T 7 Operation
7.4 Swith-on frequeny
Switch-on frequency is accordant to the time between two consecutive switch-ON operations. This time
interval may not be selected arbitrarily, because each switch-ON operation is combined with a thermic load
of the precharge resistors.
The purpose of the precharge resistors is to limit power on current when connecting in mains voltage. Due to
space limitation, NTC resistors are used, packaging temperature of which increases during the precharge of
the DC link electrolytic capacitors. If the DC link voltage has exceeded an adjustable threshold, the resistors
are short connected by the precharge relay and can cool down again to environmental temperature.
NOTE
Between two consecutive switch-on events there have to be passed at least three minutes. If
time to cool down is shorter than necessary (about 100s), this can result in a thermic overload
and destruction of the precharging resistors.
The time between switching off the device and switching it on again is irrelevant in this context,
if the time the device lasts in switched-on state is greater than three minutes.
Due to different valid supply voltages at the b maXX® BM3400 the threshold for the ending of precharge can
be set via a parameter in opposition to the b maXX® BM4400. If the voltage value was selected small enough,
you can avoid, that the precharge circuit can be ac tivated again.
CAUTION
The following can occur, if you disregard this warning instruction:
• Damage to property
The danger is: electricity. If the threshold voltage you have assigned is too s mall, the precharging
circuit can be set ineffective.
• Change the default values of 75% of the supply voltage only in well-founded situations.
• Consider that a threshold value, which is too small causes a great starting current, which
can cause damages at the installation (fuse) as well as at the device (input rectifier).
114
Instrution Manual
b maXX
®
BM3400
from 206 Doument No.: 5.07013.03
Baumueller Kamenz GmbH
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