An oV (DC Bus Overvoltage) fault is triggered when the drive's DC bus voltage rises higher than the overvoltage trip point. A CDBR (Dynamic Braking) unit paired with a resistor(s), is used to help decelerate and bring the motor to a smooth stop to prevent a fault such as an oV. If an oV fault is occurring when using a CDBR unit, an issue may be present with a system component or the CDBR unit may not be sized correctly for the application. The oV fault trip point is approximately:

• 410 VDC for a 200 V class drive
• 820 VDC for a 400 V class drive
• 1040 VDC for a 600 V class drive

Follow the steps below when troubleshooting an oV (DC Bus Overvoltage) fault when using a CDBR-xxxxD Dynamic Braking Unit:

1. Verify the parameters are set correctly on the drive when using dynamic braking. Refer to document: Programming when Installing a Dynamic Braking Option.
2. With power applied to the drive, view the LEDs on the CDBR Braking Unit to ensure the braking unit is in working condition. The DISABLE LED must be OFF, the CHARGE LED must be ON and either the MASTER or SLAVE LED must also be ON.
   
    

   LED	Color	Lit	Off
   MASTER	Green	CDBR is functioning as Master	CDBR is functioning as Slave
   SLAVE	Green	CDBR is functioning as Slave	CDBR is functioning as Master
   DISABLE	Red	Fault has occurred	Normal operation
   CHARGE	Red	CDBR is powered on	-

    
3. Verify the DIP switch settings for S1 and S4.
   • DIP switch S1 is used to select SINK or SOURCE mode for the SB to SC Enable input.
     • If S1 is set to SINK (factory setting), it is using internal 24Vdc.
     • If S1 is set to SOURCE, an external 24Vdc (Class 2) power supply is required.
   • DIP switch S4 is used to select the contact type to either Normally Open (N.O.) or Normally Closed (N.C.).
     • If S4 is set to N.O. (factory setting) and the SB to SC terminals are OPEN, the Dynamic Braking unit is automatically enabled.
     • If S4 is set to N.C. and the SB to SC terminals are CLOSED, the Dynamic Braking unit must be remotely enable by a switch across terminals SB to SC.
       
        
       Refer to the table below for the DIP switches S1 and S4 details.

       DIP Switch S1 SINK/SOURCE	DIP Switch S4-SB/SC Terminals N.O./N.C.	SB-SC Enable Input	CDBR Status
       SINK	A	Open	Enabled
       SINK	A	Close	Disabled
       SINK	B	Open	Disabled
       SINK	B	Close	Enabled
       SOURCE	A	0V Input	Enabled
       SOURCE	A	24V Input	Disabled
       SOURCE	B	0V Input	Disabled
       SOURCE	B	24V Input	Enabled

        
4. Verify the DIP switch setting for S2. The default setting of DIP switch S2 is OUT (Master). Change the switch position only when operating the unit as a slave device.
   • Refer to document: Using Braking Units in a Parallel (Master-Slave) Configuration
     
      
5. Check the Braking Start Voltage rotary switch S3. Set the Voltage Activation Level rotary switch S3 to match the power supply of the main circuit. The default rotary switch S3 setting is 9.
   
    
   Refer to the table below for the S3 rotary switch position and braking start voltage details.

   Rotary Switch S3 Setting	200V Class		400V Class		600V Class
   	Input Voltage (V)	Braking Activation Voltage (V) (PN Bus Voltage)	Input Voltage (V)	Braking Activation Voltage (V) (PN Bus Voltage)	Input Voltage (V)	Braking Activation Voltage (V) (PN Bus Voltage)
   0	160	270 (TYP)	380	630 (TYP)	500	825 (TYP)
   1	170	282 (TYP)	390	644 (TYP)	505	839 (TYP)
   2	175	294 (TYP)	400	659 (TYP)	515	853 (TYP)
   3	185	307 (TYP)	405	673 (TYP)	525	867 (TYP)
   4	190	319 (TYP)	415	688 (TYP)	530	881 (TYP)
   5	200	331 (TYP)	425	702 (TYP)	540	894 (TYP)
   6	208	343 (TYP)	430	717 (TYP)	550	908 (TYP)
   7	215	356 (TYP)	440	731 (TYP)	555	922 (TYP)
   8	220	368 (TYP)	450	746 (TYP)	565	936 (TYP)
   9 <1>	230	380 (TYP)	460	760 (TYP)	575	950 (TYP)

     <1> Default setting
    
6. Check the wiring between the drive, resistor, and braking unit.
   • For smaller model drives, refer to document: Connecting a Braking Resistor or CDBR Braking Unit to a Drive (Smaller Models).
   • For larger model drives, refer to document: Connecting a Braking Resistor and CDBR Braking Unit to a Drive (Larger Models).
7. Check the braking resistor(s) following the steps below:
   1. Remove power to the drive. 
   2. Disconnect the resistor(s) from the circuit and determine the rated value (ohms) of the resistor(s) which is usually stamped or labeled on the resistor itself.
   3. Visually inspect the resistor(s) for cracks, defects, etc.
   4. Use a multimeter to measuring the resistance.
   5. Compare the resistance readings (ohms) to the value stamped on the resistor.
   6. If the resistance measured is significantly different from rated value of the resistor, replace the resistor.