Category Archives: Capacitors

Building a UPS with Raspberry Pi and Supercapacitors

It is always a dilemma when integrating a Raspberry Pi (RBPi) Single Board Computer into a project that works on the mains voltage and the RBPi has to turn it on or off. The difficulty is in deciding whether to power the RBPi separately or maybe power it from a UPS.

Lutz Lisseck solved the problem in an ingenious way. He was looking for a way to shut down his RBPi gracefully, after it had turned off his ambient-lamp. Since the lamp operated directly from the mains and Lutz wanted to turn it on/off from the mains power switch, he would normally have two choices. He could either use a mains wall adapter to power his RBPi or use a battery pack as a traditional UPS. He decided he did not like either, and instead opted for a third alternative, building a UPS with supercapacitors.

Lutz used two 50F supercapacitors to make his UPS. When the lamp was on, the capacitors stored enough charge to outlast the RBPi. When the SBC cuts the power, a GPIO pin senses the loss and informs the RBPi to begin its shutdown sequence. The RBPi takes about 30 seconds to shut down, and the capacitors happily power it for the time. Supercapacitors are usually rated at 2.7V; therefore, Lutz had to put them in series for the RBPi to get 5V. An alternative would be to place the capacitors in parallel and use a step-up converter to jack up the voltage. An upside to this is the capacitors will supply the RBPi for a longer time.

Since the project was a very simple one, there are some shortcomings in using the RBPi this way. First, the capacity is just about enough to shut down the RBPi in 30 seconds. However, when switched on, the capacitors take time to charge and the RBPi has to wait for about 10 seconds, before it gets adequate voltage to boot. Another drawback is that although the RBPi has only 30 seconds to shutdown, the capacitors discharge very slowly, and the system has to remain unplugged for about 10 minutes after shutdown, before it will boot up again. For this ambient-lamp project, Lutz does not consider that as a handicap.

Using supercapacitors over batteries has some advantages as well. The capacitors have a lifetime that far surpasses that of batteries. For example, you could charge and discharge supercapacitors completely several 100,000 times. Moreover, supercapacitors can be charged and discharged at rates that are not possible with a battery. A completely discharged supercapacitor can be fully charged up in just 2 minutes.

Therefore, with the supercapacitors in place, you do not need to worry about improper shutdown when the mains supply collapses. A GPIO pin on the RBPi senses when the mains voltage has been removed and the RBPi immediately begins a shutdown sequence. Whether using the supercapacitors in series or in parallel, a low value resistor (0.5-2.0 Ohms) must be placed in series with the batteries to limit the inrush current at startup. As the resistor can get hot, preferably a high wattage type should be used.

Building a UPS with Raspberry Pi and Supercapacitors

It is always a dilemma when integrating a Raspberry Pi (RBPi) Single Board Computer into a project that works on the mains voltage and the RBPi has to turn it on or off. The difficulty is in deciding whether to power the RBPi separately or maybe power it from a UPS.

Lutz Lisseck solved the problem in an ingenious way. He was looking for a way to shut down his RBPi gracefully, after it had turned off his ambient-lamp. Since the lamp operated directly from the mains and Lutz wanted to turn it on/off from the mains power switch, he would normally have two choices. He could either use a mains wall adapter to power his RBPi or use a battery pack as a traditional UPS. He decided he did not like either, and instead opted for a third alternative, building a UPS with supercapacitors.

Lutz used two 50F supercapacitors to make his UPS. When the lamp was on, the capacitors stored enough charge to outlast the RBPi. When the SBC cuts the power, a GPIO pin senses the loss and informs the RBPi to begin its shutdown sequence. The RBPi takes about 30 seconds to shut down, and the capacitors happily power it for the time. Supercapacitors are usually rated at 2.7V; therefore, Lutz had to put them in series for the RBPi to get 5V. An alternative would be to place the capacitors in parallel and use a step-up converter to jack up the voltage. An upside to this is the capacitors will supply the RBPi for a longer time.

Since the project was a very simple one, there are some shortcomings in using the RBPi this way. First, the capacity is just about enough to shut down the RBPi in 30 seconds. However, when switched on, the capacitors take time to charge and the RBPi has to wait for about 10 seconds, before it gets adequate voltage to boot. Another drawback is that although the RBPi has only 30 seconds to shutdown, the capacitors discharge very slowly, and the system has to remain unplugged for about 10 minutes after shutdown, before it will boot up again. For this ambient-lamp project, Lutz does not consider that as a handicap.

