1. INPUT VARISTOR FAULT
It is the most common type of failure we encounter in LED drivers. The varistor is the circuit element that protects the system against high voltage. Varistor failure us;
• Increase in voltage in the network,
• Neutral loosening or breaking,
• Indicates problems such as applying high voltage at the first installation.
Varistor bursts in various LED drivers.
The reasons for the increase in the Phase-Neutral voltage can be listed as follows;
• Inadvertently connecting a phase conductor instead of neutral at any point of the network,
• Breaking of the neutral conductor during a work in the network,
• Breaking of the neutral conductor by any external factor,
• Loss of contact as a result of loosening or oxidation of the neutral conductor at any point of the network (LV panels, building entrances (building junction box), overhead line jumping points, etc.) from the transformer,
• If the operational grounding is broken or has a very high value, high voltage may be continuously applied to the devices, and in this case, the devices will be damaged.
The voltage rise in 1 or 2 phases due to neutral break is shown on the side. Due to the rule of symmetry, while the voltage will increase in some phases, the voltage will decrease in others. In momentary neutral relaxation, the voltage will momentarily rise above the varistor limit value and the varistor will explode.
In electrical installations, as a result of the breaking / breaking of the common neutral line going to the consumers due to bad weather, etc., loosening or oxidation of the connections, situations occur that cause overvoltage and damage to some devices.
In order to prevent this problem, systems should be installed on the entire building-meter output, which will automatically open the circuit in case the voltage / voltages fall below or exceed the determined limits by continuously controlling the voltage / voltages between all phases and neutral, and provide feedback when the voltage reaches normal level.
Example of neutral break:
There are 4 subscribers receiving energy from the same branch of a distribution transformer. It is assumed that there is no operational grounding at the pole at the end of the network and the neutral is broken at the ① point of the distribution network. Since the one-phase A1-A2-A3-A4 receivers, which receive energy from the distribution network after the ① point where the neutral conductor breaks, are disconnected from the neutral instead of the phase-neutral voltage, the A1 and A3 receivers will be in series with each other and will be exposed to the voltage between phases L1-L2. The same situation will occur for A2-A4 receivers. However, in the A5 device, which continues to take the neutral line from the transformer behind the ① point, there will be no situation that will cause a malfunction as the phase-neutral voltage will not change.
The feeds of the lighting fixtures are connected through the R-S-T phase, in case of a momentary neutral break from the distribution company or the installation, the luminaire neutral circuit connected to the R phase is completed from the other phase.
varistor; It is a circuit element whose resistance changes with voltage and does not fail unless a voltage exceeding its value is applied. Its task in the circuit is to minimize the fault by damping the voltage pulses.
In the event that the instantaneous neutral line does not come in the luminaires connected to the R and S (380V) phases (This can usually be caused by the distribution company), the luminaires connected to the R phase complete their circuit from the S phase, that is, they are directly exposed to 380V voltage. malfunctions occur. Sometimes the voltage is so severe that the supply input terminals and varistors break off from the solder points on the PCB.
Users must learn the reasons for the instantaneous increase in voltage in the enterprise and take the necessary precautions. Support can be obtained from the Chamber of Electrical Engineers for the determination. https://www.emo.org.tr/
2. ARC FORMATION IN THE TERMINAL
There may be an arc-induced fault in the driver output terminal. A similar situation can be seen in the power supply cable at the input terminal). As can be seen in the picture below, arcing may occur in the cable. This is because the stranded wire used is not properly connected to the terminal, and some wires are outside the terminal socket.
To prevent this, the wires of the multi-wire cable should be gathered together with a ferrule or solder, and the terminal screw should be tightened with the appropriate torque. A loose screw will cause the cable to get rid of the terminal, and a screw tightened with too much torque will prevent the screw from fulfilling its pressing task by licking. This also applies to the input terminals, the same precautions must be taken at the input.
Errors such as the following may occur when stripped excessively and connected without the cable fringes being gathered properly.
To prevent arcing in the terminal;
It is important to prepare the cables for connection using the cable stripper. Properly prepared cables will help you to minimize the error. If the cables are then connected to the connector with a torque adjustable screwdriver, it will be easier to prevent this malfunction. You can create instructions for it depending on your workflows in production.
Break in circuit elements
As a result of the LED driver or electronic ballasts falling from a height, breakages may occur in the connection solders of circuit elements such as transformers and capacitors.
In order to prevent these malfunctions, LED drivers should not be exposed to severe mechanical forces by being very careful during their transportation to production after the entrance control in your factory. You can create migration-related instruction that will depend on your workflows in production.
Pulling out the cable without pressing the upper terminal release spring in push-in terminals and without loosening the screw on screw terminals. In this case, tension will occur in the terminal connection legs due to the pulling force and the terminal will break from the circuit.
In addition, using cables with a larger cross-section than allowed in push-in terminals will also damage the terminal and prevent a healthy connection. The cable cross-sections specified on the LED driver must be strictly followed.
Screw should be loosened completely and full pressure should be applied to the spring.
