# Let's Learn About Super Capacitors! (A Practical Guide to Super Capacitors)

362,464

548

101

Published

## Introduction: Let's Learn About Super Capacitors! (A Practical Guide to Super Capacitors)

Hi Instructables Community!

CHECK OUT OUR SUPER CAPACITOR FLASHLIGHT KICKSTARTER CAMPAIGN:
http://www.kickstarter.com/projects/172204344/the-forever-rechargeable-talking-super-capacitor-f?ref=live

LET'S TALK ABOUT SUPER CAPACITORS!
Thanks for looking at my instructable!  This instructable will be a little bit shorter than some of my others, and it will be written from the perspective of a technician, not an engineer.  This instructable will be followed with similar super capacitor related instructables.  I'm not going to blast super capacitor noobies with a ton of flashy math.  However, I will be providing links to sites where math can be found for those of you who are interested.  I want to keep this document as practical as possible. There are some fun videos in STEP#8 and some links to my hobby electronics stores in STEP#9.  For those of you who don't know much about super capacitors, here is a little bit of fun theory:

THEORY:
Super capacitors act like any other kind of capacitor, only they can store tremendous amounts of energy.  Many capacitors that you'd have seen in audio circuits have capacitances such as 470uf or 680uf (micro farads).  Capacitors used in high frequency RF applications can be as small as 1pf (pico farad).  The farad is a measure of capacitance (or storage capacity).  They are often used in filtering applications, coupling or decoupling applications, or AC-DC smooting applications (there are some large caps in your standard AC-DC power supply that acts to smooth out the ripple on the line).

Super capacitors can be used in solar power applications, battery back-up applications, battery applications, flash-light applications, etc.  Aside from the fact that the super capacitor can be charged very quickly due to their low internal resistance, which is known as ESR, but they can just as quickly be discharged.  Batteries contain harmful chemicals, and die over time.  If you handle your super capacitors carefully, you will die before they do...Seriously!  Howver, there are rules...

Super capacitors do not give off gas like lead acid batteries, but they cannot store as much power either.  You can place capacitors in series or in parallel to either up the maximum charge voltage, or total capacitorance.  We will talk about this later.

Really, there is a lot to be said about capacitors, and you're not going to want to spend your entire day listing to me, so let's get down to the basics.  You can go fourth and choose which tabs you;re interested in.   Here is a video just for fun of me starting my car with super capacitors!
•

## Step 1: Understanding Capacitance

Capacitances: Capacitors Vs. Super capacitors!
Have you ever heard someone talk about nano this or micro that?  These terms can be used for voltage, power, current, resistance, inductance, etc.  When we talk about the capacitance of a capacitor, we  will do the same.  The below explanation will also help you to understand just how much capacity a super capacitor has in relation to a standard capacitor.

Understanding Capacitance Terminology:
1pf (pico farad) = 0.000000000001 farads
1nf (nano farad) = 0.000000001 farads
1uf (micro farad) = 0.000001 farads
1mf (milli farad) = 0.001 farads

The table in the image is much more detailed.  This page is an attempt to demonstrate just how much capacity a super capacitor has.  A one farad super capacitor can store one million time more energy at a common voltage, than a 1uf capacitor, one billion times more than a 1nf capacitor, and one trillion times more than a 1pf capacitor.  Cool, huh?

However, super capacitors have very small voltage ratings, such as 2.5v, 2.7v and 5.5v (Some common values).  This makes things difficult, as in order to make our capacitors capable of charging up to a higher voltage, we need to place them in series, which brings a bunch of other variables into play.  There are sections coming up on Series/Parallel configurations, as well as charging methods, and balancing methods.

You can also employ DC-DC voltage boosters.  Typical DC-DC boosters take a voltage of around 3.4-5VDC and are capable of boosting the output voltage.  We sell all sorts of boosters, super capacitors, and solar panels here:
Visit our ebay store here: http://www.electroniclessons.com/
Please check out our hobby electronic store here: http://engineeringshock.com/

## Step 2: Are Super Capacitors Dangerous?

Ah, the fear of super capacitors.  Both capacitors and super capacitors can be dangerous, but in different ways.

