SK 500E – Users Manual for Frequency Inverters
44
BU 0500 EN-3021
2.6.6 Monitoring of the brake resistor
To prevent overload of the brake resistor, it should be monitored during operation. The most reliable
method is thermal monitoring with a temperature switch which is mounted directly on the brake
resistor.
2.6.6.1
Monitoring with a temperature switch
Type SK BR2-… brake resistors are equipped with a suitable temperature switch as standard; suitable
temperature switches are available as options for types SK BR4-… (please see chapter 2.6.1
"Electrical data for brake resistors"). If the bottom-mounted brake resistor is mounted below the
frequency inverter
(SK BR4
-
…)
it must be noted that a temperature switch with a
reduced switching
threshold (100°C)
must be used.
Typically, evaluation of the temperature switch is carried out by an external control system.
Alternatively, the temperature switch can be evaluated directly by the frequency inverter. To do this, it
must be connected to a free digital input. This digital input must be parameterised with the function
{10} "Block voltage".
Example, SK 520E
• Connect the temperature switch to digital input
4 (Terminal 42 / 24)
• Parameterise P423 to function {10} "Block
voltage"
The switch opens if the maximum permissible
temperature of the brake resistor is reached. The
output of the frequency inverter is blocked. The
motor runs down to a standstill.
21
22
23
24
25
42
40
41
15V
motor - PTC
2.6.6.2
Monitoring with current measurement and calculation
As an alternative to monitoring with a temperature switch it is also possible to use an indirect,
arithmetical monitoring of the the brake resistor load on the basis of measurement values.
This software-assisted indirect monitoring is activated by setting parameter (P556) "Brake resistor"
and (P557) "Brake resistor power". The actual calculated brake resistor load can be read out in
parameter (P737) "Brake resistor load". Overload of the brake resistor results in a shut-down of the
frequency inverter with the error message E3.1 "Overcurrent Chopper I²t“
NOTICE
Overload of the brake resistor
The supported indirect monitoring using measurement of electrical data and calculation is based on standard
ambient conditions. In addition, the calculated values are reset when the device is switched off. It is therefore not
possible to detect the actual load on the brake resistor.
It is therefore possible that an overload may not be detected or its environment may be damaged due to excess
temperatures.
Reliable temperature monitoring is only possible with the use of a temperature switch.
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