Key points of selection of Aluminium electrolytic capacitor

Rated voltage

The capacity and withstand voltage marked on the body of Aluminium electrolytic capacitor are very important and are the most basic content for selecting capacitor.

In actual capacitor selection, larger capacitors should be used for areas with fast current changes, but it is not necessarily better to have larger capacities. Firstly, as the capacity increases, the cost and volume may increase. Additionally, the larger the capacitor, the greater the charging current and the longer the charging time. These are all considerations to consider in practical application selection.

Rated working voltage: The maximum DC voltage that a capacitor can withstand when operating reliably for a long time within the specified working temperature range. In AC circuits, it is important to note that the maximum AC voltage applied cannot exceed the DC operating voltage of the capacitor. The commonly used fixed capacitor working voltages include 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 200V, 250V, 400V, 450V, 475V, 500V, 600V, and 630V. The actual voltage that a capacitor must withstand in a circuit cannot exceed its withstand voltage value.

In the filtering circuit, the withstand voltage value of the capacitor should not be less than 1.42 times the AC effective value. Another important issue to note is the operating voltage margin, which should generally be above 15%.

Allowing the rated voltage of capacitors to have more margin can reduce internal resistance, reduce leakage current, reduce loss angle, and increase service life. Although the use of 50V Aluminium electrolytic capacitor with 48V working voltage will not cause problems in a short time, the service life may be reduced after a long time of use.

Dielectric loss

The energy consumed by a capacitor under the action of an electric field is usually represented by the ratio of the loss power to the reactive power of the capacitor, which is the tangent of the loss angle (in the equivalent circuit of a capacitor, the series equivalent resistance ESR is the same as the capacitance reactance 1/ ω The ratio of C is called Tan δ， The ESR here is the value calculated at 120Hz. Obviously, Tan δ It increases with the increase of measurement frequency and increases with the decrease of measurement temperature. The larger the loss angle, the greater the loss of the capacitor. A capacitor with a larger loss angle is not suitable for working at high frequencies. The dissipation factor (DF) exists in all capacitors, and sometimes the DF value will vary with the loss angle tan δ express. The lower this parameter, the better. But this parameter of Aluminium electrolytic capacitor is relatively high.

Whether the DF value is high or low is related to temperature, capacity, voltage, frequency, etc. for capacitors of the same brand and series; When the capacity is the same, the higher the withstand voltage, the lower the DF value. In addition, the higher the temperature, the higher the DF value, and the higher the frequency, the higher the DF value.

External dimensions

The external dimensions are related to weight and joint shape. Single ended is a radial lead type, screw is a lock screw type, and there is also a patch Aluminium electrolytic capacitor. Compared to two capacitors with the same capacity and voltage resistance, but different brands, the weight must be different; And the overall size is more related to the shell planning. Generally speaking, capacitors with the same diameter and capacity can be replaced by capacitors with lower heights. However, when replacing capacitors with lower lengths, the issue of mechanism interference should be considered.