Capacitors *Potential Shock Hazard*:
If you have a 500v capacitor that has a capacitance of 100nf, and you touch your finger to the positive and negative lead, you can get a nasty shock.  If you have one hand grounded, and you touch the positive lead with your other hand, your body will act as a path to ground, and you will get a nasty instantaneous shock.  The capacitor will instantly discharge through you and IT WILL HURT.  I know.... It has happened to me.
Capacitors with a lower capacitance commonly have a higher charge value, often in the 100v-1000v range or higher.  However, they can't store much power.  If they're discharged, the voltage will go from 100v to 0v in an very quickly, depending on the size of load that is discharging it.  Since the voltage is so high, you can give yourself a nice shock.  Most of the time, you're not going to have to worry, but it will seriously scare the crap out of you.

Super capacitors *Potential Fire/Burn Hazard*:
Are you afraid of touching the leads of your 12v car battery?  You need not be, and for two good reasons.  The DC voltage on a car battery is so low that you're not going to have to worry about being shocked.  Secondly, your skin has such a high resistance.  This means that next to no current is going to pass through your body.   However, if you short the leads of a battery with a conductor, you will create a TON of heat, which can burn you (Or blow up the battery).  This is due to current, not voltage.  If you create a dead short across a battery, you will create heat.  Why?  Because a dead short will mean next to no limiting resistance between the positive and negative lead, which means that current is not being limited, which means that the battery will supply as much current as it can, which will create a ton of heat.  Car batteries will blow up if you do this.  Super capacitors will not.   If you have a 12v capacitor bank with a 20 milli ohm (0.02 Ohms) internal resistance, and you short the leads, you're not going to hurt the caps.  They are built to discharge much faster than batteries, as batteries have a higher ESR.  However, if you short the leads with a conductor, the conductor is going to go RED with heat, which can set fire to the insulation of the wire, or severely  burn anyone who touches it.  Believe me, as again it has happened to me

Example#1
I have a 12v super capacitor bank, and I touch my right hand to the negative lead, and my left hand to the positive leads.  The resistance of the path from my left hand through my body to my right hand is more than 2,000,000 Ohms.  The current being passed through my body will be:
Current(I) = Voltage(V) / Resistance(R)
I = 12v / 2,000,000 Ohms
I = 0.000006 Amperes (6uA)

Example#2
I have a 12v super capacitor bank, and I short the leads with a conductor that has a resistance of 0.2 Ohms. The current along that conductor will be:
I = 12v / 0.2 Ohms
I = 60A (60 freaking amperes)
Means that there will be a TON of heat dissipation along the leads.  This happened to me with a 12.5V 96 farad capacitor bank,and the insulation on the wires set fire.

NOTES:
1) If you short a car battery, it will likely explode.
2) If you short a capacitor bank, a ton of heat will be created along the conductor, but they will not be damaged.  They are created for extremely fast discharges, and high current applications at lower voltages.  Just be careful not to burn yourself.

Treat your capacitors with respect, and you're going to have a good day =)

## Step 3: The Rules You Must Follow!

Super capacitors are like gremlins, or perhaps like the Mogwai!  You must follow certain rules or you're going to regret it!  If you follow the rules, you're going to have happy capacitors that lead extremely long lives, and give you more bang for your buck!

The Rules:
1) You must never charge past the capacitor voltage rating.  If you have a 2.5v super capacitor, you must NEVER charge it at a higher voltage.  If you do, you risk damaging the integrity of the capacitor, or worse, an explosion.  Personally, I never charge past 80-90% of the rated charge.  If you have a capacitor bank of say 15v, never charge that bank past 15v.  I would personally charge that bank to 13-14v MAX.

2)  If you have a 5.4v capacitor bank, and you are charging that bank with a 5v-5.4v charge, you can leave them unsupervised and go have a snack.  Unlike batteries, you don't have to worry about the capacitors having a charge memory issue.  When the capacitor bank is full, it will stop accepting energy.  It will NOT hurt the capacitors if you keep a charge on them at all times, as long as you are not charging the super capacitors at a voltage higher than they are rated for, or that the bank is rated for.  Batteries on the other hand, will lose integrity if left in a charger for too long.  Another reason why super capacitors are so awesome!

3) If you are charging super capacitors, you will  have to be careful.  Not for your own safety, but rather the safety of your power supply.  Super capacitors will take in as much current as humanly possible, and will look like a dead short on your power supply, which can cause fuses to blow.  You will have to limit the charge to the super capacitor(s).  See the "HOW TO CHARGE" section for more information.

4)  FOR THE LOVE OF GOD, DO NOT REVERSE POLARITY!  Some smaller capacitors have are non-polarized, while some are (electrolytic capacitors).  When a capacitor is polarized, it means that it has a positive (+) and negative (-) lead.  The positive charge must be applied to the (+) lead, which is typically longer than the (-) lead.  the (-) lead should be connected to DC ground.  If you reverse polarity, you will not only risk losing your super cap, but you will risk an explosion.

5) If a super capacitor is discharging a ton of current, do not touch the leads.  They may not be red, but they can still burn you!

## Step 4: Paralllel Capacitor Banks

Super capacitors can be placed in parallel to up the capacitance of the circuit.  You can even place series banks in parallel with one another.   However, there are a few things to consider.

1) If you place two capacitors in parallel, the voltage ratings do not have to be the same.  However, the parallel bank should never be charged past the rating of the smallest capacitor.  For instance, if you have a 2.7v super capacitor, and you place it in parallel with a 2.5v super capacitor, you will never want to charge the bank past 2.5v.  We will call our maximum charge voltage VT.  If you have two strings of capacitors in series, you can place them in parallel with one another, but if the voltage ratings of the banks differ, you have to make sure that you regulate the charge voltage to be just under the voltage rating of the smaller bank. If you have a 5v capacitor bank, and you want to place it in parallel with a 10v capacitor bank, you MUST NOT charge past 5v.  Personally, I never charge past 80-90% of the lowest charge.

2) To determine the total capacitance of a parallel bank, You simply add the capacitances together!

Example#1
You have three capacitors in parallel with one another.  The first has a capacitance of 6800uf and has a max charge voltage of 25v. The second is 1f capacitor rated for 2.7v, and the final capacitor is 3000f rated for 2.5v.  You simply add the capacitances together:
CT (Capacitance total) = 0.0068 + 1 + 3000
CT = 3001.0068 Farads
VT (Charge voltage) = 2.5v (The smallest capacitor charge voltage)

Example#2
You have two series capacitor banks.  The first is rated for 200f at 15v, and the second is rated for 1000f at 12v.
CT = 200f + 1000f
CT = 1200f
VT = 12v (The smaller capacitor bank charge voltage rating)

Example#3
You have two series capacitors in parallel.   The first is rated for 12f at 5.5v, and the second is rated for 2600f at 2.5v.
CT = 12f + 2600f
CT = 2612f
VT = 2.5v (The smaller capacitor bank charge voltage rating)

Series / Parallel Capacitor Calculator: http://www.electronics2000.co.uk/calc/series-parallel-capacitor-calculator.php

## Step 5: Series Capacitor Banks

A lot of the theory behind placing super capacitors in series will tie in to STEP#7, which talks about balancing circuitry.  Most of you guys are going to want to place your super capacitors in series, so that you can create higher voltages for your projects.  When you place capacitors in series, you can up the charge voltage.  However, you sacrifice some of your capacitance when you do this.  As well, you will need to consider balancing options.

