How to Safely Use Capacitors and Save Some Money
Posted by McCombs on 1st Dec 2022
Capacitors are a feature in almost all of the circuits used in the modern world. Along with inductors and resistors, capacitors are among the basic passive components that are foundational to the function of electronics.
More specifically, a capacitor is a device that has the ability to store energy in an electric field. Like batteries, capacitors can hold a charge, but unlike batteries they typically store a much smaller amount of energy at equal sizes. Despite this limitation, they are vital for the design of circuits.
Capacitors are made out of two metal plates (usually metals like aluminum or tantalum) separated by dielectric materials. Dielectric materials are insulating substances that can be polarized by an electric field, making them useful for capacitors, and include substances like glass, ceramic, paper, and a number of other materials.
Capacitance is the ratio of a capacitor’s total charge over its voltage, measured in farads. Capacitance is directly proportional to the net surface area of the capacitor’s two plates and the permittivity (ε) of the dielectric between the plates. The general rule of thumb is the smaller the distance between the plates in the capacitor, the greater the capacitance.
Under default conditions, metals typically have an equal balance of positively charged particles and negatively charged particles. In this state, it is considered electrically neutral. However, when a power source or battery is connected to the metal plates of a capacitor, things begin to change. A current will try to flow through the capacitor; in other words, the electrons from the plate on the positive lead side of the battery will begin to move toward the plate connected to the negative lead side of the battery. Because of the dielectric material between the plates of the capacitor, the electrons will not be able to pass through and will begin to build up on the plate.
Once a certain number of electrons have accumulated on the plate, the battery no longer has enough energy to continue pushing more electrons onto it. This happens because the electrons on the plate have the property of repelling further electrons that would be pushed onto the plate.
Once no further electrons can be pushed onto the plate and the current has ceased its flow, the capacitor is considered fully charged. The first plate at this point has a net negative charge, whereas the second plate has a net positive charge. This creates an electric field with an attractive force that stores the charge of the capacitor.
Capacitor Dielectric Working Principle
Let’s take a moment to examine how the dielectric can increase the capacitance of the capacitor. As mentioned briefly earlier, a dielectric contains molecules that are polar. Put simply, this means that the particles can change their directional orientation based on the charges on the two plates. In other words, the molecules can align themselves with the electric field such that they allow even more electrons to be attracted to the negative plate, and simultaneously repel more electrons away from the positive plate.
The result of all this is that once the capacitor is fully charged, it continues to hold its electric charge for a long time even if the battery is taken away. Thanks to this phenomenon, capacitors are a form of electrical storage.
If the two ends of a capacitor are shortened through a load, then a current will begin to flow through the load. In this situation, the electrons that have accumulated on the first plate will begin to move toward the second plate until balance is restored on both plates and the capacitor can be considered, once again, electrically neutral.
Decoupling capacitors, sometimes referred to as bypass capacitors, are a common application for capacitors. Often used along with integrated circuits, decoupling capacitors are typically placed between the power source and the ground of the integrated circuit.
The function of a decoupling capacitor is to filter any noise in the power supply, such as the voltage ripples that happen when the power supply drops voltage rapidly for a very brief period of time, or when the switch of a portion of a circuit causes fluctuations in the power supply. Decoupling capacitors help by acting as a temporary power supply at the moment when the voltage drop happens, thereby bypassing the main power supply.
AC to DC Converter
One of the biggest applications of capacitors is their use in DC adapters. Although they’re only a piece of the puzzle (converting the AC voltage into DC voltage is done with a diode rectifier), without the help of capacitors, DC adapters would not work at all.
The output of the rectifier is a waveform, so the capacitor charges while the output of the rectifier rises. On the other hand, while the output of the rectifier declines, the capacitor discharges and smooths the DC output in the process.
Signal filtering is yet another standard application of capacitors. Because of their very specific response times, they have the unique ability to block low frequency signals while still allowing higher frequencies to pass through unobstructed.
Signal filtering is a feature in radio receivers that allows them to tune out undesired frequencies. It’s also found in crossover circuits inside speakers, used to separate the low frequencies for the woofer from the higher frequencies for the tweeter.
