Attention of Aluminum Electrolytic Capacitors.

Attention on Application of Aluminum Electrolytic Capacitors

1)   DC electrolytic capacitors should be used polarized.

When reverse voltage is applied on DC electrolytic capacitor, the capacitor will becomes Short-circuited please use no polarized capacitors in the circuit be damage due to abnormal current flows the through the capacitors since the circuit where the positive voltage may be applied to the cathode terminal.

2)   Use capacitor within rated voltage

When capacitor is used at higher voltage than the rated voltage, leakage current increases, characteristics drastically deteriorate and damage in a short period may occur as a result. please take extra caution that the peak voltage should not exceed the rated voltage.

3)   Charge and discharge application.

When aluminum electrolytic capacitors for general purpose are employed in rapid charge and Discharge application, its life expectancy may be shortened by capacitance decrease, heat rise, etc.

4)  Store the capacitor.

I creased leakage current is common in aluminum capacitors which have been stored for long period of time. The Higher the storage temperature, the higher the leakage current increase, therefore please take precautions concerning the storage location. The leakage current decreases gradually as voltage are applied to the capacitor. In cases where increased leakage current causes problems in the circuit, apply voltage (aging) before using.

Environmental Category 25/105/21

Store temperature range≤35°C;

Humidity range≤75%RH

5)   Ripple current applied to capacitor should not exceed the rated value.

Excessive heat will reduce capacitance and result in shortened life of capacitor if ripple currents exceeding the specified rated value are applied. The peak value of the ripple voltage should be less than rated voltage.

6)  Ambient temperature.

Life of the aluminum electrolytic capacitors is affected by the ambient temperature .It is generally stated, that life doubles for each 10°C decrease in temperature.

7)  Lead stress

When a strong force is applied to the lead wires or terminals, stress is put on the internal connections. This may result in short circuit, open circuit or increased leakage current. It is not advisable to bend or handle a capacitor after it has been soldered to the PC board.

8)  Heat resistance at the soldering process

In the dip soldering process of PC board with aluminum electrolytic capacitors mounted, secondary shrinkage or crack of  PVC sleeve may be observed when solder temperature is too high or dipping time is too long.

9)  Hole pitch and position of PC board

A PC board must be designed so its hole pitch coincides with the lead pitch (lead spacing) of the capacitor specified by the catalog or specifications. When a capacitor is forcibly inserted into an unmatched hole pitch, a stress is put on the leads This could result in a short circuit or increased leakage current.

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Aluminum electrolytic capacitors'defect.

Aluminum electrolytic capacitors have always been a popular choice for power supply，Because of its low cost. However, their life have limited , and easy to infulenced by extreme conditions,main problem is high temperature and low temperature. Aluminum Electrolytic capacitors is made by aluminum foil and electrolyte.This electrolyte will evaporate during the life of the capacitor, it will change its electrical properties step by step. If the capacitor fails, it will be violent reactions: release flammable, corrosive gases.

The electrolyte evaporation''s speed all depend on capacitor temperature.Operating temperature dropped 10 degrees, the capacitor''s life will be doubled. Usually,The capacitors''life usually means under maximum rated temperature. The typical rated life is 1000 hours at 105 degrees Celsius. In the application of LED which requirement life time 25000hours, the aluminum electrolytic capacitor will have problem. Cause if want to reach to 25000hours, the working temperature should not more than 65°C. But LED working temperature can reach to 125°C at most.Though some famous manufacturer declare their can reach. but aluminum electrolytic capacitors still is limited LED Lamp''s life.

How to slove the problems? First, you may be chose to increase the rated voltage of the capacitor, to reduce the probability of electrolyte failure. However,the way will make the capacitor equivalent series resistance (ESR) more higher than before. Since the capacitor will generally have a high ripple current stress, so this high internal resistance will bring additional power consumption and increase the capacitor temperature. Failure rate will increases by increasing temperature. When the capacitor temperature is low, ESR increased dramatically. In this case,-40°C, the resistance increases by orders of magnitude. This will affect the power performance in many ways. If the capacitor is used for output of a switching power supply, the output ripple voltage was increased by orders of magnitude. Further, in the above zero frequency and the output capacitor ESR is formed, which allows an order of magnitude increase in the loop gain, which affects the control loop. This produces a stable oscillation power. In order to meet this strong vibration, the control loop will usually make a huge compromise in terms of space and operate at higher temperatures.

In short, the aluminum electrolytic capacitor is typically the lowest cost option. However, you will need to determine whether the application of its shortcomings adversely affected. Through its operating temperature you need to consider their longevity. meanwhile, you should appropriately reduce the rated voltage, so that you can achieve the lowest temperatures, and thus get the longest life. Finally, you need to understand the ESR range must be used so that you can properly design the control loop, to meet the ripple specifications.
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