Table of Contents
Capacitors in Series
When capacitors are connected in series, the total capacitance is always less than the smallest individual capacitor. This occurs because the effective plate separation increases while the charge on each capacitor remains the same. The voltage across the series combination equals the sum of the individual voltages.
Series capacitor connections are commonly used to increase voltage rating, create precise capacitance values, or distribute voltage stress across multiple components. In high-voltage applications, series connections allow the use of lower-voltage-rated capacitors to handle a higher total voltage safely.
Series Capacitance Formula
For two capacitors, this simplifies to:
Series vs Parallel
| Property | Series | Parallel |
|---|---|---|
| Total Capacitance | Decreases | Increases |
| Voltage Rating | Sum of ratings | Lowest rating |
| Charge | Same on all | Divides by capacitance |
| Voltage Distribution | Inversely proportional to C | Same on all |
Why Use Series Capacitors
- Increase voltage rating beyond individual component limits for high-voltage circuits.
- Obtain non-standard capacitance values from standard component values.
- Series capacitors in AC power systems compensate for inductive reactance in long transmission lines.
- Voltage balancing resistors are often placed in parallel with each series capacitor to ensure even voltage distribution.
Frequently Asked Questions
What happens to the total capacitance when capacitors are in series?
The total capacitance always decreases. For identical capacitors in series, the total is simply the individual capacitance divided by the number of capacitors. For example, three 300 μF capacitors in series give 100 μF total.
Why would I want less capacitance?
The primary reason for series connection is to increase voltage handling capability. If you need a 100V capacitor but only have 50V-rated parts, two identical capacitors in series can handle 100V total. Series connections are also used to fine-tune capacitance to specific values needed in filter circuits.
Do series capacitors need balancing resistors?
Yes, in many applications. Capacitors have leakage current variations that can cause unequal voltage distribution. High-value resistors (100k-1M ohm) placed across each capacitor equalize the DC voltage distribution and prevent overvoltage on any single component.