Capacitors as Energy Storage
Capacitors can also be used for energy storage. Despite their significantly lower energy storage potential compared to batteries of the same size, they have several advantages that batteries do not. Chief among these advantages are the ability to deliver energy much faster than batteries and the longer lifespan of capacitors. As such, capacitors are much more suitable for applications that require a quick burst of energy, or where energy storage needs to function for a long period of time.
However, with recent advances, some believe that capacitors can surpass batteries for energy storage. According to Maria Guerra, “Advances in supercapacitors are delivering better-than-ever energy-storage options. In some cases, they can compete against more-popular batteries in a range of markets.”
Making a Super Capacitor Battery Pack
Although it’s hardly common knowledge, you can make a rechargeable super capacitor battery that is environmentally safe and can serve to charge household devices. This super capacitor can last for many years with less than $100 in circuitry, saving a great deal of money compared to batteries.
Looking for capacitors for your supercapacitor project? These might be helpful.
Better still, with the right charging method (i.e. solar, direct current, etc.) you can charge a device fully in a matter of minutes. This allows you to have a portable power supply that can charge cell phones, radios, earbuds, lights, and more – with numerous advantages over traditional portable batteries.
According to an Arrow.com article on the topic:
“Supercapacitors can endure many more cycles of charging and discharging than conventional rechargeable batteries.
Other advantages for supercapacitors include greater power density, a higher peak power delivery capability, smaller size and lower equivalent series resistance (ESR). Finally, supercapacitors have the capability to release their charge slowly, like conventional batteries.”
Making a super capacitor can also allow you to adjust the voltage much more easily than a commercial battery with a predetermined voltage that is set by the manufacturer.
What Exactly is a “Super Capacitor?”
This energy storage system uses super capacitors instead of a traditional battery. Super capacitors are quite similar to ordinary capacitors mentioned earlier in the article, but they have much greater power storage potential.
Capacitors – of both the super and ordinary variety – are judged by two primary power storage measurements. The first variable is maximum charging voltage (measured in volts), and the second is capacitance (measured in Farads, as explained earlier in this article). To oversimplify things slightly, capacitance can be thought of as a way to measure how much energy a given capacitor can store. For example, an ordinary audio coupling capacitor or power supply circuit capacitor generally has a capacitance in the neighborhood of 0.0001 Farads (F) or 1,000 Micro-Farads (mF); this is a relatively high capacitance compared to many other capacitor applications. The units can be a little confusing, but just keep Science Direct’s definitions in mind:
“A microfarad is one-millionth of a farad, the nanofarad is one-thousandth of microfarad, and the picofarad is one-millionth of a microfarad.”
A super capacitor, on the other hand, can have a capacitance of anywhere from 1 to 2,000 Farads or more (1,000,000 to 2,000,000,000 mF). As it turns out, the “super” in “super capacitor” really isn’t an exaggeration. In fact, capacitors of that high efficacy make an excellent alternative to traditional commercial batteries.
Is It Right For Me?
If you are considering replacing your batteries with a super capacitor, it is important to consider the pros and cons of such a decision. If you are making your own, take special note of the safety considerations and be sure to weigh whether you can operate it without adding any danger compared to a traditional commercial battery.
- Superior Lifespan and Cycle Duration.
Super capacitors can withstand the cycle of charging and discharging more than 500,000-1,000,000 times – as long as you don't charge them at a higher voltage than their limit-rating or reverse the charge polarity.
- No Battery Memory Loss.
When you charge a traditional nickel battery without fully draining its charge – especially if you end up leaving it in the charger – the overcharging can deplete the battery’s ability to hold a charge (the “battery memory”) and it will eventually die. The super capacitor will STOP accepting any energy once it is full.
- Superior ESR and Charging Speed.
The internal resistance - also known as the equivalent series resistance, or ESR for short – is extremely low in a super capacitor that is well designed and constructed with the right materials. Typically, the equivalent series resistance of a super capacitor measures at 0.01 Ohms, or even lower. For a comparison point of reference, a typical commercial battery has an equivalent series resistance ranging anywhere from 0.20 Ohms to as low as 0.02 Ohms for highly efficient designs. This is important because resistance is a key factor in the speed at which a power storage unit like a capacitor or battery can be charged. Essentially, this means that you can charge your super capacitor in a matter of mere seconds; in most circumstances, the only limitation is how heavy duty your power supplies are. Compared to a good super capacitor, ordinary rechargeable batteries will take much longer to charge fully and will not be able to discharge as quickly.
