Power on switching frequency / DC link charging
Instruction handbook
b maXX
BM5500, BM5600, BM5700
Document No.: 5.13008.10
Baumüller Nürnberg GmbH
220
8.2
8.2.3
Calculation of the maximum permitted external capacitance
If a maximum allowable external capacitance is specified in the technical characteristics,
then it is either a device with diode rectification or one with the „old“ charge circuit (time
controlled charging). If, however, it is referred on this chapter the maximum external DC
link capacitance is calculated as followed prescribed.
The time for a charge sequence depends on the height of the charging current pulses and
also the height of the internal and external capacitance (refer to
on page 221). After 20 seconds the charging is discontinued.
For the charging function the device must be connected to a power supply with clockwise
rotating field. No charging is started in case of counterclockwise rotating field. In rare cas-
es a counterclockwise rotating field can cause an abrupt charging and a tripped fuse.
No charging is started at failure of one or two mains phases.
The external chargeable capacitance is not limited because the height of the loading cur-
rent of the DC link capacitor is approx. constant. But the time until the complete charge
of the DC link is increased proportional to the capacitance, that has to be charged. Error
089 („power unit not ready-to-operate“ is generated if the charging is not finished after
20 s.
Example: BM5543 on 480 V.
on page 221 results a charge time of 0.4 s with the built
in capacitance of 1880 µF.
It is recommended to choose the external capacitance 20 % lower, because the charging
time can vary depending on the height of the power supply voltage.
Maximum external capacity
built in capacity
20s
Charging time according table
------------------------------------------------------------------------------- 1
–
=
1880µF
20s
0.4
s
------------ 1
–
92mF
=
=