Super Capacitor Battery

THIS INSTRUCTABLE WILL BE BROKEN DOWN INTO 4 PARTS: 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!

Step 1: THE CHARGING CIRCUIT

THE CHARGING CIRCUIT:
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.
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

THE CAPACITOR BANK:
As you can see, we have the capacitor bank circuit here on the left hand side of the below schematic.
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.

THE DPDT SWITCH:
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 =)  
 
THE DC-DC BOOSTER:
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!

Examples:
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)
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

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.

OPTION:
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

THE PARTS:
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.

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.

THE THEORY:
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

Example:
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.

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 instructables.com.

CONCLUSIONS:
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!


THANKS EVERYONE!