Series & Parallel Capacitor Calculator
Combine up to six capacitors and see the equivalent capacitance, how the voltage divides, and whether each part stays within rating.
Step-by-step
- Enter valid values to begin.
Ideal capacitors at steady state or low frequency, with the applied voltage shared as an ideal capacitive divider (Vk = V × Ceq / Ck in a series string). Real electrolytic strings settle by leakage resistance, not capacitance, so use balancing resistors. The 80% voltage rule is a common derating practice, not a standard; follow the manufacturer derating for the part, ambient temperature and ripple. Leave a field blank to leave a capacitor out. Equal ESR is assumed for every capacitor in the optional ESR estimate.
Series and Parallel Capacitors: Charge Is Equal, Voltage Is Not
Core Engineering Principles
Parallel capacitors are the easy case: capacitances add, voltage is common, and each part stores charge in proportion to its size. Series strings are where people get hurt. The same charge flows onto every capacitor in the string, so voltage is inversely proportional to capacitance, and the smallest part takes the biggest share. Put 470 µF and 1000 µF across 48 V and the small one sees 32.7 V, not 24 V. If it is a 35 V part you are already at 93% of its rating, with no margin for ripple or a supply spike.
That ideal divider only describes the first moments. After a few minutes at DC, leakage current dominates, and the voltage divides by leakage resistance instead. Electrolytic leakage varies a lot between parts, even in the same batch, so one capacitor can drift toward the full bus voltage and vent. We fix this with equal balancing resistors across each capacitor, sized so the bleeder current is a good multiple of the worst leakage, typically around ten times. Film and ceramic parts leak far less, but we still derate: many designers keep working voltage at or below 80% of rated, and lower again at high temperature or with ripple.
Share: Vk = V × Ceq / Ck • Q = CeqV • E = ½ CeqV²
NEC & Standard References
IEC 60384-1 is the generic specification for fixed capacitors in electronic equipment and defines rated voltage, category voltage and temperature derating. Its sectional parts cover specific types, for example electrolytic and film. IEC 60063 supplies the preferred E-series capacitance values and tolerance codes. IEEE Std 100 and IEC 60050 define the terms. Check the datasheet for ripple-current rating and surge voltage, because neither is visible in a capacitance calculation.1. Ceq = 470 × 1000 / 1470 = 319.7 µF.
2. Charge Q = 319.7 µF × 48 V = 15.35 mC.
3. V1 = 48 × 319.7 / 470 = 32.65 V and V2 = 48 × 319.7 / 1000 = 15.35 V.
4. Energy = ½ × 319.7 µF × 48² = 0.368 J.
5. C1 is at 93% of its rating, above the 80% guide, so we fit two 63 V parts, or use matched parts with a balancing resistor on each. Equal parts would each hold 24 V.
- Never trust a series string without balancing. Equal resistors across each electrolytic keep the split near the ideal value.
- Unequal values make unequal voltage. The smaller capacitor takes more, so check each part against its own rating.
- Mind polarity. Polarised parts in series must all face the same way, and a reversed one can fail violently.
- Stored energy bites. Even small banks hold enough charge to hurt, so discharge them through a resistor before servicing.
- ESR sets ripple heating. Paralleling parts lowers ESR and shares ripple current, but only if layout keeps the paths equal.