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Power Supply & Controls
Larry, obtained a Master Degree in electrical-engineering primary focused around optics and solid state mechanics. Shortly after graduating , he was able to apply these skills as a Field Applications Engineer (FAE) working directly with clients in providing commercial, residential, and industrial solutions.
Dimming Control - How to Choose
What Is Power Factor
Class I vs. Class II vs. Class 1 vs. Class 2
How to Choose a Dimming Control?
August 01, 2016
Due to significant growth in the LED lighting market, how to choose a right dimmer for LED lighting fixtures is critical. Compatibility between LED fixture, drivers, and controls can be confusing, and if they are specified improperly, performance will suffer. Before choosing the dimming control, there are some factors need to be considered including lighting applications, required dimming performance, and control preferences.
The first thing we need to consider is the lighting applications. Is the LED fixture for new construction or retrofit? You can have variety of control options for new construction, but only have limited control options for retrofit. For retrofit application, the dimming option for LED lighting fixture is adapted to the existing dimming system.
Next is to know the desired dimming range. The dimming range of a lighting fixture is based on the performance of the driver. Choosing the right dimming control can reduce flicker and affect the ability to achieve the desired dimming range. However the dimmability, low-end light level, and performance of the product are determined by the driver.
Once we determine the dimming range, then the most important step is to choose the type of dimming control. There are many types of controls and control systems depending on the dimmability of drivers. It is either for primary side (high voltage), secondary side (low voltage) of the driver, or an additional device for embedded wireless connectivity. Most common types of dimming methods for drivers are:
Forward phase(leading-edge) dimming:
Reversed phase (Tailing-edge) dimming
All the wall dimmers or dimming control units have their unique wiring connections, please refer to manufacturer's wiring instruction for correct installation. By choosing the right driver and considering key issues, it will be easier than ever to dim the LED fixtures that meets performance and aesthetic expectations.
What is Power Factor
June 01, 2016
The Power Factor(PF) is the measurement of the relationship between the AC source voltage and current. Power factor can range from 0 to 1.0, with 1.0 being ideal. In a purely resistive AC circuit, voltage and current waveforms are in phase, changing polarity at the same instant in each cycle, and all the power entering the load is consumed. However, when reactive loads are present in the circuit such as capacitors or inductors, energy storage in the loads results in a phase difference between the current and voltage waveforms. During each cycle of the AC voltage, extra energy, in addition to any energy consumed in the load, is temporarily stored in the load in electric or magnetic fields, and then returned to the power grid a fraction of the period later. The non-productive power increases the current in the line, and cause lower power factor. Thus, a circuit with a lower power factor will use higher current to transfer a given quantity of real power than a circuit with higher power factor.
Besides Power Factor, we need to know what the Apparent Power is. When inductors and capacitors in the circuit, they dissipate zero power , yet the fact that they drop voltage and draw current gives the deceptive impression that they actually consume power which is called “reactive power.” The actual amount of power being used, or dissipated, in a circuit is called “True Power.” The combination of reactive power and true power is called apparent power, which is measured in the unit of Volt-Amps(VA).
Here is the relationship between Power Factor, True Power and Apparent Power:
Power Factor(PF)= True Power(W)/Apparent Power(VA) = W/VA
Power factor can be an important aspect to consider in an AC circuit, because any power factor less than 1 means that the circuit’s wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load. However, poor power factor can be corrected which is called power factor correction(PFC). PFC can be done by adding another load to the circuit drawing an equal and opposite amount of reactive power, to cancel out the effects of the load’s inductive reactance. Usually the power factor of transformers on the market is 0.7-0.85, and 0.9-0.95 for electronic drivers with PFC function.
What is the R9 value?
Why it is so important?
April 01, 2016
In lighting industry, Color Rendering Index (CRI) has been widely used for measuring the quality of light source. CRI values range from 1-100, with 100 rendering colors the best to natural sunlight. CRI is calculated from the differences in the chromaticity of eight CIT standard color samples (R1-R8), the smaller the average difference in chromaticity, the higher the CRI. However, new research indicates that the CRI value may not accurately describe how well LEDs render colors. For example, an LED can have a relatively high CRI but render red poorly.
The R9 value is one of the 14 pigment colors scientists have established to measure color rendition, and it produces strong, vibrant reds. It is important because strong reds are prevalent in skin tones, meat, fruit, and artwork. LED with higher R9 values produce the most vivid colors. However R9 is not measured in CRI. Sometimes LED with high CRI value might have negative R9 value, which is not good for more accurate representation of the actual color. Whether in an art gallery, hospital, restaurant, or residential home, the color red is critical in order for the human eye to interpret pure colors.
Title 24 is California's energy standard for new homes and commercial buildings, and it requires a 90+ CRI and R9 value of 50 or more as high quality, high efficacy light sources. So next time do not forget to ask about R9 value when you need high quality LEDs.
Class I vs. Class II vs. Class 1 vs. Class 2
March 01, 2016
In the electrical appliance manufacturing industry, the IEC protection classes are used to differentiate between the protective-earth connection requirements of devices. Depending on how exactly the protection is provided, electrical appliances are put into five classes of equipment construction., Class I, II, III, 0 and 01. Of these the most important are Class I and Class II.
In Class I appliances, the protection is provided by a combination of basic insulation and the use of electrical earth. These appliances must have their chassis connected to electrical earth by an earth conductor (colored yellow/green in most countries, green in the U.S., Canada and Japan).
To safeguard against electric shock from metal cased electrical appliances, the metal chassis or case or any exposed metal of appliances (other than double-insulated items) must incorporate a protective Earthing conductor connected to the Earth pin of an approved three pin plug incorporation an "Earth" terminal.
In a Class II appliance, the user is protected by at least two layers of insulation between the current carrying parts and any metal accessible to the user.
•Basic Insulation, and
For this reason, Class II appliances are also known as Double Insulated appliances. They do not require an Earth connection. In Europe, a double insulated appliance must be labelled " Class II", "double insulated" or bear the double insulation symbol (a square inside another square). If the basic insulation or the supplementary insulation breaks down, it will not result in an electric shock risk.
Are Class I and Class II appliances just as safe?
Class I appliance, one of the layers of safety is provided by the earth connection. For this to be effective, the wiring in the building has to be inspected regularly to check that the Earth in the mains socket is correctly taken to the local earth potential. Class I appliances depend on the external wiring in the building to fully provide the 2 levels of protection.
Class appliances however always provide 2 levels of protection irrespective of the status of the wiring installation. Both layers of the protection are built into the design making Class II appliances a lot safer than Class I appliances.
Class 1, 2 and 3 circuits are classified as remote-control, signaling, and
power-limited circuits in the National Electrical Code (NEC).
Class 2 and 3 circuits - The NEC defines Class 2 in chapter 9 NEC provides the power limitations for the power sources: on for AC current and one for DC current. In general, a Class 2 circuit (operation at 24V with a power supply durable marked " Class 2" and not exceeding 100VA) is the type most commonly used.
The NEC defines a Class 2 circuit as that portion of the wiring system between the load side of Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electrical shock.
Class 2 or Class II Power Supplies?
Class 2 - is a classification referring to the NEC - National Electric Code. to avoid potential cable overheating due to excessive currents and electric shock, the output of the power supply is limited to 60VDC or 100VA, (100W when used with an AC-DC power supply). You will often see 24V output DIN rail power supplies or LED drivers rated at 91W rather than 100W because if the power supply is overloaded, an tolerance in the over current protection has to be accounted for.
Class II - Refers to power supplies with either a double or reinforced insulation barrier between the input and the output. Class II supplies do not rely on an earth connection to protect against shock hazard. Many cell phone chargers and laptop power supplies are Class II. TDK-Lambda's DSP series also are Class II, having just a Line and Neutral AC input without a ground connection.
One advantage of Class II is better surge protection between input and ground and usually a lower earth leakage current.
February 01, 2016
What is voltage drop?
Voltage drop describes the energy(voltage) that a component uses when current flows in a circuit. Ideally, wires, connections and switches should never drop voltage. If one of these uses voltage, there won't be enough energy left to operate the real load. In general, most of the served loads, such as light fixtures, have much greater power consumption than wires (conductors) serving them. However, given enough distance and enough current, resistance found in wires will cause the voltage to drop large amount over the length of wires. In lighting industry, voltage drop of wires is critical and it will affect the performance of light source.
How does voltage drop play a role in design of fixture?
Typically, 3% or less is the recommended level for efficient operation of light fixtures. If the amount of voltage drop exceeds a certain level, it will result in poor performance, and decreased lifespan.
This is most commonly seen as dim light output from lights, and it is noticeable when many lights are wired in series. You will observe the brightness decreases as lights get further from the power source.
Some factors of voltage drops are:
•Amount of wattage on the wire run
•Output from the power supply
•Wire size (commonly used as American Wire Gages (AWG)
How does voltage drop behave with different mediums or materials?
To calculate voltage drop, you need to know the wire resistance. Different material of conductor has its own resistance.
The resistance of wire depends upon four elements:
•Wire size (diameter)
The formula of voltage drop is:
Voltage drop (Vd)= current in the run (amps) x conductor resistance (ohms per 1000 ft.) x length of the run (feet)
If current in the run is 0.5A, the wire resistance (24 AWG "copper" wire @20°C) is 0.02567 (ohms/ft) and the wire length is 10 ft,
then the voltage drop (Vd) is= 0.5(A) x 0.02567(ohms/ft) x 2 x 10(ft) = 0.2567 (V).
If the input voltage from the power supply is 12V, then the voltage drop at the end of wire is 2.14% which is under 3%.
However, if the material of wire is changed to aluminum (the wire resistance of "aluminum wire" is 0.03865 (ohms/ft)@20°C), and all other conditions are the same, then the voltage drop will be 0.3865(V). It is 3.22% of 12V input voltage which is higher than using copper wire.
In conclusion,given same conditions of ambient temperature, the wire length, wire size, and the resistance of different materials plays an important role of causing voltage drop.
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