When is the capacity the same

Series connection of capacitors

A series connection of capacitors is given when the same alternating current or charge / discharge current (direct current) flows through all capacitors.
The series connection of capacitors causes a reduction in capacitance, comparable to an increase in the distance between the plates with the same plate area.
Sometimes the series connection is also called a series connection. No matter how, the capacitors are always connected in series.

  • Often a calculated capacitance is not available as a capacitor. Instead, two or more capacitors are connected in series to get the calculated value.
  • At high voltages, several capacitors are connected in series to prevent the risk of a breakdown. It is helpful here that the total voltage is divided across the capacitors.

Behavior of tensions

The total voltage Utotal divides at the capacitors in the series connection. The sum of the partial voltages is equal to the total voltage. The greatest voltage drops at the smallest capacitance. The smallest voltage drops at the largest capacitance.

Behavior of capacity

The total capacity of the series connection is smaller than the smallest individual capacity. Each additional series capacitor reduces the total capacitance.

Behavior of the loads

The charges on the capacitors are the same.

Series connection of two capacitors

If only two capacitors are connected in series, the equation for calculating the capacitance can be simplified.
or

What to consider when connecting capacitors in series in practice

When capacitors are connected in series, you want the Advantage of the lower partial voltages make use of. In purely mathematical terms, the total voltage is divided between the capacitors connected in series.
But prevail at the moment of switch-on undefined states, at which point a capacitor can break. However, it is also possible that the destruction only takes place after a long period of time and during operation. Each type of capacitor behaves differently.

Electrolytic capacitors, especially when they are older, form when a voltage is applied. If there are electrolytic capacitors in the series connection, which do not have this effect, then under certain circumstances the full voltage is applied to one capacitor while the others are forming. Electrolytic capacitors without formation can be damaged.
A series connection of electrolytic capacitors should only be made if there is no capacitor with a sufficiently high nominal voltage. For example with high-voltage power supplies.

When using unpolarized wound and ceramic capacitors in a series connection, a distinction must be made between alternating voltage and direct voltage.
Such capacitors have a tolerance of up to plus-minus 20%. This tolerance must be included in the calculation of the individual nominal voltages. Depending on the capacity tolerance, the nominal voltage of an individual capacitor must be significantly higher than the calculated partial voltage.

The following rule applies: When determining the correct nominal voltage, one must not simply divide the total voltage by the number of capacitors connected in series, but must consider the capacitance tolerance, which increases the individual nominal voltages.

It is particularly important to note that the Destruction of the capacitors can be done when sent to the AC voltage are switched, when this is at its peak.
The steep switch-on edge that occurs is comparable to a very brief HF current. The capacitor typically has a very low capacitive resistance, which results in a high peak current. Therefore, a resistor is connected in series with the capacitors, which ensures a certain current limitation.

What about DC voltage? In practice, the tension is distributed unevenly. This is due on the one hand to the different tolerances of the capacitances, but also to the extremely high-ohmic leakage resistance in the dielectric of the individual capacitors. These also have tolerance values.
The capacitors with higher resistance leakage resistors charge to a higher voltage than the others. This process can be avoided with less high-ohmic and defined resistors that are connected in parallel to the individual capacitors.

Without Precautions for voltage and current limitation you always have to expect the worst. Here you have to take into account that a capacitor suffers over time and breaks down at some point later. There are different deaths. Too high a voltage leads to an internal breakdown followed by a short circuit. With self-healing capacitors, a bit of the metal foil is evaporated when the breakdown occurs, resulting in a minimal reduction in capacitance. Over time, repetitions create an increasing imbalance in capacities.
And if one breaks due to a short circuit, the others will also bang, because they then get too much tension.

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