The Simple Math:
The maximum charge voltage (VT) of a series capacitor bank is found by simply adding the voltage ratings of the series capacitors together.  The total capacitance (CT) of a series bank is found using a special formula.  If you're familiar with paralleL resistor theory, you're going to have no problems here.  The foruma for your capacitance total in series is:
CT = 1/[(1/C1)+(1/C2)+....(1/CN)]     NOTE: CN is the last capacitor in the bank.  Okay, that looks complicated....  Let's go through a few examples.

EXAMPLE#1
We have two capacitors in series.  The first capacitor is a 100f 2.7v capacitor.  The second is also a 100f 2.7v capacitor.
VT = 2.7v + 2.7v
VT = 5.4v
So we can charge our bank up to a MAXIMUM of 5.4v.
CT = 1/[(1/100f)+(1/100f)]
CT = 1/[(0.01)+(0.01)]
CT = 1/(0.02)
CT = 50f     That's right!  If you place two capacitors of the same calacitance value, you're total capacitance will be half!
So your capacitor bank will be rated for 5.4v at 50f!

EXAMPLE#2
To keep things simple, let's add a third capacitor of the same value into the equation.  We now have tthree capacitors in series. All three capacitors are rated for 2.7v at 100f.
VT = 2.7v + 2.7v +2.7v
VT = 8.1v
So we can charge our bank up to a MAXIMUM of 8.1v.
CT = 1/[(1/100f)+(1/100f)+(1/100f)]
CT = 1/[(0.01)+(0.01)+(0.01)]
CT = 1/(0.03)
CT = 33.3f
So your capacitor bank will be rated for 8.1v at 33.3f!

EXAMPLE#3
L
et's try something a little harder, shall we?  We have four capacitors in series.
CAP#1 = 2.5v @ 10f
CAP#2 = 2.7v @1f
CAP#3 = 5.5v @ 0.47f
CAP#4 = 2.7v @ 3000f
VT = 2.5v + 2.7v + 5.5v + 2.7v
VT = 13.4v
So we can charge our bank up to a MAXIMUM of 13.4v.
CT = 1/[(1/10f)+(1/1f)+(1/0.47f)+(1/3000f)]
CT = 1/[(0.1)+(1)+(2.1276)+(0.000333]
CT = 1/(3.2279)
CT = 0.31f
WHAT THE HELL?  Yes ladies and gents, your total capacitance will ALWAYS be lower than the capacitance of the LOWEST capacitor in the bank when working with series banks; in this case 0.47f.  Try a few more examples for yourself!  Here is a very simple super capacitor calculator:

Series / Parallel Capacitor Calculator:  http://www.electronics2000.co.uk/calc/series-parallel-capacitor-calculator.php

PLACING SERIES BANKS IN PARALLEL:
You can place two series banks in parallel. To compensate for lost capacitance! I've done this on several occassions. If you have two series banks or more, look at each bank as a single capacitor. If you place two banks in parallel, think of them as two separate capacitors, and follow the rules of parallel capacitors. For example, if we have two series banks of 1000f 12v capacitors and we place them in parallel, we will have a 2000f 12v bank. Here is another example. You have three series banks:
Bank#1 = 1200f 14v
Bank#2 = 3000f 12v
Bank#3 = 4000f 10v
When you place these banks in series, you will have a 8200f 10v bank. Simple, eh?

PLEASE NOTE THAT THERE ARE PAGES THAT ARE DEDICATED TO CHARGING SUPER CAPACITORS, AS WELL AS BALANCING SERIES CAPACITORS!  CHECK THEM OUT!

## Step 6: Charging Your Super Capacitors

When charging your super capacitors, you have to take several things into consideration.  Some of which we've already covered.

1) If you are using a power supply that is protected by a fuse, you have to limit the charge from the power supply from the power supply to the capacitor bank.  For instance, let's say that you have a 300 farad capacitor bank that you want to charge to 6VDC.  You have a 6v power supply that is capable of sourcing 1.2A MAX current before the fuse blows.  For safety sake, let's find the right resistor that will limit the current to 1A:

Calculations:
Charge resistor value = 6v / 1A = 6 Ohms - Simple Ohm's law: R=E/I
Now, let's talk POWER (Wattage)!
Resistor Power = 6v x 1A = 6W  (Power = Voltage x Current)
In order to charge our 6v capacitor bank at 1A with the 6v power supply, you're going to need a 6 Ohm resistor with a wattage rating of 6W or higher.