- Longer Shelf Life.
Rechargeable batteries have a limited lifespan, even if they aren’t used in a manner that reduce their battery memory. If you leave a battery charged and unused sitting in a back shelf in your garage long enough, it will be dead when you try to use it. This is not the case with the super capacitor. Although they may suffer minor losses in capacitance and slight increases in their ESR, the shelf life of an average super capacitor is several times longer than that of a battery. If you need further proof of this fact, many super capacitor manufacturers offer warranties and service life guarantees lasting longer than a decade for their products; even some “economy” brands boast an expected service life of 10 years covered by warranty, with 15 to 60+ year lifespans under ideal conditions. In fact, technical guides state that unlike batteries, [super] capacitors do not exhibit a true end of life and that its life is predominately affected by voltage and temperature. Typically, on data sheets, the end of life is determined with the capacitance dropping by 30% and the internal resistance (ESR) is doubling, although in most applications the end of life will be when the performance of the [super] capacitors falls below the application requirements.
- Zero Toxic Greenhouse Gas Emissions.
Lithium-ion batteries and other rechargeable batteries release gasses that are dangerous to both the people around them and the planet at large. These gasses include the greenhouse gas carbon dioxide (CO2), the flammable and highly toxic gas carbon monoxide (CO), and dangerously explosive hydrogen (H2) gas. All three gases are harmful to the environment; according to NASA, carbon monoxide “contributes to the formation of tropospheric ozone, another air pollutant with unhealthy effects” and “affects the abundance of greenhouse gases such as methane and carbon dioxide,” and the Environmental Defense Fund states that hydrogen gas has a relative global warming impact that is “100X more potent than CO2 emissions over a 10-year period.” Due to the risk of explosion and poisoning from the gases that batteries emit, their use often requires additional ventilation for safety purposes (for a good example and practical tips, It Still Runs offers a step-by-step “safe indoor charging” guide that insists on precautions like extra ventilation and safety goggles); the battery gas emission problem is serious enough that it warrants federal regulation by the Occupational Safety and Health Administration (OSHA). Super capacitors have no such risks. They can be charged and stored indoors with no danger of gases harming you, your property, or your family – and they’re certainly better for the planet!
- Less Explosive Risk.
It’s not just gases that can explode with batteries. As far too many DIY electricians can attest, a direct short circuit can cause batteries to overheat, leak, and potentially explode. This can cause injury or fires, but these worries are non-existent with a super capacitor – they do not explode in the event of a direct short. However, it is important to consider that a direct short will cause the super capacitor to heat up drastically, and this can burn the user if they aren’t careful.
Which segways perfectly into the potential disadvantages of super capacitors.
- Bulky Size.
Super capacitors are much larger than batteries of equivalent energy storage capabilities. For example, if you were to build a super capacitor that was large enough to completely replace your car battery, it would potentially be 10 times bigger – and therefore completely useless for your car! The fact is, super capacitors have plenty of energy storage capability, but they do need to be properly banked in a series (or parallel) to match up the energy storage levels that ordinary batteries offer. According to EE Power’s knowledge hub entry on super capacitors, the physical volume isn’t the only bulk issue: “One disadvantage [of super capacitors] is a relatively low specific energy. The specific energy is a measure of total amount of energy stored in the device divided by its weight. While Li-ion batteries commonly used in cell phones have a specific energy of 100 to 200 Watt-hours per kilogram, super capacitors may only store typically 5 Watt-hours per kilogram. This means that a supercapacitor that has the same capacity (not capacitance) as a regular battery would weigh up to 40 times as much. The specific energy is not to be confused with the specific power, which is a measure of maximum output power of a device per weight.”
- Low Max Voltage.
In comparison to most powerful batteries, super capacitors typically have very low maximum voltage ratings. As a result, it is necessary to exercise great caution to avoid overcharging in order to avoid ruining the super capacitor permanently. Of course, the limited voltage rating would make them largely useless, so the standard workaround to this problem is placing several super capacitors in a series. Each addition in the series has the effect of doubling the voltage. The drawback to this solution, though, is that you lose capacitance with each addition to the series as well. This article covers the formula for series and parallel banking further down, so be sure to read through that section if you plan on capacitor banking.
- Burn Risk.
The low voltage rating of super capacitors has one silver lining: you don’t need to worry about shocking yourself. However, despite being able to rest easy when it comes to getting shocked, burns are a legitimate risk as we previously mentioned. With a full charge, a direct short circuit can make a super capacitor (or series of super capacitors in a power bank) heat up very rapidly to very high temperatures. If you make contact before it cools down sufficiently, there is risk of seriously burning yourself.
In some cases, super capacitors can be more expensive than batteries. The cost difference varies widely depending on what brands and models of super capacitor and battery you choose to compare. You can potentially save some money by shopping around or making your own at home (if you have the appropriate tools and understanding of safety protocols). Although the advantages of super capacitors can save you money in the long-term compared to an equivalent commercial battery, so consider all you options before making a purchase.
The DIY Power Bank
Now that you have a good grasp on super capacitors, how they work, their advantages and disadvantages as energy storage devices over traditional commercial batteries, and some basic safety tips, it’s time to consider how an effective power bank can be made from one or more super capacitors right in your own home. A power bank, put simply, is a portable energy storage device that utilizes specialized circuitry to control the power that goes in and out.
Many people nowadays carry power banks sold as “backup phone batteries” or “external USB charging ports,” which are the same as this DIY super capacitor power bank – with one big difference: they run on lithium-ion batteries, and carry along with that all the disadvantages and limitations of a lithium-ion battery. For example, lithium-ion power banks require careful maintenance; you must be diligent in avoiding any overcharging or undercharging, or else suffer the consequences of the power bank’s maximum charge slowly dwindling and eventually giving out completely.
To live free from the headache of caring for a fickle commercial power bank, here is a step-by-step guide for creating a power bank that runs on super capacitors – and boasts a longer lifespan, significantly faster charging speeds, and much easier maintenance requirements.
Essentially, you are creating a fairly straightforward circuit. It runs on a parallel configuration super capacitor circuit that, when charged, results in a capacitive voltage that is greater than the sum of an individual capacitor’s voltage. That voltage goes into a voltage regulator, making a DC output with a constant voltage and constant current. That regulator’s output gets fed through an inductor that regulates the current, and then it proceeds on to the USB connector’s +ve terminal.
The Hardware You’ll Need
Just like in cooking, you can’t make a good super capacitor without the right ingredients. There’s a few less common items on the list, but none of these things should be too difficult to find with a little effort. Here are the parts you’ll need:
- 1 x Veroboard. Ordinary, standard stripeboard should do the trick – just make sure it’s big enough to hold all the parts together.
- 1 x Inductor (50 nH). Any fitting inductor component will work, as long as it has a 50 nano-Henry inductance rating.
- 9 x Polar Capacitors (4700uF/10V). These might take a little hunting to locate.
- 1 x Soldering Iron (45W-65W). Most common soldering irons should be in the suitable wattage range, or at least it should be easy to find one that is. It might be wiser to start at the lower wattage, though – according to American Beauty Tools, “if you are an average user, try to go for no more than 45 watts. If you are a solderer that has a bit more experience, then you can go for about 60 watts.”
- 1 x Voltage Regulator IC (Type LM7805). These might be the hardest item to find, but they can still be purchased in 10-piece packages quite cheaply on sites like eBay or found at electronics outlets.
- 1 x USB (Type-A) Connector Port. These are so common nowadays that may you have some lying around in your junk drawer. If not, you can find them anywhere hardware and electronics are sold for just a few dollars.
- 1 x USB Data Cable. These are so common that you almost certainly have a spare in your home, potentially even lying unused within spitting distance of you as you read this!
- Sufficient Soldering Wire with Flux. This follows from the soldering iron listed above, obviously.
- Plenty of Connecting Wires. Your requirements will vary quite a bit here, but this is something you’ll probably have on hand if you do any electrical DIY work or perform any of your own maintenance on electronics.
- A 220 Volt Electrical Outlet.
