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.

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!

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!

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

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?


<p>Thank you, I've learned a lot from your Instructable about super-capacitors</p>
<p>is there any possibility to use supercapacitor as battery backup for electric car.... if possible please say how to proceed so.</p>
<p>if we are charging a capacitor with a fixed voltage source then there is no point of overcharging because capacitor will automatically stop charging when voltage across it will match with the supply voltage.</p><p>so would you please explain my doubt regarding your statement that &quot;we should care not to overcharge&quot;.</p>
<p>hello sir, </p><p>we are working in a solar car project,our problm is:-</p><p>1.we have to ride the car with solar power without using batteries,for a 50-70(meters),the car weighs 250kg(max).</p><p>we r using 3 solar panels and we r getting approx. 470w from it.</p><p>is it possible to drive d car with that power.</p><p>if NO, for initial torque we r going to use super capacitor,is it possible.....</p><p>please give d super capacitor values,nor possible suggestions......</p><p>i will be very much thankfull to u .....................</p>
<p>If you're actually getting 470w from your panels, that's about 2/3rds of a horsepower, With correct gearing it shouldn't be any problem... Supercaps could help it start up quickly though</p>
<p>I want to use a supercapacitor in a circuit charged by an inductor and magnet (energy harvesting coil). How can I limit the charging voltage coming out of the coil so it won't blow the supercapcitor (a diode to ground? or something) and what happens if I keep adding more current after it's fully charged (but still at the rated voltage)? Thanks for a very informative ible.</p>
<p>This is not something you need to worry about . Although for a microsecond your coil will generate high voltage this is too fleeting to cause harm ( unless it's the size of a toaster) . The high voltage is immediately dissipated, it's better to think in terms of power . Just connect the coil with a diode in series to the cap, but don't overcharge, put a voltmeter across the cap , or a single white LED, which will light up at around 2.4V.. if it's a moderately sized coil it will take quite a while to charge up.</p>
<p>......An improvement on my above reply.... The coil will not generate high voltage when connected to an empty capacitor, it's the same as if you were to short the coil, voltage low, current 'high'... the coil only produces high voltage on open circuit... the power can't get out , so 'pressure ' builds until it can, (so to speak)...but as the capacitor fills up you could reach high voltage, limited only by how leaky the capacitor is, and the efficiency of the diode....hope that helps. </p>
<p>Nice informative instructable.</p>
Nice tutorial! I've been looking around the web for some practical information about super capacitors, and this seems to be the best source so far.<br><br>I have a few questions though (which I haven't been able to find the answers to on any site thus far). <br><br>I'm working on a project that requires a temporary backup power source, and the simplest and most cost effective method seems to be through the use of super capacitors. The idea is that the caps will provide power to a microcontroller which can detect the transition to backup power. From there, it will enter a low power state (low current display, RTC, backup registers, and backup SRAM). <br><br>The current consumption is rather low, probably 100mA at most at 3.3V. So here's my questions:<br><br>A capacitor basically stores energy via an electric field, which is created by charges accumulating on separated plates (generalizing here). The voltage across these plates is proportional to the amount of charge stored and so forth. As a battery discharges, the voltage remains relatively constant until it's nearly depleted. But because of how capacitors store energy, the loss of charge will result in a loss of voltage. So if I use super capacitors as a power source, is there any rule of thumb to predict how long the voltage will remain roughly around 3.3V? (I probably could work it out by hand, but this seems rather application dependent).<br><br>Also, do you recommend any current protection when using these caps? In my project, everything is primarily digital, so it'll only draw however much current is needed, but I'm a little concerned just based on how quickly capacitors can discharge versus a regulated power source.
