boylesg said:
What happens to them if their voltage limit is exceeded by a small amount over a period of time?
Do they buldge as they do when you apply a reverse voltage?
Click to expand...
Marked voltage rating on capacitor body is maximum safe voltage, capacitor can handle voltage over that but that is specified in manufacturers datasheet.
What can happen in over temperature and over voltage situations :
See these videos:
https://www.youtube.com/watch?v=_WheLp0RdLQ
https://www.youtube.com/watch?v=3b7mjukhTyQ
Rated DC Voltage
Rated DC voltage is the nominal voltage marked on the capacitor, and it is the maximum peak voltage including ripple voltage that may be applied continuously between the terminals and over the rated temperature range. Higher rated voltage capacitors may be substituted for lower rated voltage capacitors as long as case size, DF, and ESR ratings are also compatible.
Rated Surge Voltage
Rated surge voltage is the maximum DC overvoltage to which the capacitor may be subjected at 25ºC for short periods not exceeding approximately 30s at infrequent intervals of not less than 5 min.
Surge voltage Measurement
Subject the capacitors to their rated surge voltage at normal room temperature and through a 1000Ω ±10% resistor (except for capacitances of 2500μF and up, use a higher value resistor calculated as 2,500,000/CΩ ±10% where C is the capacitance in μF). Cycle the voltage ½ minute on followed by 4½ minutes off during which each capacitor is discharged through the charging resistor or equal resistor. Repeat the cycles for 120h. Post test requirements are for DCL, ESR and DF to meet initial requirements and for there to be no evidence of mechanical damage or electrolyte leakage. Electrolyte residue with no droplets or visible flow is permitted.
Reverse Voltage
Aluminum electrolytic capacitors are polarized and must be connected in the correct polarity. They can withstand reverse voltages up to 1.5V. Higher reverse voltage can cause failure by pressure build up and rupture of the capacitor’s safety vent structure. Non-polar and semi-polar devices are available that can withstand reverse voltage.
Transient Overvoltage
Aluminum electrolytic capacitors can generally withstand extreme overvoltage transients of limited energy. Application of overvoltage more than about 50 V beyond the capacitor’s surge voltage rating causes high leakage current and a constant-voltage operating mode quite like the reverse conduction of a zener diode. The capacitor may fail short if the electrolyte cannot take the voltage stress, but even if it can, this operating mode cannot be maintained for long because hydrogen gas is produced by the capacitor, and the pressure build up will cause failure. However, special designs are available that use the overvoltage, zener-clamping effect to successfully protect equipment from overvoltage transients such as lightning strikes.
Capacitors used as bus capacitors in large, high-voltage capacitor banks are less capable of withstanding overvoltage transients because the high energy and low source impedance of the capacitor bank can prevent a momentary partial discharge from self healing and cause it to become a runaway short-circuit failure. For high-voltage capacitor-bank applications use capacitors proven for that use.
:wink:
Marked voltage rating on capacitor body is maximum safe voltage, capacitor can handle voltage over that but that is specified in manufacturers datasheet.What can happen in over temperature and over voltage situations :See these videos:Rated DC voltage is the nominal voltage marked on the capacitor, and it is the maximum peak voltage including ripple voltage that may be applied continuously between the terminals and over the rated temperature range. Higher rated voltage capacitors may be substituted for lower rated voltage capacitors as long as case size, DF, and ESR ratings are also compatible.Rated surge voltage is the maximum DC overvoltage to which the capacitor may be subjected at 25ºC for short periods not exceeding approximately 30s at infrequent intervals of not less than 5 min.Subject the capacitors to their rated surge voltage at normal room temperature and through a 1000Ω ±10% resistor (except for capacitances of 2500μF and up, use a higher value resistor calculated as 2,500,000/CΩ ±10% where C is the capacitance in μF). Cycle the voltage ½ minute on followed by 4½ minutes off during which each capacitor is discharged through the charging resistor or equal resistor. Repeat the cycles for 120h. Post test requirements are for DCL, ESR and DF to meet initial requirements and for there to be no evidence of mechanical damage or electrolyte leakage. Electrolyte residue with no droplets or visible flow is permitted.Aluminum electrolytic capacitors are polarized and must be connected in the correct polarity. They can withstand reverse voltages up to 1.5V. Higher reverse voltage can cause failure by pressure build up and rupture of the capacitor’s safety vent structure. Non-polar and semi-polar devices are available that can withstand reverse voltage.Aluminum electrolytic capacitors can generally withstand extreme overvoltage transients of limited energy. Application of overvoltage more than about 50 V beyond the capacitor’s surge voltage rating causes high leakage current and a constant-voltage operating mode quite like the reverse conduction of a zener diode. The capacitor may fail short if the electrolyte cannot take the voltage stress, but even if it can, this operating mode cannot be maintained for long because hydrogen gas is produced by the capacitor, and the pressure build up will cause failure. However, special designs are available that use the overvoltage, zener-clamping effect to successfully protect equipment from overvoltage transients such as lightning strikes.Capacitors used as bus capacitors in large, high-voltage capacitor banks are less capable of withstanding overvoltage transients because the high energy and low source impedance of the capacitor bank can prevent a momentary partial discharge from self healing and cause it to become a runaway short-circuit failure. For high-voltage capacitor-bank applications use capacitors proven for that use.:wink: