The lifetime of an individual component is mainly dependent upon the quality of the materials used. This of course has an impact on the manufacturing cost of the device.
In order to control the failure rate of complete ballast, the method of calculating the Mean Time Between Failures should be adopted. This takes into account the MTBF of all the components. The Failure Rate (FR) is 1 divided by the MTBF. Temperature within the luminaire has one of the biggest impacts on the life expectancy so the positioning of the ballast is critical and the ballast manufacturers generally use 65°C for calculation at a pre-defined point on the ballast enclosure (tc point). The quality of the design and the components must result in a certain specified calculated failure rate. For most electronic ballasts this is set to 1% at 5,000 hours. According to the equation:
Rt = e-λt or 1n Rt = -λt
Where Rt is the remaining number of ballasts after the time t and λ is the failure rate of 1% per 5,000 hours = 0.20 .10-5, it is found that 36.7% of ballasts are still operational after 500,000 hours or 50% after 346,000 hours. The 10% failure rate is reached after 52,680 hours.
From a maintenance point of view this means that in a commercial light control installation of 100 ballasts it would be reasonable to expect 1 to fail each 5,000 hours until 50,000 hours when 10 would have failed. The rate would then accelerate.
These figures apply to HF ballasts, both dimming and switching. As with any electronic device, the more complicated then the higher the risk of failure.
1. A DALI ballast is the most complicated as it is individually addressed and configured.
2. A DSI ballast is next as it is digitally controlled but not addressed or configured but does have bi-directional communication.
3. A 1-10V ballast is the simplest form of fluorescent dimming as it is switched on and off by applying mains power and dimmed by a 1-10V DC voltage
4. A HF non-dimming ballast is the most basic form
DALI –v– DSI
DALI is the simplest to install but the longest to commission. All design and commission must be done on site after installation and each ballast must but be individually programmed. In a commercial lighting installation this can take up to ten times longer to commission than a DSI installation. DALI components are grouped up to 64 devices per group. When a ballast needs to be added/replaced it is necessary to re-commission the entire line. It would not be unreasonable for a replaced luminaire to take four or five hours to re-commission. Also, the failure rate on DALI will be the highest as being the most complicated. Therefore the high cost of maintenance must be considered when installing DALI in a commercial light control installation.
DSI is controlled in groups normally from a Light Control Module (LCM) in a commercial light control installation and has the same functionality as DALI but provided from the LCM. These ballasts are traditionally more reliable and perform well. Lamp failure and running times are still available. New ballasts can be added/replaced without the need for re-commissioning of the LCM. LCM’s can be pre-commissioned prior to installation dramatically reducing commissioning time and reducing and simplifying the system.
For Further Information Contact:
Pammvi Group of Companies
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Pammvi is sole distributor and dealer of Steinel, Germany products for lighting automation and power tools in India, Bangladesh, Sri Lanka and other sub-continent countries. Pammvi also deals in FDA certified drugs of abuse test kits and AED.