<p>When salvaging components from circuit boards are all capacitors that look like the ones pictured at the top of this page super capacitors. If not how can I tell a super capacitor when I see one?</p>
<p>There is not much difference really between run of the mill electrolytic caps and supercaps. A rule of thumb is one farad and up, i.e. 1F. 100,000 uF is 0.1F</p><p>In all likelihood the caps you salvage are not supercaps but nevertheless useful components.</p>
<p>I want to use a super cap or several, to light a half dozen LEDS. I am going to charge the caps with small solar cells. My question is how many Farads do I need to keep the lights going for 5 or 6 hours. </p>
<p>If you don't do to the math you will have to experiment. The math involves knowing the current and voltage of your LEDs, the power of your solar panel, and of course capacitors discharge exponentially (not anything like a battery) so perhaps you should experiment with small devices first.</p>
<p>which size battery can i use for charging a 450 volts and 100uf(m) capcitor.</p><p>help me plz</p>
<p>Anything up to a 450 volt battery will charge your capacitor to the voltage of your battery, but only 100uf.</p>
<p><strong>Can I replace a 1000uf 6.3v for a 1000uf 10v capacitor ? please help me </strong></p>
<p>Yes you can.</p><p>Your circuit will only charge it to the voltage that it is supplied with though...</p><p>the 10V cap will only store max 6.3V that the origanal Cap would have stored.</p>
<p>I've looked at this circuit (balancing circuit show above) about 30 times now, and I really don't get a few things. First, assuming the circuit as drawn, how did Johnson come up with the two resistors that go along with the reference diodes? I've looked up the datasheet for those diodes, run the values through some calculators, and I get minimum shunt resistor values more like 900&Omega; instead of the 33k&Omega; he used. I'm assuming the high values go along with the 10k&Omega; resistor to drop the current for the comparator, but I can't get the number he used.</p><p>Next, do you really need three voltage references for this? Couldn't you use just the first one, since they all seem to be generating the same reference voltage? Clearly you need all three comparators/op amps, but the references are just there to set a lower value to compare to the voltage divider output for each comparison. (I'll be using 5.5v supercaps, and I have a 5v rail available - I can't see why I'd need the voltage references at all. Just tie the negative values into the 5v rail.)</p><p>Finally, given the low voltages and currents involved here, is there some reason he couldn't just choose a suitable zener diode to balance these supercaps? 2.4V 1W? Or if you're feeling risky, 2.7V 1W? A 2.7V zener should start to breakdown just below 2.7, right? With 300mA max current, it doesn't seem like you'd be risking your wattage limits. I'm thinking about 5.1V, 5W zeners for my circuit, and wondering if I really need the comparators and MOSFETs at all. (30V max, 500mA max, coming from a bike hub generator, so there won't be a big in-rush issue.) This is a terrific circuit for more serious stuff, but it seems like serious overkill for the circuit that's there.</p>
<p>hello sir, </p><p>we are working in a solar car project,our problm is:-</p><p>1.we have to ride the car with solar power without using batteries,for a 50-70(meters),the car weighs 250kg(max).</p><p>we r using 3 solar panels and we r getting approx. 470w from it.</p><p>is it possible to drive d car with that power.</p><p>if NO, for initial torque we r going to use super capacitor,is it possible.....</p><p>please give d super capacitor values,nor possible suggestions......</p><p>i will be very much thankfull to u .....................</p>
<p>hello sir, </p><p>we are working in a solar car project,our problm is:-</p><p>1.we have to ride the car with solar power without using batteries,for a 50-70(meters),the car weighs 250kg(max).</p><p>we r using 3 solar panels and we r getting approx. 470w from it.</p><p>is it possible to drive d car with that power.</p><p>if NO, for initial torque we r going to use super capacitor,is it possible.....</p><p>please give d super capacitor values,nor possible suggestions......</p><p>i will be very much thankfull to u .....................</p>
Hi sir good day!!<br>Sir we are now working with our project, and we have some problem regarding it. Our project is a solar panel and we can only produce 500mv with a current of 1mA. Will we be able to store enough voltage and current on a capacitor for our converter to work which have a minimum input of .9V and 100mA? What rating of capacitor is necessary if possible?<br><br>By the way sir thank you very much for you're instructables, it was helpful.
<p>Is it possible to charge a supercacitor to store energy beyond the voltage of the input source. For example if I hook up a 1.5V battery to the supercapacitor with a diode in between to prevent discharge can the supercapcitor drain the battery and store the charge from it to 2V? I have tried and it does not work. I am trying to use the supercacpitor to store energy and then use it for light an LED, but the input source I have goes to a max of 1V. What circuit should I be using/modifying. Any thoughts.</p>
<p>The supercapacitor voltage will only go as high as your input source. That is to say if you have a 1V input source you will only be able to charge the super cap up to 1V. You can use a boost converter to make your input source 2 V. For example, the MCP1640 allows you to set your output to the needed voltage using a couple of external resistors. Note that you will also need an inductor. </p>
<p>hi i want buy the super capacitor charger where can i get it thanks </p>
<p>Please care enough to go through this article and correct the misspellings, please. <br>It's hard to take the copy seriously when you write 'listening' as 'listing'. <br><br>Please, from now on, always have another human carefully proof read your copy. <br>You want us to take you seriously, right? Care enough to do it right. <br>Thanks.</p>
<p>A few spelling mistakes? Really? This instructable may not be perfect, but it has been helpful to many. Instructables liked it enough to feature it. Take me seriously or don't. I didn't ask for you to read it. I didn't ask for your approval. I spent many, many hours of my own time on this, so please, if you have nothing kind to offer, then please don't post on my instructables.</p>
<p>These videos are in one word &quot;AWESOME&quot;</p>
<p>to sustain a circuit requiring 300ma almost for 10 hrs, how much charge should a supercapacitor store.</p>
<p>i meant 5v 300ma.</p>
<p>Errata, example 2: The total capacitance in series is: CT=1/(1/C1+1/C2), so then, CT=1/(1/200 + 1/1000) = 166.66f , Not 1200f.</p>
<p>can I use a 400V capacitor in a 5volt circuit using a 5 volt zener to limit to voltage going into the capacitor if i can how will it effect the cap thanks</p>
Conductor will go red??? Then discharging takes how much time??? And isn't it supposed to make a BIG spark, I do this with my 450v 220uF cap..