How long will it take to charge:

This might vary a little bit because all capacfitors have a large tolerance, which is around 10-20%; meaning that the rated capacitance can be higher or lower by 10-20% than the rating labeled on the side of the capacitor.  As well, your resistor will also have a tolerance, but not as large.  There is a lot of math involved with time constants and the relationship between the capacitor and resistor.  If you are interested in timing, check this link out:  http://physics.bu.edu/~duffy/semester2/c11_RC.html
You will find it to be very helpful!

If you are using a solar panel to charge your capacitors, you need to make sure that the panel is matched to the capacitor bank.  By this, I mean that if you are using a 12v solar panel, you're going to want to make sure that your bank is rated for 12v or higher.  Preferrably 15v to 17v to be safe.  You're also going to want to use a diode in series with the positive lead of the panel and the positive lead of the capacitor bank.  You can see an example of this in STEP#7.  This diode is used to ensure that there is no back-powering from the capacitors back through the solar cell.

If you are going to use a DC crank generator, you're going to want to make sure that you use the diode as well.  If you do not, all of the power you generate will be lost back through the motor windings, and you're not going to get anywhere!  The diode is EXTREMELY necessary!  I will be creating new instructables based on super capacitors that go more into depth on this topic.  Feel free to watch the below videos.  I go into detail as to how I designed my chargers.  There are three of them displayed for you in these videos.

There are also ICs that are available with on-board balancing circuitry that can help you on your way, such as this IC:
http://www.linear.com/product/LTC3225

This video shows you one of my smaller programmable super capacitor chargers.  One day, I will make an instructable for this.  It employs a PIC10 MCU with an internal ADC:

This next video will show you a fully tuneable super capcaitor charger that can charge to any four voltages between 0-15VDC.  This one was a lot of fun to make!

This video shows you my first super capacitor charger.  I've since completely re-engineered this since I took this video.  Still, it should you how I go about charging.

## Step 7: Balancing Your Series Banks

Ah, the never ending debate about balancing your super capacitors.  This is a tough one, and I'll tell you why.  There are many different methods of balancing for super capacitors, but it seems that everyone has a different preference.  This information can be hard to find.  As well, most methods of balancing will limit the charge and discharge limits of your super capacitor.  Meaning that you will possibly negate the function of the balancing circuit, or damage your balancing circuit if you charge at a high current, or discharge at a high current.  Custom balancing circuits are available, but they are expensive, and still have limitations.  Yes, even for Maxwell balancing circuits.

Personally, I prefer to make a bank and charge it to only 75-80% MAX of the total charge voltage.  For instance, if I have a 15v bank of capacitors in series, I will only charge to 12.5-13v.  This will slightly waste on capacity, but you're not going to have any over-charging issues, as all of the caps in the bank will all be charged to 75-80% of the maximum charge.  You can try this for yourself.

There are many other options, such as using a resistor divider network, diodes, and active bleeder circuits.  I've found a wonderful little forum discussion (Thanks to ultracapacitors.org).  The problem with zener diodes is you will need high wattage zeners that will likely require heat sinks.  The problem with the resistor divider network is that you will either have to implement high resistance resistors and charge EXTREMELY SLOWELY, or use high wattage low-resistance resistors, and you will bleed a TON of energy off in the process.  There really is a lot to it.  The problem is that most balancing circuitry theory is based around capacitors that are extremely small in comparison to super capacitors.

See this link for forum discussion:
http://www.ultracapacitors.org/index.php?option=com_fireboard&Itemid=99&catid=8&func=fb_pdf&id=2247

If you are willing to sacrifice some capacity, then my preferred method is the way to go.  I plan on doing some experiments in the future, but instead of providing direct information that I have not personally verified, I suggest having a look through the document posted above.  This is a very heated topic of conversation.