Using supercapacitors over batteries has some advantages as well. The capacitors have a lifetime that far surpasses that of batteries. For example, you could charge and discharge supercapacitors completely several 100,000 times. Moreover, supercapacitors can be charged and discharged at rates that are not possible with a battery. A completely discharged supercapacitor can be fully charged up in just 2 minutes.

Therefore, with the supercapacitors in place, you do not need to worry about improper shutdown when the mains supply collapses. A GPIO pin on the RBPi senses when the mains voltage has been removed and the RBPi immediately begins a shutdown sequence. Whether using the supercapacitors in series or in parallel, a low value resistor (0.5-2.0 Ohms) must be placed in series with the batteries to limit the inrush current at startup. As the resistor can get hot, preferably a high wattage type should be used.

More Italfarad, Ducati & Gentex Motor Start & Run Capacitors in stock!

more motor start capacitors in stock!

You’ve been asking for them – now we have them. We’ve added more values to our motor start and motor run category including some from Italfarad, Ducati and Gentex.

Check out our full selection at https://www.westfloridacomponents.com/MotorStart-RunCapacitors.html.

Need a different value? Ask us, we might be able to get them for you!

What is a capacitor used for?

Just as a bucket holds water, a capacitor holds charge. In fact, the world’s first capacitor was in the shape of a jar and was aptly named the Leyden jar. However, the latest capacitors do not look anywhere close to a jar. In its simplest form, a capacitor has two conductive plates separated by a dielectric. This helps maintain an electric charge between its plates. Depending on the type, different materials are used for the dielectric, such as plastic, paper, air, tantalum, polyester, ceramic, etc. The main purpose of the dielectric is to prevent the plates from touching each other.

The Leyden jar was invented in the 18th century, at the Netherlands University. It was a glass jar coated with metal on both the inside as well as the outside, with the glass effectively acting as the dielectric. The jar was topped off with a lid. A hole on the lid had a metal rod passing through it, with its other end connected to the inner coat of metal. The exposed end of the rod culminated in a metal ball. The metal ball and rod was used to charge the inner electrode of the jar electrically. Experiments in electricity used the Leyden jar for hundreds of years.

A capacitor can be used in a number of different ways, such as for storing digital data and analog signals. The telecommunication equipment industry uses variable capacitors to adjust the frequency and tuning of their communications equipment. You can measure a capacitor in terms of the voltage difference between its plates, as the two plates hold identical but opposite charge. However, unlike the battery, a capacitor does not generate electrons, and therefore, there is no current flow if the two plates are electrically connected. The electrically connected plates rearrange the charge between them, effectively neutralizing each other.

A naturally occurring phenomenon, lightning, works very similar to a capacitor. The cloud is one of the plates and the earth forms the other. Charge slowly builds-up between the cloud and the earth. When this creates more voltage than the air (the dielectric) can bear, the insulation breakdown causes a flow of charges between the two plates in the form of a bolt of lightning.

As there is only a dielectric between the two plates, a capacitor will block direct current but will allow alternating current to flow within its design parameters. If you hook up a capacitor across the terminals of a battery, there will not be any current flow after the capacitor has charged. However, alternating current or AC signal will flow through, impeded only by the reactance of the capacitor, which depends on the frequency of the signal. As the alternating current fluctuates, it causes the capacitor to charge and discharge, making it appear as if a current is flowing.

Capacitors can dump their charge at high speed, unlike batteries. That makes capacitors eminently suitable for generating a flash for photography. This technique is also used in big lasers to get very bright and instantaneous flashes. Eliminating ripples is another feather in the capacitor’s cap. The capacitor is a good candidate for evening out the voltage by filling in the troughs and absorbing the crests.

Variation of Capacitance of Ceramic Capacitors with Voltage and Temperature

The ceramic capacitors that you work with in the lab have two or more alternating layers of a metal acting as the electrodes and a ceramic acting as the dielectric. The capacitance measured in farad represents the charge stored in a capacitor at a particular applied voltage. The quantity should be a constant for a particular capacitor at all values of applied voltages and temperatures.

Capacitor Categories

While working with Class I capacitors, you may find that their capacitances do not deviate from the expected values. However, Class II and Class III capacitors do show a marked deviation from the rated values. These capacitors have greater volumetric efficiencies, however. This means that they offer higher capacitances compared to the volume occupied by the capacitors.

Identifying Codes

An alphanumeric code of three characters designates the type of a class II capacitor. The first and second characters of the code indicate the lower and upper limits of temperature and the third character specifies the change of capacitance within the range.

