Temperature of LED: Do Electrolytic Capacitors Significantly Shorten LED Lifespan?

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It is widely believed that the reduced lifespan of LED lamps is mainly due to the brief lifespan of the power supply, which is frequently linked to the short durability of electrolytic capacitors. With the market flooded with low-quality, ephemeral electrolytic capacitors amid fierce pricing competition, some manufacturers of LED lighting choose these subpar components, thereby sacrificing quality. This choice not only impacts the overall lifespan but also the temperature of LED units, as poor quality components can exacerbate heat issues.

Understanding Electrolytic Capacitor Lifespan

The lifespan of an electrolytic capacitor is crucially dependent on the ambient temperature during operation. Lifespan is typically measured in hours. For example, a capacitor with a lifespan index of 1,000 hours doesn’t necessarily fail after that period but will have its capacity reduced by half—from 20uF to 10uF.

Moreover, it’s essential to specify the working temperature when discussing a capacitor’s lifespan index. Electrolytic capacitors, which utilize a liquid electrolyte, are commonly rated at an ambient temperature of 105°C. At higher temperatures, the liquid electrolyte evaporates more quickly, decreasing the capacitor’s lifespan. Thus, a capacitor rated for 1,000 hours at 105°C will have a shorter lifespan if the ambient temperature rises above 105°C and a longer lifespan if the temperature falls below this threshold.

Temperature Versus Lifespan: The General Rule

The relationship between temperature and capacitor lifespan can be estimated simply: for every 10-degree increase in ambient temperature, the lifespan halves; conversely, for every 10-degree decrease, it doubles. While this rule provides a rough estimation, it’s generally quite accurate.

Given that electrolytic capacitors in LED drivers are housed within the LED fixtures, understanding the internal temperature of these fixtures is key to determining the working life of the capacitors.

Understanding Ambient Temperature in LED Lamps

In many LED lamps, both the LED and the electrolytic capacitors are housed together, sharing the same environmental conditions. The ambient temperature inside the lamp is primarily influenced by the balance between the heat generated and dissipated by the LED and the power supply. Given that each LED lamp has its own unique heating and cooling dynamics, determining the internal ambient temperature might seem challenging.

However, the internal ambient temperature of a well-designed LED lamp should remain consistent. This stability is crucial as the junction temperature of the LED chip largely determines the LED’s light decay and overall lifespan. The LED junction temperature itself is influenced by the ambient temperature surrounding the LED, so knowing the permissible junction temperature allows for the calculation of the LED lamp’s internal temperature.

Temperatures of LED PCB board

To understand this better, consider the thermal resistances involved:

• Thermal Resistance θjc: This is the resistance from the LED chip’s junction to the case.
• Thermal Resistance from the LED case to the aluminum substrate surface: This involves several layers including solder, copper foil, and insulation, with the insulation layer’s resistance being particularly significant, known collectively as θlv.
• Thermal Resistance θla: This is from the aluminum plate to the air inside the lamp housing.

Taking the example of a 3014 type LED, its thermal resistance θjc is 90°C/W. With a power of only 0.1W, the internal to external temperature differential is approximately 9°C. Assuming the thermal resistance of the aluminum substrate is 1°C/W and considering a 10W LED lamp where all LEDs are mounted on the same substrate, the total temperature difference amounts to 19°C. Estimating the final θla can be tricky as it depends on air circulation within the lamp; with stagnant air, the difference might be around 1°C, totaling a 20°C difference. Thus, the junction temperature of the LED would be the ambient temperature plus 20°C.

But is an internal ambient temperature of 105 degrees permissible? To answer this, let’s examine a graph below depicting the relationship between the junction temperature of Cree’s LED chips and their light attenuation, providing further insight into the thermal dynamics within LED lamps.

Temperature and Life Decay

If the ambient temperature reaches 105°C, then the junction temperature would rise by an additional 20°C, resulting in a junction temperature of about 125°C. At this level, the lifespan of the LED is significantly reduced to approximately 4,000 hours, which is generally considered unacceptable. Thus, it is crucial that the ambient temperature inside an LED lamp is maintained well below 105°C to ensure longevity.

To determine the optimal ambient temperature for LED longevity, consider if the desired lifespan is 100,000 hours. In such a case, the junction temperature should not exceed 65°C, which means the ambient temperature must be kept below 45°C. Therefore, to achieve this lifespan, the electrolytic capacitor’s working ambient temperature must also remain below 45°C. This approach helps in defining the necessary conditions for ensuring the durability and efficiency of LED lighting.

Determining the Real-World Lifespan of Electrolytic Capacitors at 45°C Ambient Temperature

Understanding the optimal working ambient temperature for electrolytic capacitors in LED lamps allows us to accurately predict their actual lifespan. Below, we have compiled a table displaying the real-world lifespans of various commonly used electrolytic capacitors when operating at an ambient temperature of 45°C.

Electrolytic Capacitors Life

The table illustrates that even the most basic electrolytic capacitors, typically rated for 1,000 hours, can achieve a lifespan of up to 64,000 hours when operated at an ambient temperature of 45°C. This extended lifespan is more than sufficient for standard LED lamps advertised with a 50,000-hour life expectancy.

Strategies to Enhance the Lifespan of Electrolytic Capacitors

Improving Design for Longer Life

Extending the life of electrolytic capacitors is straightforward, as their lifespan typically ends due to the evaporation of the liquid electrolyte. Enhancing the seal to prevent evaporation naturally prolongs their functionality. Additionally, using a phenolic plastic cover that encompasses the capacitor, coupled with a double gasket that fits snugly within the aluminum casing, can significantly reduce electrolyte loss.

Optimizing Usage for Extended Lifespan

Another method to increase the lifespan of electrolytic capacitors is by reducing their ripple current. If the ripple current is excessively high, using two capacitors in parallel can mitigate this issue and thereby extend the service life.

Selecting the Appropriate Capacitor

When choosing electrolytic capacitors, it’s crucial to opt for reputable brands to ensure quality. It’s also important to allow for adequate margins in terms of voltage and capacity. For instance, for a DC voltage of 220V post-bridge rectification, which can surge up to 300V, capacitors rated at least at 450V should be used. Similarly, if calculations suggest a need for a 10uF capacitor, opting for a 20uF capacitor is advisable. These precautions help mitigate the effects of the capacitor’s equivalent resistance and ripple current, which can elevate its internal temperature above the ambient level, thus necessitating some buffer for safety and longevity.

Ensuring the Protection of Electrolytic Capacitors

Sometimes, even when long-life electrolytic capacitors are used, failures still occur. Why might this happen?

It’s a misconception to blame the quality of electrolytic capacitors alone for these failures. In reality, the capacitors are often not the cause but the victims of external conditions. The primary culprit in many cases is the AC grid voltage fluctuations common in city power systems, where lightning surges can induce momentary high-voltage spikes. Despite comprehensive lightning protection measures on large power grids, some leakage into residential areas is almost inevitable.

For LED lighting systems powered by city electricity, it is crucial to implement surge protection measures at the power supply’s mains input terminals. This includes installing fuses and over-voltage protection resistors to safeguard the circuit components, including the electrolytic capacitors. Without these protective measures, even high-quality, long-life capacitors are susceptible to damage from surge voltages.

If you have any questions or need assistance selecting the right LED lighting fixtures, please reach out to us directly. Our lighting experts are here to ensure you receive the optimal lighting solutions for your needs.

FAQs About Temperature of LED