I salvage components from my retired electronic devices. How can I identify any of the capacitors are &quot;super capacitors&quot;?
<p>Very high farads in a (relatively) small package. you probably wont find them. The big ones are mostly used as regenerative breaking buffers in large vehicles, sometimes the little ones are used as backup power sources for small ICs (they keep the clock from resetting if the device looses power)</p>
<p>Update: there is now a mosfet that has been engineered just to balance Super Capacitors. They are made by Advanced Linear Devices... google SAB mosfet to learn more. I just ordered a couple from digikey to try out on my bank...</p>
This message is for Rahul Nema. I am trying to do something similar but Engineering guy said it is was not going to be easy and very costly. His advice was to buy batteries. NOW with the advent to the super capacitor out for some time, please let me know what you came up with .. if you did. In my case I have only 1.4kw solar and I dont want lead batteries to gas up the area. You can contact me at my mail at bent1615 at gmail if you like. hope to hear from you. TIA <br>Ben
Hi. <br>For the queries about using supercaps as replacements for batteries, the maths for capacitors to current is pretty simple. You only need two formulae: <br>(1) CV=Q where C=capacity in farads, V = voltage, Q= charge on capacitor in Coulombs. <br> <br>(2) Q=It where I=current in Amps, t= time in seconds. <br> <br>(3) From (1) and (2) we get CV=It <br> <br>So, if you have a 1F supercap charged to 5v and take 1amp from it, it will last for 5 seconds. <br> <br>A 100F supercap at 10v will supply 5A for 100x10/5 secs= 200 seconds or 3 mins roughly. <br> <br>Compare this to a AA 1.25v 2Ah rechargeable. By multiplying the voltage by the current by the time in seconds we can find out how many Coulombs this is equivalent to. This will provide a total of 1.25x2x3600 Coulombs of charge = 9000 Coulombs. <br> <br>Using equation (1) (C=Q/V) we can see that this is equivalent to a 9000/1.25=7200F supercap. In fact, because of the maths, you can work out the battery equivalent in supercaps by multiplying the battery Ah by 3600 if the supercap and battery are used at the same voltage. <br> <br>A standard 12v 40Ah lead acid battery is equivalent to a 144,000F 12v supercap. <br> <br>As you can see, there are significant cost issues in using supercaps as replacements for high capacity uses when replacing even small batteries, although they do obviously at this moment in time have their uses for low power/short surges and quick charge situations. There are also issues regarding supercap voltage. This will droop linearly with the amount of charge taken, unlike a battery which stays pretty stable until near the end of its charge. This means the supercaps will require some sort of voltage stabilisation circuitry in addition to the supercaps. <br> <br>They will develop over time though, as all new technology does and there is huge potential in the future for high capacity battery replacement but it's probably still quite a way off. <br> <br>I hope this helps.
Sir,<br> I am working on your project.<br> But I cannot find LMP2231, MPV30UN, LM385 in my local market. Problem is I am from bangladesh and its difficult to bring those parts from USA.<br> So, if you can give any alternative of those parts.
Would you expect a damaged 3000F ultracap to be reliable still if they have 60-80% of their original capacity?
