The typical temperature range for aluminum electrolytic capacitors is –40 °C to 85 °C or 105 °C. Capacitance varies about +5% –40% over the range with the capacitance loss all at cold temperatures. Capacitors rated –55 °C generally only have –10 % to –20 % capacitance loss at –40 °C. Cold temperature performance for rated voltages of 300 V and higher is often worse, and temperature performance varies by manufacturer.
Aluminum Electrolytic Capacitors capacitor element is wound on a winding machine with spindles for one-to-four separator papers, the anode foil, another set of one-to-four separator papers and the cathode foil. These are wound into a cylinder and wrapped with a strip of pressure-sensitive tape to prevent unwinding. The separators prevent the foils from touching and shorting, and the separators later hold the reservoir of electrolyte.
Before or during winding aluminum tabs are attached to the foils for later connection to the capacitor terminals. The best method is by cold-welding of the tabs to the foils with tab locations microprocessor controlled during winding so that the capacitor element’s inductance can be less than 2 nH. The older method of attachment is by staking, a process of punching the tab through the foil and folding down the punched metal. Cold welding reduces short-circuit failures and performs better in high-ripple current and discharge applications in which the individual stakes may fail from high current like buttons popping off one at a time from a fat-man’s vest.
Aluminum Electrolytic Capacitor are connected in series, back-to-back with the positive terminals or the negative terminals connected, the resulting single capacitor is a non-polar capacitor with half the capacitance. The two capacitors rectify the applied voltage and act as if they had been bypassed by diodes. When voltage is applied, the correct-polarity capacitor gets the full voltage. In non-polar aluminum electrolytic capacitors and motor-start aluminum electrolytic capacitors a second anode foil substitutes for the cathode foil to achieve a non-polar capacitor in a single case.
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An Integrated Circuit [IC] is normally decoupled using one bypass capacitor from 0.01uf to 0.1uf.Using the graph below, the 0.1uf response would result in the first dip at f1 followed by the dotted single line.
Placing a 0.01uf capacitor in parallel with the first cap also provides the second dip at f2 increasing the frequency response of the pair of caps.
The graphic above shows the benefit of placing two different value capacitors in parallel.
The impedance is reduced across a band of frequencies, adding the two nulls.
The first null is developed from the larger value capacitor, and the second null from the smaller value capacitor.
Placing a large value Tantalum capacitor next to a smaller value ceramic will cover a wide range of frequencies.
Placing two ceramic capacitors, a decade apart in value, in parallel will have the same effect but over a different frequency range.
Film Capacitors are Non polarized, and may be used in AC or DC circuits.
Typical values range form 1000pF to 1uF for Polyerster Film, and 0.01uF to 18uF for Metallized Film capacitors. Standard Film Capacitor values change in multiples of 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82.
Normal Temperature Coefficient [TC] for Film Capacitors is +7%.
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Load Life:After 2000 hours application of rated voltage at 85℃, capacitors meet the characteristics
| Capacitance Change | Within ± 20% of initial value (Within ± 25% of initial value for 4V) |
| Dissipation Factor | 200% or less of initial specified value |
| Leakage Current | Initial specified value or less |
In many applications capacitors need not be specified to tight tolerance (they often need only to exceed a certain value); this is particularly true for electrolytic capacitors, which are often used for filtering and bypassing. Consequently capacitors, particularly electrolytics, often have a tolerance range of ±20% and need to be available only within E6 (or E3) series values.
| Series | Values | |||||||||||
| E3 | 1.0 | 2.2 | 4.7 | |||||||||
| E6 | 1.0 | 1.5 | 2.2 | 3.3 | 4.7 | 6.8 | ||||||
| E12 | 1.0 | 1.2 | 1.5 | 1.8 | 2.2 | 2.7 | 3.3 | 3.9 | 4.7 | 5.6 | 6.8 | 8.2 |
Other types of capacitors, e.g. ceramic, can be manufactured to tighter tolerances and are available in E12 or closer-spaced values (e.g. 47 pF, 56 pF, 68 pF).
With the introduction of S.I. submultiples of micro, nano, and pico, it became customary to specify capacitors with a number between 1 and 999 followed by farad, microfarad, nanofarad, or picofarad. While supercapacitors of up to 5,000 farads are produced, it is not usual to use kilofarad or millifarad.
Although Electrolytic Capacitors have much higher levels of capacitance for a given volume than most other capacitor technologies, they can also have a higher level of leakage. This is not a problem for most applications, such as when they are used in power supplies. However under some circumstances they are not suitable. For example they should not be used around the input circuitry of an operational amplifier. Here even a small amount of leakage can cause problems because of the high input impedance levels of the op-amp. It is also worth noting that the levels of leakage are considerably higher in the reverse direction.
Unlike many other types of capacitor, electrolytic capacitors are polarised and must be connected within a circuit so that they only see a voltage across them in a particular way. The capacitors themselves are marked so that polarity can easily be seen. In addition to this it is common for the can of the capacitor to be connected to the negative terminal.
It is absolutely necessary to ensure that any electrolytic capacitors are connected within a circuit with the correct polarity. A reverse bias voltage will cause the centre oxide layer forming the dielectric to be destroyed as a result of electrochemical reduction. If this occurs a short circuit will appear and excessive current can cause the capacitor to become very hot. If this occurs the component may leak the electrolyte, but under some circumstances they can explode. As this is not uncommon, it is very wise to take precautions and ensure the capacitor is fitted correctly, especially in applications where high current capability exists.
Capacitor plague (also known as bad capacitors) is an ongoing problem with premature failure of large numbers of electrolytic capacitors of certain brands. Capacitors are used in various electronics equipment, particularly motherboards, video cards, compact fluorescent lamp ballasts, LCD monitors, and power supplies of personal computers. The first flawed capacitors were seen in 1999, but most of the affected capacitors were made in the early to mid 2000s. News of the failures (usually after a few years of use) forced most manufacturers to repair the defects and stop using the capacitors, but some bad capacitors were still being sold or used in equipment as of early 2007[update], and faults are still being reported as of 2011[update].Reference computer user reports on badcaps.net.
A serious quality control problem is that the issue only manifests after use over a period of time; poor quality electrolytic capacitors have the same measurable parameters as good ones when new. Only extensive accelerated life testing with high ripple currents and high operating temperatures can identify inferior components. After some normal use the bad capacitors fail predictably far sooner than normal end-of-life; most electronic components do not systematically fail in this way.