When in series, the voltages on each capacitor will vary mainly due to each individual  leakage current.  It is HIGHLY recommended that you use the same capacitance values in your series banks.  This is because if you have a capacitor with high capacitance and a capacitor with low capacitance, they're going to discharge at different speeds based on the load.   Some have more than others which leads to voltage imbalance.  If you measure the voltage on each individual capacitor in a bank, you will see just this; different voltage on each of them.  Again, if you only charge to 75-80% of the maximum charge, you're going to have different voltages on each of the capacitors, but they will all be well within the charge limit range.

IN REGARDS TO THE SCHEMATIC POSTED FOR THIS TOPIC:
Many thanks to David A. Johnson P.E . (Professional Engineer) for this circuit.  The document behind this circuit can be found here:
http://www.discovercircuits.com/DJ-Circuits/supcapvoltlim.htm

By far, this is the best balancing circuit I've come across.  It is a custom circuit for a 3v load, but it can easily be modified to suit other needs.  I'll go through the circuit theory, but be sure to check out the link above!  The 9v 300mA MAX solar panel is charging a set of three super series super capacitors.   The 1N5819 diode blocks power from entering back through the solar panel.  The charge off the super capacitors enters into a 3v regulator that powers the load (Load circuit not seen here).  When using solar panels, you don't necessarily have to limit the charge with a resistor, as you won't damage the solar cell if drawing ALL of the energy it is creating.  When using a wall transformer combined with say an LM317 variable DC power supply IC, it is EXTREMELY important to use a charge limiting resistor.

Each capacitor has its own charge limiter circuit, and I have to say that it is ingenius!   Each of the three capacitors is tied to a comparator circuit.  Each comparator circuit acts to drain the capacitor down to 2.65v if the voltage at the positive input surpasses 1.2v.  This is where customization comes into play. You can use this circuit as a reference, and really go to town with your modiification.  These capacitors have a charge limit of 2.7v.  The engineer who designed this wanted each cap to be charged to a maximum of 2.65v (Three of them is series would equal 7.95v).  That 7.95v is then fed into a 3v voltage regulator, which is redundant for this discussion.   There is a 33k ohm protective resistor in series with the 1.2v zener diode that sets the 1.2v reference at the negative input of the comparator.  At the positive input of the comparator, there is a resistor network that is comprised of a 75k and a 68k resistor.

Some Calculations:
2.65v / (75 + 68) = 0.01853...
0.0185 x 68 = 1.26v (roughly)

This calculation means that when we see the voltage on the capacitor rise to 2.65v, we see more than 1.2v at the positive input.
When there is 2.65v or more on each capacitor, there will be roughly 1.26v at the positive input of the comparator.  When there is more voltage at the positive input than there is at the negative input, the comparator output is turned on, activating the FET, which drains the voltage down to less than 2.65v.  When the voltage on the capacitor is less than 2.65v, the voltage at the positive input of the comparator is lower than the voltage at the negative input, which then turns the comparator off.  When the comparator is off, the FET is not draining.   The current being drained along the FET is limited by a 2.2 Ohm 1W resistor.  I believe that the 10k ohm resistor between the 1.2v zener diode and the negative input is used to eliminate an offset voltage and is recommended in the data sheet.

The operational amplifiers being used as comparators are micro powered.  This means that the VCC, or power supply voltage requirement is very low; in this case it is 1.6v-5.5v.  What is really cool about this circuit is that the DC ground is not used for reference in the top two comparator circuits.  The negative reference points are the negative leads of each super capacitor, which makes the working voltage for each circuit is the voltage on each of the individual capacitor.

## Step 8: Videos

Here are some fun videos that I created for my super capacitor designs.  Please note that we sell all sorts of hobby electronics and super capacitors at http://www.electroniclessons.com and http://www.engineeringshock.com.

In this video, we use super capacitors to power a spark transmitter that acts as a Tesla coil!

