User’s Manual
27
4. OPERATION
4.1. FUNCTIONAL DESCRIPTION
The M3452 module controls the bus voltage of a variable frequency drive by
transferring energy to a resistor.
When the drive’s DC bus voltage exceeds a fixed setpoint, the dynamic braking
transistor module’s control electronics turns on an IGBT transistor connecting a
resistive load across the DC bus. When the DC bus drops below another threshold,
the IGBT turns off. The setpoints are listed in Section 6.
The R8 version adds control and monitoring over a network connection.
4.2. FEATURES
4.2.1. INDICATORS
4.2.1.1. DC BUS
The amber DC bus indicator illuminates when the voltage between the
DC+ and DC- terminals is greater than 50VDC.
Do not use this light as an indication that the DC bus is safe to work
on! Always check the DC bus with a working voltmeter before
servicing equipment, as the DC bus light may be broken!
4.2.1.2. CONTROL POWER / FAULT
This green indicator illuminates when control power is applied to the unit.
A solid light indicates that no faults are present and the control circuit is
functioning. A flashing light indicates a fault, with the pattern of flashing
lights indicating the type of fault (see Table 4-1 in Section 4.2.5). All faults
(except Overtemp and Open Thermistor) latch until a reset signal is
applied. Overtemp and Open Thermistor will clear automatically when
the unit temperature falls to a safe level. See Section 4.2.2.4 for more
information about the reset input. The short IGBT blown fuse faults will
not reset until power-down.
Note: See Section 5 for specific faults and troubleshooting.
4.2.1.3. ACTIVE BRAKING
This red indicator illuminates when the chopper IGBT is on. When the
drive is idle, this light should not be on. During braking, this light will be
on or flashing, depending on the amount of braking energy.
This light will also be on if the Bus Discharge input is active.
4.2.2. TERMINAL STRIP I/O
4.2.2.1. V+ INPUT SUPPLY – TB2-1
This unregulated 24VDC supply can be used to drive the inputs. It is rated
at 50 mA. It should only be used for this purpose.
4.2.2.2. ENABLE INPUT – TB2-2
These terminals must be connected for the module to regulate the DC
bus.
Modules are enabled by closing a dry contact between the terminals. This
is an active high (sinking) 24V signal common to TB2-5. Both this input
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