3.2.2 Service life and temperature. Osram HQI-E 150 W/NDL CL
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U
ECG
S
Fig. 13: Simplified circuit diagram showing the electronic operation of high intensity discharge lamps
Voltage in V
Luminaire
Lamp
Current in A ture which can be measured by a thermocouple at a set point – the t c
point – and is defined as maximum permissible temperature at which safe operation of the electronic ballast is still guaranteed. In addition, the t c temperature is set in relation to the ballast service life.
That means that the measured t c temperature permits very precise conclusions as to the anticipated service life of the electronic ballast.
OSRAM’s HID electronic ballast for example principally reaches its full nominal service life at the maximum permitted t c
temperature. In practice, this means that any temperature levels below the t c temperature always prolong the effective service life. As a rule of thumb, it can be presumed that a temperature 10 °C below the printed maximum t c
temperature will double the service life of the electronic ballast.
Time in ms
Fig. 14: Current and voltage of a metal halide lamp operated on a rectangular electronic ballast
For a conventional ballast, it can be presumed that the service life is defined by the choke temperature t w
. A
10 °C increase in the t w temperature means that the service life is halved.
However, it is not advisable to use only the absolute maximum tolerable t c value for conclusions regarding the quality and service life of an electronic ballast. This is because on the one hand, the position and therefore indirectly also the value of the t c point can be freely defined by every electronic ballast manufacturer. On the other hand, the rule of stating the nominal service life at the maximum permitted t c temperature has not yet become established throughout the electronic ballast industry. In practice this means that many electronic ballasts only achieve approx. 50% of their nominal service life at maximum t c
temperature.
In electronic ballasts, these circumstances are far more complicated. The mortality rate of individual components, the circuit design and above all the electronic load and the temperatures at which the units are operated have a considerable influence on the service life behavior.
Nominal service life (B10): max. 10% of the electronic ballasts have failed
A serious evaluation of the electronic ballast service life is only possible by comparing the electronic ballast ambient temperature t a
with the corresponding service life.
Comparison of the service life using only the t c temperature is not appropriate.
This is why the nominal service life of electronic ballasts is stated in combination with a failure probability. For example, all units in the product family
POWERTRONIC ® PTi have a nominal service life of
40,000 hours with failure probability of maximum
10% when operated at the maximum permissible temperatures.
3.2.3 Advantages of operation with electronic ballast POWERTRONIC ® PTi
The service life of electronic ballasts is influenced directly by the temperature at which the units are operated. This is why 2 temperature values are defined to describe the thermal behavior. The ambient temperature t a describes the temperature immediately surrounding the unit and thus prevailing around the electronic components. To be clear, this is not the room temperature or the ambient temperature of the luminaire.
The following table provides an overview of the advantages of operating lamps with the electronic ballast.
The corresponding values and statements are based on tests and experience with POWERTRONIC ® PTi ballasts, so that they cannot necessarily be transferred
1:1 to ballasts of other makes.
In comparing the conventional and the electronic ballast, the performance of the conventional ballast constitutes the reference parameter and is given a value of 100. This is also based on the fact that the lamp parameters are defined with the reference conventional ballast.
When an electronic ballast is fitted in a luminaire, the real ambient temperature t a of the ballast can only be measured with great difficulty and at great effort. This is why a second temperature has been stipulated: the t c
temperature. Basically this is the casing tempera-
For more details, please refer to the POWERTRONIC
Technical Guide – Electronic control gears for metal halide lamps.
®
13
14
Magnetic ballast Electronic ballast POWERTRONIC ®
Energy consumption
Lamp service life
Lamp start-up
Colour stability
Cut-out at end of lamp service life
Ignition cut-out
Light flicker
Consistent wattage
100
100
10 to 15% savings over the service life
Up to 30% longer depending on lamp type and kind of use
Depends on type: usually approx.
60 to 90 sec. to reach 90% of the luminous flux level
Up to 50% faster
Colour variation possible Clearly reduced scattering; initial and over service life
Not available or only simple cut-out mechanisms
Permanent parameter control, intelligent cut-out mechanisms
Only with timer ignition units
Visible flicker
Increase in wattage over service life, also dependent on fluctuations in temperature and supply voltage, and on lead length
Ignition time limited to 18 min
Flicker-free thanks to 165 Hz operation
+ 3% over the entire service life, regardless of fluctuations in temperature and supply voltage or lead length
Handling
Size and weight
Power factor correction (PFC)
Noise development
Bidirectional data exchange
3 components, complicated wiring
1 unit, simple wiring
Heavy, several components, large in some cases
Light and compact
0.5 – 0.95, considerable aging fluctuations
> 0.95
Clearly audible humming possible Almost noiseless
Not possible Generally possible
The main advantages of electronic ballasts are described in greater detail in the following section.
3.2.3.1 Reducing energy consumption
By contrast, electronic ballasts operate the lamps always with constant wattage throughout the entire service life. The maximal tolerated fluctuation is 3%. This means for example that for a 70 W ceramic arc tube lamp, the electronic ballast constantly provides the lamp with the rated 73 W.
Compared to conventional ballasts, electronic ballasts can considerably reduce energy consumption over the service life. The energy savings result from two factors:
1) Unit power dissipation:
In conventional ballasts a large amount of energy is lost in dissipated heat on account of the design. By contrast, electronic ballasts have a low-loss design with top quality components, reducing dissipation to less than 10% of the nominal power.
3.2.3.2 Lamp service life and cut-out at the end of the service life
A detailed description of the lamp service life and failure behavior using conventional ballasts can be found in chapter 6.
2) Increase in wattage over service life:
The system wattage with conventional ballasts fl uctuates signifi cantly over the service life of the lamp. This results from the change in lamp voltage, which can increase by up to 30% throughout the service life (see also chapter 3.1.2), resulting in considerable fl uctuations in lamp wattage.
Electronic ballast operation also offers considerable advantages in terms of lamp service life and cut-out behavior at the end of the service life.
Comprehensive laboratory tests and extensive practical experience show that operation on electronic ballasts has a significantly positive influence on the lamp service life. Precise but gentle lamp ignition, a more stable thermal balance thanks to constant wattage
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