I'm thinking about setting up a minimal solar power system to provide power to a very tiny off-grid house and I'm trying to figure out if there might be a way to make it work without using a battery bank.&nbsp; I realize that this setup would not provide any power after the sun goes down but the fridge I list below is designed to hold it's coldness through the night.&nbsp; My idea is to hook about 200 watts of solar panel(s) to a super capacitor and then run a super efficient chest fridge and a washing machine directly off the solar panels through the capacitor. The idea is that the capacitor would help to manage the start up power surge that the electric motors cause and would also smooth out and regulate the power. The fridge would be something like the <a href="http://www.sunshineworks.com/sundanzer-bfr105-solar-refrigerator.htm" rel="nofollow">SunDanzer BFR105</a>.&nbsp; I would hope to use an energy efficient washing machine too but I'm not sure what the amperage draw would be.&nbsp; There is one web site <a href="http://www.los-gatos.ca.us/davidbu/pedgen/washing_machine.html" rel="nofollow">here </a>that gives some idea of the typical&nbsp; power draw during various washing cycles.<br> <br> Some questions I have are:<br> <br> 1.) Would a 20 Farad capacitor like <a href="http://www.amazon.com/Audio-Cap20-Farad-Capacitor-Chrome/dp/B001TBO3OS/ref=sr_1_3?ie=UTF8&qid=1362364406&sr=8-3&keywords=super+capacitor" rel="nofollow">this </a>be suitable for this application or would I need a larger size?<br> <br> 2.) Am I understanding correctly that a 250 watt solar panel like <a href="http://www.grapesolar.com/index.php/products/modulesandkits/gs-s-250-fab5" rel="nofollow">this&nbsp; </a>with a Maximum Power Point Voltage Vmpp of 30.7 V would put out a voltage that is too high for the capacitor but that two 100 watt panels like <a href="http://www.grapesolar.com/index.php/products/modulesandkits/gs-s-100-ts/" rel="nofollow">this&nbsp; </a>in parallel with a Voltage at Maximum Power Point Vmpp of 17.7 would work correctly?<br> <br> 3.) Do you have any idea what would happen if the washing machine attempts to draw more watts for too long a period than are available?&nbsp; On the pedal power web site it shows that the washing machine draws up to 820 watts at certain times during spin cycles but at other times the draw is much lower.&nbsp; If not enough watts would be available would the machine simply run more slowly?&nbsp; It seems that the wash cycle would be ok but that the spin cycle might quickly run the capacitor down.<br> <br> Thanks for any advice you might have about this idea.
hi guys, <br>this is rahul nema. I am doing my thesis work in which i am making a MATLAB model for Super Capacitor Energy Storage system actually by using this Super Capacitor I am maintaining frequency constant of a 100 KW biomass gasification plant. guys I am very confuse about the rating of the Super Capacitor I mean yet I have not decided what should be the capacity of my Super Capacitor energy storage device. 90 KW load is connected to the 125KVA (100 KW) generator. so please guide me how I proceed in my work.. <br>Thanks.. <br>If you want any other inquiry so plz tell me..
Isn't charging a capacitor with 1A dangerous for you if you take a shock (with the power supply)?
Hi there <br>No, it is not. At low voltages, if you're charging at high amperage, your only worry would be to burn yourself on the charging conductor. However, when charging at say 5-7v at 1A, it won't get that hot =) You're never going to have to worry about a shock. Remember, your body resistance is in the megaohms, so even if you touch the charging conductor and the ground, you're only going to have 5-7v at uA flowing through you, which is not dangerous at all.
Amazing instructable! <br><br>Easy to understand and the best guide about super capacitors I know!
i have accidentally melted a wrench with a full bank of golf cart batteries... oops... o.O i have also designed a fire started with a thing i call zapbox. i has 2 9 volt batteries to charge a few capacitors and then go directly across a thin wire wrapped around the head of a match. perfect for starting fire from a distance!
Brilliant ! Thanks for sharing. It has made my mind boggle. That is, what would be the global impact if all cars were fitted with caps instead of batteries. No lead or acid in the environment and light a weight resulting in a further MPG? Is this a dream or feasible?
Un lien est une alternative, il vous laisse libre, vous pouvez l'utiliser ou non. D&egrave;s lors que ce n'est pas une fen&ecirc;tre popup qui s'ouvre automatiquement, il ne provoque aucune g&egrave;ne. Apr&egrave;s tout lorsque vous effectuez des recherches internet vous choisissez ce sur quoi cliquer.<br>La libert&eacute; des uns s'arr&ecirc;te &agrave; celle des autres et proposer n'est pas imposer.<br><br>A link is an alternative, it leaves you free, you can use it or not. Since this is not a popup window that opens automatically, it does not cause gene. After all when you search online you choosing what to click.<br>Freedom of some stops at the other and offer not to impose.
Stupid Me needs a question answered about bipolar caps. A audio circuit calls for a 4.7uf bi polar cap. Is there any difference in types of caps as I have two Bipolar crossover caps. Are all bipolar caps made the same or what gives as I am new to electronics.
Caps are made with several different materials giving different properties. <br><br>Check the voltage rating needed.<br><br>It would have helped if you stated what types you have................

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