The Forever Rechargeable VARIABLE Super Capacitor Battery !!!

Introduction: The Forever Rechargeable VARIABLE Super Capacitor Battery !!!

About: Hi there! My name is Patrick, and I am an electronics engineering technician who works full time as a lab tech, and part time as an electronics engineer/salesman. I own an ebay store, and two websites, which …
Hi there!

What's all the Hubbub, bub?
This circuit acts as a never-dying, forever rechargeable battery.  If treated properly and with respect, it will live longer than you do! That's right! You will die before this variable battery does!  Eerie, eh?  The circuit employs about $90 worth of circuitry, but it sure beats buying batteries.  I use this circuit every single day when I get home from work to listen to music.  Depending on your input charging method (DC, solar, etc), charging can take only minutes.  With this, I can listen to music out of my computer speakers at high volume for about two hours before having to re-charge.   Use it to charge your cell phone. Use it to power your radio!  Use it as a portable power supply!  Wire it up to a flash light, or use it to power your halloween costume!  The possiblities are endless!  I am selling this in kit form!  See the last page of this instructable for details.

Need 3v?  You got it!
Need 9v? You got it!!
Need 12V?  You got it!!!
Need 34V???  You got it!!!!

The circuit uses SUPER CAPACITORS, as opposed to batteries. Super capacitors are like other capacitors, only they have enormous power storage capabilities.  Capacitors have two storage variables: Maximum charging voltage and capacitance (Measured in Farads).  Capacitance is a measure of how much energy can be stored in a capacitor.  A typical power supply capacitor or audio coupling capacitor would have a capacitance of around 0.0001 farads, which is relatively large.  A super capacitor normally has a capacitance of between 1 to 3000 farads, which make them good substitutes for batteries!  We are going to safely charge 2x 400 farad capacitors in series up to 5.4VDC, and feed that voltage through a DC-DC booster circuit.  We are also going to employ a digital voltage display that will be able to read both the charge on the capacitor bank, as well as the voltage at the output of the DC-DC booster.  Let's go over SOME of the pros and cons of super capacitors, shall we?

1) As long as you don't charge them at a voltage higher than they are rated for, or reverse charge polarity, super capacitors can have charge/discharge cycles of 500,000-1,000,000, or more!
2) If you charge a battery and leave it in the charger, you can deplete battery memory, and it will eventually die.  The super capacitor will STOP accepting any energy once it is full.  
3) The internal ESR (Internal resistance) is extremely small in a super capacitor.  We're talking 0.01 Ohms or less.  A typical battery has an internal ESR or 0.02 Ohms - 0.2 Ohms.   Why does this matter?  If means that you can potentially charge a super capacitor in seconds, providing you have some heavy duty power supplies.  Batteries take longer to charge, and cannot discharge as quickly.
4) Batteries have a shelf life.  If left fully charged on a shelf for years, you will pick it up one day and find it dead.  Not so with the super cap!
5) Super capacitors give off no emissions, while all batteries give off some form of gas.  You can't keep your car battery in your house, but you can keep your super capacitor bank in your house =) 
6) If you cause a direct short along your super capacitors, they will not blow up or be harmed.  They are made to do just that.  However, immense heat will be created along the short, as enormous amounts of current will be very quickly dissipated.  This is also a con, because the user can be burned if not careful.
7) They are environmentally safe.
8) There are so many pros and so few cons, but we don't have time to go over them all =)

1) If you made a super capacitor big enough to replace your car battery, it would likely be 10 times the size.  Super capacitors have lots of energy storage, but need to be banked in series/parallel to achieve battery-like storage.
2) super capacitors normally have very low max voltage ratings, which means that you have to be very careful not to over charge them.  As well, what are you going to do with a 2.5v capacitor?  You have to place a bunch in series to keep doubling the voltage.  However, when you add capacitors in series, you lose capacitance.  The formula for series and parallel banking will be in the final step, so if you have time, have a look =)
3) While you need not worry about shocking yourself, as super capacitors offer so little voltage, you can burn yourself if you create a direct short on a fully charged super capacitor or bank of capacitors. 
4) Super capacitors are more expensive than batteries.

1) The Charging Circuit
2) The Capacitor Bank and the DC-DC Booster
3) The Digital Voltage Display
4) The Parts, the Math and the Conclusions!

If you are interested, most of these parts can be found in my ebay store, which can be found here:

Check Out My Improved 1.5A 18 Watt Charger!


Let's go through this in steps.  It is actually very simple but you have to follow along closely, especially as we go into the step on the following page. 

