～Things You Need to Know about Safety～
A power supply is a device that converts and provides electrical energy. It is designed and manufactured with utmost care for safety, but internally has electronic circuits that operate at high voltage (several hundreds of volts) and large current. Therefore, under wrong usage, it may cause abnormal heat and smoke, and in worst case, fire.
In this page, we will introduce examples leading to smoke and fire that are likely to occur according to various causes.
Also, please refer to instruction manual of individual product to ensure safe and proper usage
▶ １．Avoid using beyond the lifetime
The life span of the power supply is generally determined by the lifetime of the electrolytic capacitor. At the end of life of the electrolytic capacitor, internal resistance increases causing abnormal heat which results into internal pressure build-up that forces the safety valve to open.
Gaseous electrolyte is released and liquid electrolyte may leak out from the terminal area.
- Due to long-term use, the airtightness of the electrolytic capacitor was lost, and the internal electrolyte leaked out.
This leakage created tracking path between patterns on the PCB board causing subsequent failures such as sparks and smoke.
▶２．Avoid using under high temperature environment
When used under high temperature environment, electrolytic capacitor life will be shortened. (In generaly, as the ambient temperature rises by 10°C, the life of the electrolytic capacitor decreases to about 50%) .
When the electrolytic capacitor reaches the end of its life, the capacitor may generate heat abnormally and cause an open valve failure (see item 1). Take care to reduce the power supply ambient temperature as much as possible.
- Since the air flow around the power supply was poor and the power supply was used in an ambient temperature beyond the allowable specification, causing the electrolytic capacitor reached its end of life earlier.
There were also cases where the electrolyte inside leaked out and created tracking path on the PCB board causing smoke emission.
▶３．Be careful about conductive foreign matter or contamination penetration
Fire or smoke emission from foreign matter inside the power supply might occur due to abnormal heat caused by spark ignition or tracking phenomena resulting from continuous electrical bias on unexpected path created by adherence of conductive foreign matter and dust to high potential areas (several hundreds of volts).
- Abnormal heat was generated at a high potential location due to mixture of metal pieces, dust, and liquid inside the power supply, resulting into substrate burn out.
- Dust accumulated inside the power supply and tracking phenomenon occured at high potential location, causing on the PCB board to emit smoke or burn out.
▶４．Avoid placing flammable materials around the power supply
If flammable objects are placed around the power supply, unexpected carbonize may generation occurs due to an accidental failure of the power supply or any abnormality (tracking phenomenon or spark).
Fire might spread to these flammable objects, and may even spread to the casing of customer equipment.
※Take caution of the following flammable materials : relatively thin materials such as acrylic board, plastic board, paper, wood board etc.
- Power supply failure occurred when the power supply was placed in a plastic bag and installed in order to prevent end-user from touching the live part of the power supply. Eventually, the bag ignited and burned.
- A thin plastic plate was placed around a power supply to prevent electric shock during maintenance. The power supply failed and caused small spark from an internal component which ignited the plastic plate and then spread around the entire surrounding device enclosure.
▶５．Do not apply excessive mechanical stress
Mechanical stress while handling a power supply causes cracks in soldering and multilayer ceramic capacitors. The failure location may generate abnormal heat due to concentration of current caused by solder cracks or insulation failure due to capacitor cracks, and it will cause smoke or burnout.
- Dropping the power supply or applying shock caused microcracks in the multilayer ceramic capacitor. In this case, heat generation happened due to increased loss caused by insulation deterioration inside the capacitor. This caused the burning and tracking phenomena on PCB, it caused smoke emission and further damage.