In this video, I power my CRT television with super capacitors as I play video games!

This video shows you my 2010 Halloween costume that is powered by 2x 3000 Farad boost capacitors!

Here is a video of me powering some random AC devices using my 12.5v 96 farad capacitor bank and an inverter!

Here is a video of me powering my original NES and playing Double Dragon 3.

In the following videos, you'll see my variable capacitor battery video, and videos of me powering motors, solenoids, a radio, and part of my halloween costume.

Thanks to everyone who made it this far =)  I hope you've found these videos educational.  I hope you've found this instructable helpful!  if you have any questions, I'll do my very best to answer you.  I'm a busy dude, but I'll try to keep up with any comments that pop up.

Please check out our hobby electronic store here:  http://engineeringshock.com/
Visit our ebay store here:  http://www.electroniclessons.com/

## Step 9: WHERE CAN I BUY THEM FOR EXCELLENT PRICES?

GLAD YOU ASKED!
In addition to a huge number of different super capacitors, we also have a ton of unique and fun electronic hobby wares.  Check us out!  Feel free to ask us any questions you may have.  We also do some product design, and component sourcing.

Visit our ebay store here: http://www.electroniclessons.com/
Please check out our hobby electronic store here: http://engineeringshock.com/

## Step 10: DISCLAIMER - PLEASE READ

DISCLAIMER:
Again, I want to add that this instructable was meant to be simple and fun.  There is a TON of theory that relates to both capacitors and super capacitors that have been left out for the sake of being practical.  For all of those engineering types out there, please do NOT break my balls.  I have a TON of experience with super capacitors, and I've designed many, many circuits that include them.

I WILL BE FOLLOWING UP WITH OTHER INSTRUCABLES RELATING TO SUPER CAPACITORS!

Over the next year, look for my isntructables on;
1) Super capacitor flashlight!
2) Super capacitor charger!
3) Super capacitor custom balancing circuit!

Thanks again to all of you who took the time to read this instructable!  I hope you found it insightful and fun =)

## Recommendations

• ### Large Motors Class

8,821 Enrolled

• ### Clocks Contest

We have a be nice policy.
Please be positive and constructive.

## 101 Comments

for capacitors in parallel:

Ctotal=C1+C2+C3...+Cn

for capacitors in series

1/Ctotal=1/C1+1/C2+1/C3......+1/Cn

Has anyone actually built that circuit by David A. Johnson? The SEIKO S-1131B30UC-N4PTFG LDO regulator has a Vin-max = 7.0v according to the datasheet, making a charged supercap voltage of 7.95v a fine way to destroy that SEIKO regulator. I then simulated the circuit in LTspice (substituting a resistor in place of the SEIKO regulator) only to find the voltage across each of the 3 supercaps is in fact 2.928v, which will cause those caps to explode. Here is my LTspice circuit for anyone to test:

https://cl.ly/ptjj/DaveJohnson_SuperCap_Triple.asc.zip

Quick question. If you're fully discharging a series capacitor bank, some caps will reach 0V before the other ones in the bank. Since current still keeps flowing, the caps that still have energy in them will proceed to reverse-charge the caps that were previously at 0V. Is this very harmful to them or can they tolerate some small amount of reverse charge?

I'm asking because I have a bank of 6x 500F supercaps in series in a balancing board that bleeds off any excess voltage above about 2.66V (maximum dissipation 1A). It works fine for over-voltage protection (I tested it with a DC-DC converter before soldering on the capacitors) but my testing shows that it does not block reverse current. I was wondering if I should put a reverse-biased Schottky diode in parallel with each capacitor to protect it by behaving as a short-circuit in case the voltage across that cap ever turns negative.

Hi, can someone please help me with identification of the component from SC Balance Protection Board as shown in schem. I drew by myself? Since I don't want to wait over a month for this module to arrive in my country, I intend to put components myself. Here is the actual pic and schem. Thx in advance guys!