Lastly, of course, you will need the item that you wish to charge. This can be anything that connects to the appropriate USB charger, from wireless earbuds to a pacemaker. However, a smartphone is probably the most practical and likely candidate, so let’s assume that charging a smartphone is the goal moving forward.
The Nitty Gritty Details
Get your work station set up and make sure your soldering iron and wire are close at hand. Have a look through the LM7805 product and data sheet for a comprehensive breakdown of its specifications, such as dimension features and pinout. Make sure everything matches up neat and tidy, and get ready to solder.
Begin by soldering all the +ve terminals of the 4700uF capacitors to each other. Then, solder all the -ve terminals of the capacitors to each other the same way, in a parallel configuration.
Next, solder the super capacitor config’s positive terminal to the Vin of the LM7805 Voltage Regulator, and solder the -ve terminal to the Ground of the IC. This takes some dexterity, so be steady with your hands. Once this is complete, solder a 50nH inductor IC’s output.
After the inductor has been soldered to the IC output, solder the inductor output to Pin 1 (Vcc) of the USB Port and the super capacitor’s -ve terminal with the GND pin. Using the 220V electrical outlet, charge the super capacitor for approximately 2 seconds, and then plug your smartphone in via the USB connector cable. This is a test of the circuit, and if everything is hooked up correctly it should work like a charm.
Although the resulting tangle of Veroboard and electrical components may be somewhat unsightly, you now have a more effective and easily charged power bank. Using these basic components and their counterparts, you can expand on the lessons learned from this project to use super capacitors for all sorts of applications.
Replacing Blown Capacitors
For some folks, it’s time to buy a whole new device at the first sign of trouble. But for others, the challenge of determining what causes failure in our electronics and trying to fix it can be an experience that is educational, fun, and rewarding (in terms of both knowledge and the money saved). Checking for blown capacitors is a quick, easy way to do this, and it can prevent wasting hundreds of dollars in a total replacement for expensive electronics.
Before all else, know the symptoms of a blown capacitor:
- The device simply won't turn on.
- The device won't return from standby mode.
- The device turns on and off intermittently.
- The screen on the device is flickering or distorted.
- There are lines across the screen of the device.
Once you suspect a blown capacitor, all it takes to investigate further is a few common tools, a little time and effort, and basic knowledge of what to do.
Here’s how to proceed:
Power the device off completely and (if plugged in) unplug it. Wait a moment, and then open the case or covering to gain access to the circuit board within. If the device is particularly well-armored – and you’re confident you can put it back together after opening it up – you may want to check an online manual or YouTube video on how to properly get it open.
Inspect closely under good lighting and check the electrolytic capacitors. A blown capacitor is often quite obviously broken – it may be corroded horrendously, leaking rust-colored goo, or have the leads completely severed. Sometimes, though, it’s less clear. Check carefully to see if the top of the capacitor is bent outward slightly in a convex shape, as opposed to the inward indentation or flat alignment of a functional capacitor. A capacitor is like a bottle with an airtight seal: when the seal is unbroken the bottle cap is flat, but when it’s open the cap pops up. A popped-up shape is a sure sign of a blown capacitor.
Note the original capacitor’s polarity, writing down the exact specs needed for a replacement. You’re typically looking for either the capacitance and voltage/temperature ratings, often written on the part itself, or the part’s model number that will allow you to find the same model or an equivalent.
To remove the old capacitor, apply a hot soldering iron to the solder joint on the back of the circuit board, holding onto the capacitor itself with your other hand. Once the joint begins to melt, the top will fall through the hole in the board, allowing you to pull that side's wire lead out. Repeat on the other side. This might take a few tries, but usually you can get it with some focus and dexterity.
Once you have the new capacitor, trim the leads evenly to sit at the same height as the original. Place the leads at the holes where the old capacitor was, keeping in mind the correct polarity. As before, press the tip of the soldering iron onto the joint on the back circuit board. When the tip falls into the hole, press the wire lead and remove the iron. The old solder joint will solidify and hold it secure. Repeat with the other side, and voila! Put the circuit board back into the case and test power output – if the capacitor you replaced was the culprit, everything should be working now. So, simply place the circuit board back into its case and test the power and output. The electronics should work now!