Supercapacitor
The supercapacitor, also known as ultracapacitor or double-layer capacitor, differs from a regular capacitor in that it has a very high capacitance. A capacitor stores energy by means of a static charge as opposed to an electrochemical reaction. Applying a voltage differential on the positive and negative plates charges the capacitor. This is similar to the buildup of electrical charge when walking on a carpet. Touching an object releases the energy through the finger.
We group capacitors into three family types and the most basic is the electrostatic capacitor, with a dry separator. This capacitor has a very low capacitance and is used to filter signals and tune radio frequencies. The size ranges from a few pico-farad (pf) to low microfarad (uF). The next member is the electrolytic capacitor, which is used for power filtering, buffering and coupling. Rated in microfarads (uF), this capacitor has several thousand times the storage capacity of the electrostatic capacitor and uses a moist separator. The third type is the supercapacitor, rated in farads, which is again thousands of times higher than the electrolytic capacitor. The supercapacitor is ideal for energy storage that undergoes frequent charge and discharge cycles at high current and short duration.
Faradis a unit of capacitance named after the English physicist Michael Faraday. One farad stores one coulomb of electrical charge when applying one volt. One microfaradis one million times smaller than a farad, and one pico-farad is again one million times smaller than the microfarad.
Engineers at General Electric first experimented with the electric double-layer capacitor, which led to the development of an early type of supercapacitor in 1957. There were no known commercial applications then. In 1966, Standard Oil rediscovered the effect of the double-layer capacitor by accident while working on experimental fuel cell designs. The company did not commercialize the invention but licensed it to NEC, which in 1978 marketed the technology as “supercapacitor” for computer memory backup. It was not until the 1990s that advances in materials and manufacturing methods led to improved performance and lower cost.
The modern supercapacitor is not a battery per se but crosses the boundary into battery technology by using special electrodes and electrolyte. Several types of electrodes have been tried and we focuse on the double-layer capacitor (DLC) concept. It is carbon-based, has an organic electrolyte that is easy to manufacture and is the most common system in use today.
All capacitors have voltage limits. While the electrostatic capacitor can be made to withstand high volts, the supercapacitor is confined to 2.5–2.7V. Voltages of 2.8V and higher are possible but they would reduce the service life. To achieve higher voltages, several supercapacitors are connected in series. This has disadvantages. Serial connection reduces the total capacitance, and strings of more than three capacitors require voltage balancing to prevent any cell from going into over-voltage. This is similar to the protection circuit in lithium-ion batteries.
The specific energy of the supercapacitor is low and ranges from 1 to 30Wh/kg. Although high compared to a regular capacitor, 30Wh/kg is one-fifth that of a consumer Li-ion battery. The discharge curve is another disadvantage. Whereas the electrochemical battery delivers a steady voltage in the usable power band, the voltage of the supercapacitor decreases on a linear scale from full to zero voltage. This reduces the usable power spectrum and much of the stored energy is left behind. Consider the following example.
Take a 6V power source that is allowed to discharge to 4.5V before the equipment cuts off. With the linear discharge, the supercapacitor reaches this voltage threshold within the first quarter of the cycle and the remaining three-quarters of the energy reserve become unusable. A DC-to-DC converter could utilize some of the residual energy, but this would add to the cost and introduce a 10 to 15 percent energy loss. A battery with a flat discharge curve, on the other hand, would deliver 90 to 95 percent of its energy reserve before reaching the voltage threshold. Table 1 compares the supercapacitor with a typical Li-ion.
|
Function |
Supercapacitor |
Lithium-ion (general) |
|
Charge time Cycle life Cell voltage Specific energy (Wh/kg) Specific power (W/kg) Cost per Wh Service life (in vehicle) Charge temperature Discharge temperature |
1–10 seconds 1 million or 30,000h 2.3 to 2.75V 5 (typical) Up to 10,000 $20 (typical) 10 to 15 years –40 to 65°C (–40 to 149°F) –40 to 65°C (–40 to 149°F) |
10–60 minutes 500 and higher 3.6 to 3.7V 100–200 1,000 to 3,000 $0.50-$1.00 (large system) 5 to 10 years 0 to 45°C (32°to 113°F) –20 to 60°C (–4 to 140°F) |
Table 1: Performance comparison between supercapacitor and Li-ion
Courtesy of Maxwell Technologies, Inc.