We start at TERMINAL BLOCK#1 and will continue clockwise around the circuit!
1) This is where you have options.  We need a DC source of anywhere between 5VDC-20VDC for our charge.  I use a 11VDC@1A power supply, but I occasionally use a set of mini solar panels that I have in my window.  The choice is yours.  Just make sure that when you plug in your DC source, you are making sure that you have the correct DC polarity for DC+ and ground (DC-). 

2) We have a 0.1uf capacitor and a 100uf capacitor in parallel with the input DC line.  We only really need these because this line is for the charging of the capacitor bank, but we will be using this input line to power our digital display and we want to make sure that this DC line is smooth and without extra noise.  The 0.1uf capacitor takes care of high frequency noise, or rather, lessens it (Decoupling capacitor).  The 100uf capacitor acts to smooth the input DC.  These two capacitors are not really necessary but they are preferred. 

3) The LM317 is a variable DC-DC power supply.  Using a 240 Ohm resistor in parallel with the VOUT and the ADJ line, and a 5k ohm variable resistor from the ADJ line and ground, we can vary the charge voltage from the charge voltage itself, down to 1.25v.  For instance, if we have 8v at the input, we can vary the output anywhere between 8v down to 1.25v.  It is EXTREMELY important that your LM317 is properly heat sinked, as it will get HOT.  The LM317 kit can be found here:

4) Varying the current to the super capacitor bank is the name of the game.  This is where you have the opportunity to gamble.  Since the super capacitors will literally suck up all the energy it is given until full (With >0.01 Ohm ESR), we have to limit the current from the supply, or else we're going to completely destroy our LM317 circuit.  As you can see, we have two 2.2 Ohm, 5W power resistors, a jumper, and a SPST (Single Pull Single Throw) switch.  If the switch is off (Recommended), and the jumper is not attached, then the charge limitation is 2.2 Ohms.  Wait a minute!  That is too small of a current limiter!  You're still going to hurt your LM317!!!  Not the case!  If properly heat sinked, the LM317 will get hot but it will withstand the stress if you have this 2 Ohm load. The output voltage will drop down but you will see it come back up as the capacitor starts to charge.  We have three charge options here.  If you have a charge of 4v or higher, make sure that you have the jumper off, and the switch off.
A) Charge limited by 2.2 Ohms when JUMPER=OFF/ SPST=OFF
B) Charge limited by roughly 1.1 Ohms when JUMPER=ON/SPST=OFF
When you add the jumper, you place the two 2.2 Ohm resistors in parallel with one another, bringing the parallel resistance down to half.  Please note that these resistors get hot.
C) Charge limited by the line resistance and capacitor ESR only when JUMPER=ON or OFF/SPST=ON  
If the SPST is switched on, it doesn't matter how the resistor jumper is configured.  The only resistance between the output of the LM317 and the capacitor banks is the line (trace) resistance, and the ESR of the capacitors (Yet to be seen).  This is where you have to have cohones!  Again, your LM317 can handle this if properly heat sinked (Heat sink included in kit), as the output voltage will drop down to the cap voltage and start to charge.  However, this should only be used for charges of 1.5v or less.  If you are charging the bank from 0v to 5.4 v, it will charge relatively quickly using the 2.2 Ohm charge option.  However, around 3v of charge, it will start to slow down.  At this point, take the jumper off to limit the current to 1.1 Ohm.   At around 4.5v, you will notice that the charge will slow down again.  Flick the switch to charge the remaining 900mv, and you will have no problems.  Truth be told, I've charged from 2v to 5.4v with the switch on, but it is NOT good practice, and I was risking my LM317.   

5) We have two IN4001 diodes in series with the charge line.  These are not used for any type of rectification, but rather to allow DC charge to enter the capacitor bank, but not allow for any DC to travel backwards through the circuit after the capacitor bank is charged.  If we didn't have these diodes here, follow the circuit backwards.  Regardless of whether the jumper is on or off, or whether the SPST is on or off, there is a path back to the LM317, and there is a 240 Ohm resistor in a series path with a 5k potentiometer and ground.  If we stopped charging (without the diodes), the charge on the caps would leak back through the circuit to ground, making our batteries terribly inefficient.  There are two diodes in parallel to share the current along the line.  If you have 1N4007s, or any 1N400X diodes, they will work just as well if not better.  There are factors such as thermal runaway that we could spend time worrying about with these diodes in parallel, but the charge time from start to finish for this circuit is literally 10 minutes or less , so we're not going to worry about that at all. 

