dramatically, the volumetric efficiency. Even if it means compromise.
In this context, the “super” moniker makes sense in the fact that the dielectric is super effective in increasing the volumetric efficiency.

Of course, ALL the dielectrics have limitations and pitfalls, but any engineer worth its salt knows when and where to use them and avoid them.
 

nsaspook

Well-Known Member
Most Helpful Member
This can be seen as pedantic but it gets to the heart of the question.

A battery or a capacitor store electrical energy not charge. Both have the exact amount of existing charge when full or depleted of energy. The difference is the amount of charge separation. The problem with capacitor is not storage of charge, it's the physical process of moving existing charge to store electrical energy in an electric field. The physical electrochemical process (sub-surface chemical reactions) of charge separation in a battery is fundamentally more dense and end-to-end efficient than pure electrostatic surface charge energy storage.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
This can be seen as pedantic but it gets to the heart of the question.

A battery or a capacitor store electrical energy not charge.
Perhaps not?, considering the definition given us at college long ago was:

"Capacitance is the ability of a circuit to store charge in the form of an electro-static field"
 

nsaspook

Well-Known Member
Most Helpful Member
Perhaps not?, considering the definition given us at college long ago was:

"Capacitance is the ability of a circuit to store charge in the form of an electro-static field"
I could care less about what some college definition was years ago. The physics of capacitance is simple and fundamental to its energy storage density.
The energy stored on a capacitor can be expressed in terms of the work done by the battery. Voltage represents energy per unit charge, so the work to move a charge element dq from the negative plate to the positive plate is equal to V dq, where V is the voltage on the capacitor. The voltage V is proportional to the amount of charge which is already on the capacitor.
The total amount of charge in a capacitor or battery doesn't change, it's rearranged by a force as work.


Do capacitors store charge?
Capacitors do not store charge. Capacitors actually store an imbalance of charge. If one plate of a capacitor has 1 coulomb of charge stored on it, the other plate will have -1 coulomb, making the total charge (added up across both plates) zero. If you short circuit the capacitor by connecting the two plates with a wire of negligible resistance, you’ll see a sudden rush of current (depending on the size of the capacitor, this can result in sparks) as the electrons on the -1 coulomb plate rush onto the +1 coulomb plate. This sudden rush of current releases all the energy that’s stored in the capacitor.
 

nsaspook

Well-Known Member
Most Helpful Member

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