Take the case of X7R, which is a popular Class II capacitor. The letter X indicates a lower limit of temperature of -55°C and the number 7 indicates an upper limit of +125°C. The third character R points to a change in the actual capacitance by +/- 15% from the rated value while the device is working within the temperature range defined above.

Deviation of Capacitances

In other words, you can expect that an X7R capacitor of a rated value of 4.7 microfarad might show a capacitance of 3.9 microfarad, while working under these temperature limits. However, it is a common occurrence to find that capacitors in certain circuits show a much more remarkable drop from their rated values. An X7R capacitor can exhibit a drop of 20%. Certain other Class II capacitors may show a drop as significant as 80% of their rated values of capacitances.

The real fact is that the rated capacitance value of a capacitor holds for a particular value of the applied voltage, also called the DC bias voltage. If the bias voltage is different from the specified value, the capacitor will offer a capacitance that is different from the rated value.

For instance, if you choose a capacitor of 4.7 microfarad designed to operate at 16 V, it may offer a capacitance as low as 1.5 microfarad while working at 12 V.

The code used to identify the capacitors does not indicate the exact variation of capacitance with the applied DC bias voltage. However, it is a known fact that Class II capacitors designated by the letter X are the most stable. The capacitors designated by the letter Y are less stable under adverse environmental conditions while the Z capacitors are the least stable.

Material Used

To understand the problem, you need to study the data sheet for capacitors, which indicates the variation of capacitance with the applied bias voltage. The data sheet illustrates another interesting fact regarding capacitor sizes. A larger capacitor offers a greater capacitance at a particular DC bias voltage than a smaller one identified by the same alphanumeric code. Hence, you can expect a better performance with a larger capacitor than with a smaller capacitor of the same code. A possible reason for the fact could be that manufacturers have to compromise on the material while making smaller capacitors of the same code.

How Professional Grade Capacitors Are Used In the Automotive Industry

The challenging conditions faced by automobiles have compelled component manufacturers in the automotive industry to come up with superior capacitors. Two of these advanced capacitors are professional grade capacitors of tantalum and niobium oxide.

A capacitor is comprised of two conducting plates separated by a dielectric (insulating) medium. One plate maintains a positive charge while the other maintains a negative charge.

Benefits of Professional Grade Tantalum Capacitors

A tantalum capacitor has a pellet of tantalum as the positive end separated from the negative conductor by a dielectric, which in this case is a thin layer of tantalum oxide formed on the tantalum pellet surface.

Professional grade variety of tantalum capacitors has several advantages over standard tantalum capacitors. Manufacturers adopt strict design specifications to construct the capacitors and use thicker and better dielectrics. In addition, the manufactures check the devices for high surge current and burn-in procedures.

The use of these capacitors results in a low failure rate of 0.5% in 1000 hours. In addition, the leakage current is almost 75% less than that in conventional tantalum capacitors. Manufacturers make professional grade capacitors available with low and standard equivalent series resistances (ESR). This makes these components suitable for several types of control circuits in automobiles.

The low ESR capacitors are particularly useful in airbag modules, engine control modules and power supply modules.

Functioning at High Temperatures

Automotive engineering requires placing electronic components close to sources of heat like engines, gearboxes, AC circuits and headlights. The temperatures in these regions may be in the region of 175°C. Since tantalum capacitors can function over a wide temperature range from -55°C to +175°C, they are suitable for use in these regions.

Niobium Capacitors

How The Automotive Industry Uses Capacitors

Before deciding on a tantalum or niobium oxide capacitor in a particular automotive circuit, the industry thinks about the nature of the circuit and the device using it. The first factor, which is the maximum voltage drop across the load in the circuit, determines the voltage rating of the capacitor. The second factor is the applied DC voltage. The applied voltage must be 50% of the rated voltage for the capacitors. This takes care of an unexpected surge in voltage. The third factor is the maximum value of the operating temperature. The capacitor selected must be able to withstand the temperature of the operating device.

A circuit operating under high temperature conditions (up to 125°C) can expect to see additional voltage surges. It is crucial that capacitors employed can endure these issues.

New radial electrolytic capacitor assortment available!

Radial Electrolytic Capacitor Assortment

Radial Electrolytic Capacitor Assortment

By popular request we’ve added an additional radial electrolytic capacitor assortment to our lineup of available products. Like our other capacitor kits, this assortment has a big range of capacitances and voltages supported. And like our other assortments, every value is individually bagged and labeled.

But here’s where this kit differs from our other previous kits – we are now able to provide a list of manufacturers and temperature ratings for this assortment so you can be sure that the capacitors in this assortment meet your needs. We’ve designed this assortment to be perfect for anyone’s workbench or ideal in a classroom setting.

Capacitor values range from 0.22uF 50V to 6800uF 10V. There are about 245 radial electrolytic capacitors included spanning 27 different values. Some of the included manufacturers are Taicon, Paccom, Sprague, NIC, Nippon, Marcon and Panasonic.

Box Capacitors – so many in one place!

We’ve been very busy expanding another category for you: Box Capacitors.  Now in stock and ready to ship are more than 60 different values of box capacitors. In general, box caps are constructed of polyester film or metallized polypropylene. Some of the more popular manufacturers are Wima, Mallory and Philips.

In addition, (and somewhat related), we’ve greatly expanded our suppression and safety capacitor category. Between both categories, there are almost 75 new products added this week alone! Look for quantity discount pricing on almost all of the capacitors.

And, as always, we do not require a minimum purchase and our first class mail shipping rates are still a very reasonable $3.50 for all US purchases up to $15.00.

Motor Start Capacitors vs Motor Run Capacitors

motor run capacitorWe are often asked about the difference between the two different types of motor capacitors: motor run and motor start. Here are the basic differences between the two:

Motor Start Capacitors
The primary purpose of a motor start capacitor is to briefly increase the motor starting torque as well as to allow a motor to be cycled on and off very quickly. It operates in the circuit by staying active long enough to allow the motor to be brought to 3/4 of it’s full capacity. It is removed at that point by a switch in the circuit. You will find that the voltage rating is often one of these four: 125VAC, 165VAC, 250VAC, and 330VAC.

Motor Run Capacitors
Motor run capacitors will then operate after the circuit is started. Using a motor run capacitor will run the motor with greater efficiency. Motor run capacitors are designed for continuous duty. They are energized while the motor is in operation. You will often find motor run capacitors with a voltage rating of 370VAC or 440VAC with a capacitance of 1.5uF – 100uF. Typically, the construction material is polypropylene film.

Operational information
Electric motors that are single phase require a capacitor for a second-phase winding. If you use the wrong motor run capacitor, the rotor may hesitate due to an uneven magnetic field. The hesitation may result in performance issues such as a noisy or overheated motor, increased energy consumption and general decreased performance.

Faulty motor capacitors
You can sometimes spot a faulty motor run capacitor by it’s swollen appearance – or it may have blown and become leaky. Of course, these capacitors should be carefully replaced. In addition to an outright capacitor failure, the capacitance may become reduced over time. Capacitors that are operating with a decreased capacitance may create performance issues. Again, these capacitors should be carefully replaced.

Tantalum Capacitor Industry Needs New Resources

Tantalum Capacitor

Tantalum Capacitor

As the demand for tantalum has recorded 5% growth every year, the supply of tantalite has decreased setting up the electronic components industry with a possible shortage.

Tantalite, which is the key component of tantalum used to make tantalum capacitors, is mined primarily in three countries: Australia, Mozambique and Canada. Companies in those countries reduced or suspended production as the economy tanked in 2008 and consumer spending fell.

Recently, most production of tantalum has been taking place in Brazil and Africa but with the previous production facilities not producing the tantalum, a shortage through 2012 is possible.

What does that mean to consumers and companies that need tantalum capacitors?

Increased demand will push prices higher on current stock….and if current supplies are depleted, a shortage like the one that occurred in 2000 may occur pushing up prices even further.

Tantalum capacitors have grown in popularity for many reasons. To start with, tantalum capacitors have a larger volumetric efficiency when compared  to other types of capacitors. To illustrate this point, a 10uF tantalum can be used in place of a 100uF aluminum capacitor.

In addition, tantalum capacitors are able to be inserted on circuit boards easily. When you couple this with the tantalum capacitor’s greater  power dissipation characteristics when looking at other capacitors in this size range, tantalum capacitors  can be inserted in small spaces. This makes them good candidates for tightly designed boards. You will often find tantalum capacitors used in laptops, computers, cellular phones, auto circuits and other similarly sized electronic devices.

Another outstanding characteristic of tantalum capacitors is their nearly unrivaled life span. The shelf life of tantalum capacitors is unparalleled when looking at other capacitor types such as those made from electrolytic material since the performance qualities stay intact over time and they should not lose capacitance like many other popular capacitors.