6) The jumper (JUMPER#2) like a lot of this circuit is a custom option.  If you are not going to watch the digital display (Seen later) as your super capacitor bank charges, then you are going to want to follow this step.  When you build this charge circuit, probe the output of the diodes (TEST POINT) with reference to ground using your multimeter.  There will be a voltage drop along the diodes, so we need to make sure that we measure here, and not at the anode end of the diode.  Since we have a 5.4v MAX capacitor bank, we DO NOT want to have a charge higher than 5.4v.  Check the voltage here using the 5k potentiometer at the LM317.  Turn the potentiometer until you see a voltage of 5.2v-5.4v, then consider using a bit of hot glue to set the pot to steady it.  You may think, why use the pot, and not a fixed resistor?  You can, by all means, but you may want to change the charge voltage down the road.  Now, the jumper is here because on the other side of the jumper lies the capacitor bank.  If you test the voltage here when you have the jumper on, you will read the voltage at the capacitor bank, not the voltage that it will be charging to.  You only take the jumper off when you want to take a charged reading.  Leave it on at all other times.

Step 2: The Capacitor Bank, and DPST Switch, and the Booster Circuit

As you can see, we have the capacitor bank circuit here on the left hand side of the below schematic.  It is comprised of 2x 400 farad 2.7v super capacitors, found here:
When connected in series, these capacitors will form a bank value of 200 farads at 5.4v.  This means that we have doubled our maximum charge voltage (2.7v *2 = 5.4v), and halved our capacitance from 400 farads down to 200 farads.  If you want to learn more about series/parallel capacitor theory, go to the final page of this instructable.  We need approximately 3.4v to power our DC-DC booster circuit.  This means that our booster circuit will work between the charged range of 3.4v to 5.4v, which means we can afford 2v loss before the booster circuit cannot boost anymore.  There is an arrow coming from the positive side of the capacitor bank that indicates that this is the charge reference.  This is just an indicator and is not connected anywhere.

Just to the right of the capacitor bank, you will see what looks like a piece of lego with 6 little holes in it.  This is my own little schematic symbol for a Double Pull Double Throw switch.  As you can see, there are little arrows coming from the upper and lower middle circuits.  These are the wipers (or PULLS).  When in the off position, the wiper on the top is connected to the upper left pin (as seen in the picture),  As well, when in the off position, the bottom wiper is connected to the lower left pin (as seen in the picture).  When you press the DPDT switch on, the wipers connect to the pins on the right hand side.  These switches are independant of one another, but are located in the same package, and are switched on and off at the same time.  These only cost a buckand can be purchased with anything from my store. 
The top switch (Top left, middle and right pins) act to connect power to the DC-DC booster board.  The bottom switch (Bottom left, midle, and right pins) act to supply the digital voltage reader with either the charge voltage of the capacitor bank (when switched off), or the DC booster output voltage (when switched on).  The digital voltage reader will be talked about more on the next page.  This switch business may sound tricky, but follow along with the schematic, and you'll be in good shape =)  

This is where things start to get easy!  As stated earlier, this DC-DC booster circuit will boost any voltage at the input between 3.4v MIN to 34v MAX to any voltage between 3.4v and 34v.  The output can be adjusted by using an on-board variable resistor.  All you need is to turn the pot!

VIN = 3.4v  VOUT = Any voltage between 3.4v and 34v 
VIN = 28v   VOUT = Any voltage between 3.4v and 34v
VIN = 8v     VOUT = Any voltage between 3.4v and 34v
VIN=3v       VOUT = 3v  (Input voltage is to small to boost)

These booster boards are available in my store:
There is a three-pin screw-type terminal block for safe connection, and a variable resistor that allows for you to change the output voltage for your desired application. The three pints are labeled VOUT/GND/VIN. So, VOUT is your varied output, GND is common ground, and VIN is your input voltage pin; requiring at least 3.4VDC. It is VERY easy to use. DIMENSIONS: 32x34x20mm. It can supply up to 3A of current, but that is not suggested for continuous draw. It is highly suggested that you keep continuous draw under 2A. This bad boy is rated for 15W and has an efficiency of 90%.   As you can see, when the switch is flipped on, power is connected to the VIN terminal of the DC-DC booster board.  The second terminal of the board is connected to the ground line, and the third is connected to our output terminal block.  There is an arrow coming from the output line that is labeled "BOOST REF".  This is just for reference and is not actually connected elsewhere in the circuitry.

The terminal block (TERMINAL BLOCK#2) output can be used as our battery terminals.  The DC value at this terminal block is adjusted using the on-board variable resistor on the DC-DC booster.  