Rather than operating as a stand-alone energy storage device, supercapacitors work well as low-maintenance memory backup to bridge short power interruptions. Supercapacitors have also made critical inroads into electric powertrains. The virtue of ultra-rapid charging and delivery of high current on demand makes the supercapacitor an ideal candidate as a peak-load enhancer for hybrid vehicles, as well as fuel cell applications.
The charge time of a supercapacitor is about 10 seconds. The charge characteristic is similar to an electrochemical battery and the charge current is, to a large extent, limited by the charger. The initial charge can be made very fast, and the topping charge will take extra time. Provision must be made to limit the initial current inrush when charging an empty supercapacitor. The supercapacitor cannot go into overcharge and does not require full-charge detection; the current simply stops flowing when the capacitor is full.
The supercapacitor can be charged and discharged virtually an unlimited number of times. Unlike the electrochemical battery, which has a defined cycle life, there is little wear and tear by cycling a supercapacitor. Nor does age affect the device, as it would a battery. Under normal conditions, a supercapacitor fades from the original 100 percent capacity to 80 percent in 10 years. Applying higher voltages than specified shortens the life. The supercapacitor functions well at hot and cold temperatures.
The self-discharge of a supercapacitor is substantially higher than that of an electrostatic capacitor and somewhat higher than the electrochemical battery. The organic electrolyte contributes to this. The stored energy of a supercapacitor decreases from 100 to 50 percent in 30 to 40 days. A nickel-based battery self-discharges 10 to 15 percent per month. Li-ion discharges only five percent per month.
Supercapacitors are expensive in terms of cost per watt. Some design engineers argue that the money for the supercapacitor would better be spent on a larger battery. We need to realize that the supercapacitor and chemical battery are not in competition; rather they are different products serving unique applications.Table 2 summarizes the advantages and limitations of the supercapacitor.
|
Advantages |
Virtually unlimited cycle life; can be cycled millions of time High specific power; low resistance enables high load currents Charges in seconds; no end-of-charge termination required Simple charging; draws only what it needs; not subject to overcharge Safe; forgiving if abused Excellent low-temperature charge and discharge performance |
|
Limitations |
Low specific energy; holds a fraction of a regular battery Linear discharge voltage prevents using the full energy spectrum High self-discharge; higher than most batteries Low cell voltage; requires serial connections with voltage balancing High cost per watt |
Table 2: Advantages and limitations of supercapacitors
Comments
I am highly impressed and interested in this topic, How I wish I have a full time research center I would have ventured into its advanced pioneering.
I am highly impressed and interested in this topic. I would like to know how does happen the charge and discharge in a double layer supercapacitor. What happen in the eloctrodes (reactions and ion moves) what is the role of the seperator and of the electrolyte.
I would like to know how an ultra capacitor helps or hurts an older battery.
Nice summary.
Maybe low voltage DC-DC conversion could be used to produce constant output voltage?
http://electronicdesign.com/article/power/ultra-low-voltage-dc-dc-converter-ics-a-br-font-cl.aspx
http://www.electrochem.org/meetings/scheduler/abstracts/214/0690.pdf
The second paragraph incorrectly uses mF to represent microfarards. This should be corrected to uF.
@spuzzdawg: Thanks very much, I have corrected that.
Fantastic. Is this an innovative idea? What are the application areas?
Joshua
Capacitors are used in various ways, with some of them designed for high-frequency circuits. Others are made specifically to handle larger amounts of voltage. Capacitors of various sizes and designs are used to tune radios, in clocks and electronic counting devices, in sensitive medical equipment and even in cars and electric vehicles.
Can Imuse a super capicity battery in place of a deep cycle 12 volt? and how isi it charged?
I would be interested in using ultracapacitors in an EV, in conjunction with my battery pack. I’m guessing I would wire them in series and in parallel with my battery pack. I have heard of a guy in Australia who has used ultra caps in his lead acid EV that has extended his battery life out to 10 years now. I want some of that!
Just wanted you to add that there are new generation of supercapacitors coming
www.tplinc.com
@Kevin
You might wanna check this out, perhaps this is what you think you heard:
http://www.csiro.au/science/Ultra-Battery.html
I doubt wether a DIY retrofit of super caps to a lead acid EV is feasible or safe. One would have to connect about 5 super cap “cells” in series over each lead acid battery if I’m not mistaken. Without some form of cell balancing and management, you’re heading for disaster.
Referring to the last paragraph: is possible perform a marriage between the batteries and supercapacitors in a harmonious way in order to increase battery life. Adopting a hybrid system. Consult the paper “Power and Life Extension of Battery-Ultracapacitor Hybrids” by R. A. Dougal, Senior Member, IEEE, Shengyi Liu, Member, IEEE, and Ralph E. White.
Excellent article but it leaves out the most interesting thing: the research which indicates that a supercapacitor in parallel with a lead acid battery greatly extends batterly life also increases its effective capacity (when used in electric vehicles). An unspoken downside to the current crop of Li-Ion powered 2 wheel vehicles (at least) is the short life and expensive replacement of the battery - perhaps ten times the cost per houir of the electricty used to charge it.
Is anyone in the United States working on combining Li-ion and supercapacitors? Is it possible to create a small/crude model for a lay person with some directions?
Does double-layer capacitor technology have a future in consumer electronics, possibly as a replacement for the antiquated Li-ion energy storage systems used in cell phone batteries?
Also, is “graphene” an example of DLC? I’m confused.
Any comments would be very much appreciated. Thanks.
I think we should remeber that supercapacitor development is more or less in the middle of it’s “curve”. I’ve no doubt we are yet to see many improvements, especially when one considers the ‘drive’ behind it. I mean CO2 pollution control and the need to reduce dependance on fossil fuels. (Supercapacitors can be charged by wind-turbines and nuclear power stations). Let’s not forget the huge political significance if our cars DON’T need petrol or diesel to propel them!
ho can i buy this one?????
Very interesting!
If any method using supercapacitors and batteries/dc-dc converters to replace the backup power supply system, please forward
I have patent pending technology that increases agm 12 volt output by 8-11% with no outside energy, I am wondering if this can be done with supers?
I am highly interested towards this topic and i am currently working on it , i require a very kind support from people around for its improvement basically in the field of its improvement on its disadvantages can the right direction be suggested by you ?
If you are going to connect a bank of supercapacitors across a 12v lead-acid battery for experimental purposes, you should observe the following:—
1) Each capacitor in the series chain cannot have more than 2.5 volts across it. Therefore some kind of balancing device such as zener diodes should be used across each capacitor in the chain. Remember a lead-acid 12v battery has 14.4 volts across it under charging from a typical car alternator.
2) You can’t just connect a supercapacitor across a battery as the battery will see it as a short in the 1st. few microseconds, or even a milisecond or two of charging the capacitor from the battery. This could blow up the leads, or set them on fire depending on how big the supercapacitor was. The circuit will need some resistive limiting until the supercapacitor has charged.
3) If you are wanting to save money in some way by using supercapacitors, forget it. A 1-farad 16volt supercapacitor will cost anything between £50 and £75, depending on sourcing. If you were thinking of 100 farads…..
4) A supercapacitor won’t store anywhere near the capacity of a lead-acid. But it will supply an instantaneous current far in excess of the battery, making volts-drop during cranking an engine to start it very much less, as an example.
5) A battery will supply a ‘fairly’ constant voltage during it’s discharge cycle; a supercapacitor won’t. It falls linearly with the discharge period. Therefore, some equipment won’t work after a certain voltage fall when there is still lots of energy in the supercapacitor. Sophisticated power-supply circuits are needed to use ALL the energy, or say, 90% of it from a supercapacitor; A dc-dc converter might be appropriate.
Hope this helps the students.
Fredllfixit.
I am connecting 132 capacitors(2.5V) in series with voltage balancing resistors. Please suggest one charging topology for this capacitor bank(350V) amomg boost converter and buck boost considering the minimum charging time slao. Pls help..
Voltage balancing resistors won’t do. They will discharge the capacitor soon after charge if they are of low enough resistance to work, and a high ohmic value of resistor will not ‘balance’ the voltage on each capacitor cell. Simple resistors are not voltage-sensitive.
You need as many zener diodes at 2.5volt working as there are capacitor cells. FYI, the zener has near infinite resistance with reverse voltage as usual with a diode*. But it won’t conduct until 2.5volts exist across it in the conducting direction, i.e. when you have deliberately chosen 2.5volt zeners. I could not begin to suggest a power rating for the zeners, but it’s going to be high, and expensive.
However, LEDs also ‘fire’ at 2.5volts, and if your supercapacitors are fairly small, there may be some possibilities here. However, don’t be surprized if a supercapacitor blows them up!
