Summary of Avoid these common aluminum electrolytic capacitor pitfalls
Aluminum electrolytic capacitors, common in power supplies for their low cost, have limited lifetimes influenced strongly by temperature. Their electrolyte evaporates over time, changing electrical properties and potentially causing violent failure. Lifespan doubles for every 10°C drop in operating temperature and is typically rated at maximum temperature (e.g., 1,000 hours at 105°C). In long-life products like 25,000-hour LED bulbs, maintaining capacitor temperature below about 65°C is necessary, but high ambient temperatures and design constraints often make aluminum electrolytics the life-limiting component.
Parts used in theAluminum Capacitor Pitfalls:
- Aluminum electrolytic capacitor
- Foils
- Paper separator saturated with electrolyte
- Electrolyte (liquid that evaporates)
- LED light bulb (as application example)
Aluminum electrolytic capacitors remain a popular choice in power supplies due to their low cost. However, they have limited life and are sensitive to both hot and cold temperature extremes.
Aluminum electrolytic capacitors are constructed with foils placed on opposite sides of paper saturated with an electrolyte. This electrolyte evaporates over the capacitor’s lifetime, altering its electrical properties. If the capacitor fails, it can be spectacular as pressure builds up in the capacitor, forcing it to vent a combustible and corrosive gas.
The rate at which the electrolytic evaporates is a strong function of the capacitor’s temperature. For every 10 degree Centigrade decrease in operating temperature, the capacitor life is extended by a factor of two. Capacitor life ratings generally are specified at their maximum rated temperature. A typical rating might be 1,000 hours at 105 degrees Centigrade.
Selecting these capacitors for use in long-life applications, such as the LED light bulb shown in Figure 1, where the LED’s must operate for 25,000 hours is problematic. To achieve the full 25,000 hour life, this capacitor requires a temperature of no more than 65 degrees Centigrade.
This is particularly challenging, as the ambient temperature in this kind of application can exceed 125 degrees Centigrade. There are capacitors available that are rated for higher temperatures, but in most instances the aluminum electrolytic capacitor is going to be the life-limiting component of LED replacement bulbs.
For more detail: Avoid these common aluminum electrolytic capacitor pitfalls
- How does temperature affect aluminum electrolytic capacitor life?
For every 10 degree Centigrade decrease in operating temperature, capacitor life is extended by a factor of two, and life ratings are specified at maximum rated temperature. - What causes an aluminum electrolytic capacitor to fail spectacularly?
Evaporation of the electrolyte changes properties and can let pressure build, forcing the capacitor to vent combustible and corrosive gas. - Why are aluminum electrolytic capacitors problematic in long-life LED bulbs?
They have limited life that depends on temperature; to reach 25,000 hours the capacitor must run at no more than about 65 degrees Centigrade, which is difficult in typical high-ambient environments. - What is a typical life rating example for an aluminum electrolytic capacitor?
A typical rating might be 1,000 hours at 105 degrees Centigrade. - Can higher temperature rated aluminum electrolytics solve the lifetime issue?
Higher temperature rated capacitors exist, but in most instances aluminum electrolytics remain the life-limiting component of LED replacement bulbs. - What is the structure of an aluminum electrolytic capacitor?
It consists of foils placed on opposite sides of paper saturated with an electrolyte. - How high can ambient temperature be in LED bulb applications?
The ambient temperature in such applications can exceed 125 degrees Centigrade.