Step 3: The Digital Display

This is one of my favorite characteristics of this circuit.  The 0-20v digital digital display is easy to use, and will act to show us both the capacitor charge voltage and the DC-DC booster output voltage.  This circuit requires roughly 8-14VDC to operate.  Both of the bottom pins are connected to the ground line.  The upper left pin is the DIGITAL DIISPLAY REFERENCE.  The voltage at this pin will be displayed digitally on the display.  The digital display will display any voltage between 0-20VDC.  When the DPDT switch is not connecting the capactor bank voltage to the booster circuit, the digital display will be displaying the charge on the capacitor bank.  When the DPDT is switched on, the output of the booster will be displayed.  Since the display has a 20v maximum limitation, it is suggested that if you are going to implement it, that you keep the booster output limited to 20VDC or under.

The voltage at the upper right pin is the line that powers the entire display.  This can be hooked directly to the input DC voltage line. It will work anywhere from 6.5v to 15, but it is preferred that you use 8-14v.  The 0.1uf and 100uf capacitors that are placed at the DC input are implemented for the sake of protecting this digital display.  When you stop, disengage the DC input charge, this display will shut off. 

If you want, you can add a monotary push switch between the DC-DC booster and the power line of the digital display.  This will enable you to have a look at the output of the DC-DC booster when you push down and hold the monetary switch by adding secondary power supply for the display.  However, if you choose to go this route, it is necessary to add a diode into the mix.  If you want to go this route, as I did in the circuit viewed in the video, let me know and I'll include another schematic.

Step 4: The Parts, the Theory, and the Conclusions

I can offer a kit that includes the bulk of the parts in the schematic for $90 + $12 shipping.  The LM317 kit, the 400f super capracitors, the digital display, and the DC-DC booster board cost more than $90 in total.   If you are looking for parts singularly, they can be found here:

I'll include the following for $90 +$12 for shipping with tracking:
2x 400f 2.7v super capacitors
1x LM317 DIY kit
1x 0-20v Digital display
1x 3.4v-34v DC-DC Booster board
1x DC plug (input and port set)
2x 2.2 Ohm power resistors
2x 1N4001 diodes
1x DPDT switch
1x 0.1uf capacitor
1x 100uf capacitor
The Jumpers, terminal blocks, PCB, Input DC source, and SPST switch will not be included.  Send me a message if you are interested.  You can also reach me through and through ebay.

Most of the basic circuit theory was covered in the instructable.  However, I'll go a bit further in depth regarding super capacitors.  When you place a super capacitor in series with another super capacitor, you can up the voltage; doubling it, if the two capacitor voltage values are the same, but you lose capacitance.  The formula for lost capacitance is the same as the parallel resistor formula:   1 [ (1/  C1) + (1 / C2)]   Let's use it in the example of this instructable, where C1 = 400f, and C2 = 400f

CTotal = 1/[1/ C1) + (1 / C2)] 
CTotal = 1/[400) + (1/400)]
CTotal = 1/0.005
CTotal = 200 f

Example#2 (C1 = 3000f @ 2.5v / C2 = 10f @ 2.7fv)
First, add the two voltages.  (2.5 + 2.7 = 5.2v)  This is your max charging voltage.

CTotal = 1/[1/ C1) + (1 / C2)]
CTotal = 1/[3000) + (1/10)]
CTotal = 1/0.100
CTotal = 9.97f
The total capacitance is always lower than the lowest capacitance added to the series string, so beware.  Play around with this.  A good way to check your answers is to play with this capacitor calculator:

When placing capacitors in parallel with one another, you are looking at much easier calculations.  When you place a capacitor in series with another capacitor, you just add the two capacitances together, and that will be your total capacitance.  The maximum voltage you can charge to is always the lowest value. Let's use three capacitors in our example:

Example: (C1 = 2.0v @ 10f / C2 = 2.5v @ 100f / C3 = 2.7v @ 1000f)
Max voltage charge is 2.0v (The lowest of the three)
CTotal = C1 + C2 + C3
CTotal = 10f + 100f +1000f
CTotal = 1110f

You can also place strings of sets in series, in parallel with one another for the sake of compensating for lost capacitances.   Let's say we have 9x 2.7v @100f capacitors.  We want a capacitor that is higher than 7VDC and has the most capacitance possible.  If we place three if these 2.7v capacitors in series, we get 8.1v, but the capacitance of the string is only 33.3f.  We have 9x of these capacitors, so if we make three strings of three, and place them in parallel with one another, we have a capacitor bank that has a value of 8.1v @ 100f.  Neat, eh?  See one of my capacitor bank videos here:
There is so much theory that goes into capacitors.  If you guys have a specific question, or perhaps a project idea, I will consider building it and displaying it for you all, right here on

This circuit was a prototype, and I will be using it for years and years to come.  I have a solar panel on my window that allows for me to listen to music using free energy all day long, and even for a few hours after the sun goes down. 