Break in Push-in Terminal
3LED DRIVE DOESN’T WORK OR THE LEDS ARE FLICKER FREQUENTLY
Temperature control in electronic ballast or led drivers is done from the TC control point on them. In addition, the operating ambient temperature of the drive is given in the product data sheets.
If the working ambient temperature is high or the TC point is high due to the armature design, the components on the electronic circuit will be adversely affected by the high temperature and serious reductions will occur in their lifetimes.
The most easily affected component is the capacitor, and swelling will occur in this liquid capacitor, as a result of which blink-like flashes will be seen on the LEDs. If the capacitor is exposed to higher temperatures, chemicals such as boric acid in the capacitor will flow and cause a malfunction in the circuit.
As a result of faulty design, the LED driver is directly exposed to the high temperature of the LED modules and causes yellowing on the outer bodies, causing malfunctions in the circuit elements.
To prevent the LED driver from failing and flicker before completing its life;
The amount of heat produced in LEDs basically depends on the driving current and LED efficiency. As the driving current passing through the LED increases, the electrical power and luminous flux it draws increase.
On the other hand, as the electrical power increases, the heat released also increases. Therefore, larger cooling surfaces are needed for LEDs driven at high currents.
LED efficiency can be defined as the ratio of the optical power emitted by the LED to the electrical power it draws.
As a result, efficiency also depends on temperature and driving current. As the temperature increases, the LED efficiency decreases.
In thermal modeling of LED luminaires, it is important to correctly determine the amount of heat emitted by the LED modules used in the luminaire. For this reason, optical, thermal and electrical measurements of the LED modules to be used before the thermal design should be made and their thermal powers should be calculated for different current and temperature levels.
Basic principles in LED luminaire design:
Lighting fixtures are structures that house light sources.
They include light sources, optical elements to disperse light, holders and connectors to protect, position and electrically connect light sources, and mechanical fasteners for assembly and protection.
Lighting fixtures are designed to perform the following functions:
• Distributing the luminous flux from the light source in a controlled manner
• To provide the necessary electrical connection for the light sources inside
• Physically protecting the light source
• To be highly efficient
• To be resistant to usage conditions
• Being Safe
The size, material, optical, thermal and electrical designs of the luminaire vary according to the type of light source used.
For efficient applications, luminaires must be designed correctly in terms of optics, thermal-mechanics and electricity.
Positioning of the driver in the LED luminaire design:
The healthy transfer of heat emitted by the operation of components such as the LED module and driver inside the luminaire is the most important factor for the life of the components.
It is necessary to position the components within the armature at optimum distances that will be least affected by each other.
Faults can be minimized in luminaires that provide good heat evacuation.
Pay attention to the distance between the components!!
- Failure in products exposed to high humidity
Electronic ballast and LED drivers must be chosen according to the application. For example, in IP20 drives to be used outdoors, luminaires must have higher IP protection than IP54. Luminaires with high IP protection must also have ventilation plugs (according to ventilation) when working in humid environments. This prevents moisture from being trapped inside.
Failure as a result of moisture
Malfunctions as a result of mechanical impacts
Drivers should not be exposed to any mechanical impact. During transportation, storage and assembly; drilling, cutting, falling from height, heating, etc. must be protected from mechanical effects.
The outer body of the driver was punctured as a result of the uncontrolled force applied during screwing and the coil inside was damaged.
Failure of the LED driver by exposure to dust
If IP20 drives are to be used in industrial facilities with dust/sand circulation in the environment, the luminaire must be min. It should be in IP54 protection class. Otherwise, dust adhering to the components will damage them and prevent the cooling of the electronic circuit.
- Failure of the LED driver by exposure to dust
To prevent this type of malfunction;
First of all, during the design, when the parts of the luminaire body are assembled, its sealing against the entry of dust and foreign substances must be done very well. The second important point is that the luminaires should be cleaned and maintained periodically. Lighting systems work more efficiently when they are maintained. Dust accumulates on the light source over time, reducing the amount of useful light. A dusty fixture can absorb almost half of the light. By keeping the fixtures clean, the amount of lighting can be increased without consuming more energy. Since the light output of all lighting sources will decrease over time, higher efficiency can be obtained in a longer time from regularly cleaned luminaires.
Entry of creatures such as insects/flies into the driver
Living things such as flies or insects that enter the LED driver can cause a short circuit on the circuit elements. For this reason, in order to prevent the entry of harmful organic or inorganic substances, both the gaps in the luminaire must be closed and the necessary protective measures must be taken by examining the environmental conditions of the luminaire’s working environment.
Insects detected inside the driver
Unstable operation of LED driver
If the LED load is complaining about unstable or unstable operation (such as light flickering), it is understood that the LED driver is used outside of its specifications. For example, the Urated (V) load range given in the product data sheet and on the driver. It must be used within the drivers’ typical operating ranges.
Tc operating temperature of LED driver:
Despite the use of high quality components, a higher failure rate and a reduction in operating life can be observed under inappropriate operating conditions where the permissible Tc temperature is exceeded. Our strict rule to ensure that the product life is not shortened and the failure rate is kept at a minimum level is as follows:
“Working Tc above 10°C means half life. Therefore, Tc limit should never be exceeded!”