4 replies

Have you been able to figure this out? I have very similar boards, and mine use Q2 =2SD882, Q1=S8550-2TY-Transistor, U1 is indeed the TL431, 3x1R2 and R1 appears to be a 8,2kOhm resistor although. shouldn't there be a connection from R1 to the third leg of Q1 in your drawing?

Thanks, I already managed to find this post by A. Spiess

http://www.sensorsiot.org/simple-and-cheap-way-to-...

where he reverse engineered the circuit. I also managed to buy all these components in my local electronics stores (TL431 is in TO92 package which is probably the same thing), and will solder up these components together and give it a go. Yes, you're right, the first pin of R1 goes to the first pin of R3 and then to the emitter pin of Q1 (that's SS8550). Here's the corrected drawing!

I think I've seen videos by A. Spiess before, but not on that subject. Thanks for the link. It helps a lot.

You are welcome!

A very good tip is to use a motorcycle/Car stop/main bulb (ie 12v 6w) as a resistor in series if using a power supply. It will offer high resistance for high current (at the begging), but it will lower it's resistance as the capacitor is charged, so it will charge faster and waste less energy.

1 reply

Hi, so in my case I have two 500 F 2.7 V caps and a DC-DC Boost-Buck converter module with 5 A max. output current. I put four 1N4936 diodes in series, pos. to neg. to each capacitor in order to "balance charge" them. If I connect these two in series with also the 12 V (in my case 21 W) car bulb in series and adjust the max. output voltage to 5.4 V, will it work?

There was this one time when I accidentally reversed the polarity when charging w/ a 9v battery for about 30 mins. When I went to check on it, it was sizzling. At first I thought it was charged(this was my first supercapacitor), but common sense told me that when something is charged, it doesn't sizzle. Afraid to touch it, I shook the SC off the battery. It was then that I noticed it had brown stuff on the top. Finally, I decided to brave picking it up very carefully. It was about as hot as the time I touched the tin can after burning wood in it for 2 hrs. I didn't want to leave it on my carpet, so I picked it up in a baseball sock. Some time later, I came back to it to find it room temp. Using the sock, I scraped the brown stuff off into the trash can and found that the silver cap was still closed. This was a surprise, because I thought I had really broke my supercapacitor. I tried again with the correct polarity and it worked. Now I know from this article that you have to be careful with supercapacitors. FOR THE LOVE OF GOD, I WILL NEVER REVERSE POLARITY AGAIN!!! THAT EXPERIENCE WAS SCARY!!!!

Hi, can I put permanently super capacitors in parallel with 12V battery? For (old) car use. Any precaution to be taken? Thank you.

Hi, could you confirm I could charge a 13F 5.4v supercaps with 2.8v 3w source and discharge it at 5v? Thanks for the clearness of your explenation, even people with very little knowledge of electronics like me could understand.

If I charge a 5.4v 12.5F capacitor could I connect it to a lipo 3.7v battery and expecting supercap will discharge into it?

i want to create a 48v supercapacitor pack. so i put 18 supercapacitor in series. how to do balanced charging for this?

If they are wired in series then you have a 16.2V 58F capacitor bank. You should be able to use up to a 16.2V charger, but I think most would recommend something more conservative like 14V.

I'm building a battery tab spot welder. Lot's of info out there and people using all sorts of capacitor banks pumping out loads of energy. Consensus says 1farad at the weld is what we want for a good weld. This has to factor in a guesstimate of what the circuitry resistance will be from the capacitor bank to the probes. Amy way to ballpark guess what the loss of farads due to resistance may be? Trying to save money and be efficient in capacitor selection. Do I need to have 58F at the bank to get 1F at the weld or would I be safe with 10F at the bank to get 1F at the weld?

ERROR!

Just an awesome write up thank you for sharing.

Not sure if it has been commented upon,but Step 4 Example 2 has an error.

best.

i have 100 farad 2.7 volt capacitors so i need to charge it with 2.7 volts right?

1 reply

DenizG1 Most of the time you need to limit the current.