ABB i-bus KNX Product Manual page 246

ABB i-bus® KNX PLANNING AND APPLICATION
12 Planning and application
12.1 Introduction
This chapter includes some tips and application examples for practical use of the device.
12.2 Ballast calculation
The ballast unit is used to operate gas-discharge lamps, e.g. fluorescent lamps. It converts the main volt-
age to the optimal operating voltage for the gas-discharge lamp and allows the gas-discharge lamps to
be ignited (switched on). Lamps ignite with a time offset in choke/starter circuits; all fluorescent lamps
ignite nearly simultaneously in ballast circuits.
With LED lamps, the ballast unit is referred to as an LED driver or LED converter. The LED driver provides
constant direct current or smoothed direct current for operating the connected lamps (LEDs).
Input capacitors in the electronic circuit of the ballast unit are required for storing charge to rectify and
stabilize the alternating voltage or current on the primary side. The input capacitors charge at the mo-
ment of switch-on, briefly resulting in a very high inrush current. If several ballast units are used in the
same circuit, simultaneous charging of the capacitors can cause very high inrush currents to flow. This
peak inrush current I
the back-up fuse.
The ballast unit's inrush current depends not only on the wattage, but also on the type, the number of el-
ements (lamps) and the manufacturer. The specified maximum number of ballast units that can be con-
nected per output is therefore only a guide value.
To determine the maximum number of ballast units that can be connected per output, the peak inrush
current I
of the ballast unit for this information.
Typical peak inrush current I
• single-element ballast units with T5/T8 fluorescent lamps: 15 ... 50 A, pulse time 120 ... 200 µs
• LED drivers: 3 ... 50 A, pulse time 40 ... 250 µs
Refer to the device's technical data → Product overview, Page 10 for the maximum peak inrush current I
of the switching outputs.
Example:
Sample calculation for determining the maximum number of connectible ballast units per output:
• ABB i-bus® KNX ballast 1 x 58 CF, maximum peak inrush current I
• Maximum permissible peak inrush current I
200 A / 33.9 A = 5.89
Max. five ballast units can be connected.
must be taken into account when designing the switching contacts and selecting
p
and the associated pulse width of the ballast unit must be known. Refer to the technical data
p
values for
p
= 33.9 A (147.1 µs)
p
of the output: 200 A
p
Product manual | SAH/S x.x.7.1 | 2CDC505173D0211 Rev. A 246
p