*Any semiconductor diode will eventually breakdown if you put enough voltage across it. This is the “avalanche-effect”.
Also, common silicon diodes have 0.7 volts-drop in the conducting direction. Four of these in series wont conduct until 2.4volts exists across them. These diodes are VERY cheap!
Fredllfixit.
If you rectify british mains into a reservoir capacitor, you get 330 to 350volt DC. Will that do?
Fredllfixit
Thanks Fredllfixit…i ve already made the capacitor bank..What i need is a good charging methodology without using micro controller..please help
I should think the only charging method will be to ensre it produces the design voltage, and has a series limiting resistor to prevent the charger from seeing the suparcapacitor as a ‘short’ for the first few seconds. The value of the resistor you should be able to calculate easily so as not to overload the current rating of the charger intiially
Fredllfixit..
Thanks Fred..The capacitor bank voltage here is 350V.So kindly suggest one charging method ..Like boost converter, Buck-boost etc…I wud be using one inductor for making this DC-DC converter..Hoew about charging the bank using a slightly higher voltage till it reaches the bank voltage..?
If you are building a charger from scratch to charge supercapacitors, prob. the best advice I could give would be to contact the capacitor manufacturers for their advice. Seems sensible after all, as they will have already done any specialized research in the matter. Usually these manufacturers are VERY co-operative with students using their own products. Liason with their people can often save a lot of time, and you will have ‘spin-off learning’ to boot. Making your own smart charger is hard work.
I would comment that I’m now wondering why such a high-voltage combo of 350volt? Are you propelling a car with it?
Fredllfixit.
thanks Fred..i ll try contact the manufacturer..
hehe I think Mahesh is designing energy storage for a solar power facility 
Trying to get some help. I am building a 72v vehicle with 24v in Super-Capacitor and 48v in AGM batteries. I f I provide a constant charge to the bank while the 72v motor is in use what would anyone recommend; do I have them wired in parallel or in series? What other device, diodes or equipment should I have installed in order avoid destroying any of the banks. The DC charge can supply a constant voltage of around 100v. Any assistance will be greatly appreciated. I am just a retired Navy Cryptologist, now trying to invent a homemade vehicle. Thank you in advance.
I’ve been playing about with the same thing… hehehe, blew quite a few this along the way.
I’m trying to use the supercapasitors to flash charge the car and allow it to trickle feed the batteries to keep/charge them up…
In turn filter some power off to run a small genie to keep the batteries topped up and with the help of small genies on the opposite side of the motors on each wheel hope to keep it going from 6-8 hours before a charge.
On batteries alone a BMW X5 big beast, lasts 2.5 hours. Hoping to get that to 6 hours… EASY EH hehehe…
Great to know others are playing about too…
I’ll post more if I achieve longer lasting power….
can you pls send me about the details about the super capacitor energy storage system mainly its capacity.your paper is very good.
i am trying to charge two supercapacitors (52F each) connected in parallel and aim to calculate its resistance and inductance. can anyone suggest me any charging methods and the calculations required to find the parameters?
I need supercapacitors to hold a chrge for a 15 hp dc motor 465 volts. I need to hold the charge for .5 seconds when the motor lost power.
I need .5 seconds pass through. Any ideas?
Thank you
Jim
Sir
I want to know how to calculate ESR value for 2.7 volt 25 F 6 no series ultra capacitor.
You seem to know a lot about capacitors , so my question is that I’m making a rail gun, and I need to know what will make it the strongest( it’s magnetic polarities) the volts or farad? If it is farad should I get 1 microfarad or 1 farad? I need it strong.
Once the Ultra capacitor is fully charged then how much time it will work without any external supply?
And if it is discharging in few seconds then how it can replace a battery while battery is discharging in2-3 hours??
And suppose i have to replace my vehicle’s battery with an ultra capacitor so how should i need to connect??
What is the circuitry to connect an ultra cap?
I have to make mobile battery charger.
If here we charge the capacitor with the help of dc generator then our input is zero but output get through charging.
I suspect that the best use of super caps in an electric vehicle is for regenerative braking. It takes a long time to charge a battery. It takes very little time to charge a cap. So when doing regenerative braking you need to get the electricity generated into something quickly. That means a super cap. Then let the cap charge the batteries. This uses the caps in a role they do best, a reservoir for charge.
good