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:  http://www.electroniclessons.com/

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: http://cgi.ebay.com/DIY-LM317-Variable-DC-power-supply-kit-PCB-Parts-/180609634986?pt=LH_DefaultDomain_0&hash=item2a0d2c52aa

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.

About This Instructable


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Bio: 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 ... More »
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