There are two things I'd like to do with my next version.  I'd like to create a bank that employs thousands of farads, has a more advanced charging circuit, and has safe-charge features that are controlled by a microcontroller that cut off a charge once the device has reached the proper level of charge.

Super capacitors are the wave of the future, relative to energy storage.  I am always looking for new ways of implementing them into projects.  If you have any questions at all, feel free to ask.  PLEASE VOTE FOR THIS INSTRUCTABLE OR SUBSCRIBE IF YOU LIKE WHAT YOU SEE!


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    Question 8 weeks ago on Introduction

    I need to augment a 400 VAC circuit with a capacitor bank that will bridge a switching outage of up to a cycle. Can anyone provide some guidance on how to do this, or where to go to learn how? Thanks!!


    Question 2 years ago on Introduction

    boa tarde, nesse circuito eu consigo ate qual tensão e quantos super capacitores consigo !! como vejo que os mesmos chegaram no limite ? por favo


    7 years ago on Introduction

    I want to build a little circuit to run 6 or 8 LEDs at night and powered by a solar cell which can charge all day long. I want to store the energy in Supercapacitors during the day and run the lights at night. How many farads do I need to power the lights for a few hours?


    Reply 2 years ago

    What you are suggesting is a form of perpetual machine. It woun't work.


    3 years ago on Step 4

    Using LM317 to charge the capacitors is a bad idea as you run it in "protection" mode, meaning you use its over-current protection to limit your charging current. This is why it gets so hot and this is not a good way to charge those capacitors. You should replace that with CV-CC module, which not only keeps the voltage at the value you want, but also limits the current to a value you want. It doesn't cost much more and is a much more safe solution. This way you also get rid of the power resistors, which only waste energy.
    Also it is not a good idea to connect capacitors of different type (different nominal voltage, but also different models) in series. You calculate the voltage, but the actual voltage over each capacitor when charging will depend on internal resistance of each one of them, therefor you risk damaging some of them. Best thing to do is always you the same model capacitors when you make packs.

    jose abreu monteiro
    jose abreu monteiro

    4 years ago

    Thank you! I learned a lot with your clarifications about recharging! I want to ask two questions:
    1) If the charger continues to send voltage (2.5 volts for prevention) and amperage to a supercapacitor will it skip because it is already charged or will it explode?
    2) The fact that I do not charge with 2.7 volts, but with 2.5 volts does this imply that I will have less amperage in this supercapacitor, or will the amperage be the same for any voltage?
    Jose Monteiro from Brazil


    4 years ago

    Cn i use it as a bicycle 36v battery replacement?


    Question 4 years ago on Introduction

    Looking for an alternative solution.

    Aim: to replace +/- 5 v regulator with high PSSR 90 db. 500-600 milli amps

    Current: 5v supply from M5F78M05 or NJM78M05 linear regulator

    I am looking for a solution to the above using Super Capacitors equivalent or a Virtual Battery Operation designed circuit.


    5 years ago

    sir i want to store energy upto 50 millijoule from voltage source 3.5volt. but this voltage source is renewable type . plz suggest some circuit for storing energy


    6 years ago

    I would suggest buying a switching current limiter, you're paying that much pay a few more dollars (2$?! I found mine for around 2-3$) and mine didn't generate even the tiniest amount of heat while charging at 2A! (mine is 50F! charges my phone for 2 minutes :c)


    6 years ago

    I need for PV to run a motor advice.


    6 years ago

    If i just want to charge the capacitors , without the DC-DC convertor and LED screen , can i just use the charging circuit ? I'm making an RC car and i dont need al these extras . I just need a power supply that can charge fast .

    Super experiment. But why do people still use the lithium ion polymer batteries? Why aren't mobile phone manufacturers switching over to super caps?


    Reply 6 years ago

    If you have the money or if you Can use a 24inch phone you can make one :)


    Reply 7 years ago

    Capacitors are way bigger than the batteries.


    Reply 8 years ago on Introduction

    because supercapacitors are ten times less energy dense than batteries. so a supercapacitor with the same capacity as a battery will be ten times larger. supercapacitors are also 10x more expensive.

    not to say that it's not being done... SCs have already found their way into power tools. research on SCs is very active. wait for supercapacitor-battery hybrids on your phone in a couple of years

    saran ashvi07
    saran ashvi07

    6 years ago

    How long it gives power and what about the self discharging of the super cap


    7 years ago