Danfoss VLT CDS 302, Troubleshooting Manual

Static test procedures

POWER MUST BE OFF / MAINS AND MOTOR 
CABLES DISCONECTED!

Verification of: Rectifier (input, mains) / IGBT 
(Output, motor)

• 

 If rectifier or IGBT fail, the complete power 
card has to be exchanged, since in the CDS 
drives, the rectifier and IGBT are integrated in 
one power card.

Rectifier test (static)

Symptom: 

Step 1

Figure 12: Multimeter 

should read a voltage drop 

of 0,4V

Figure 13: Multimeter 

should show diode open

Figure 14: Multimeter 

should show a diode drop 

of 0,44V

Step 2

Step 3

Failure of the rectifier module will usually result 
in blown input line fuses.

Procedure to conduct the static test on rectifier:

•  Connect the negative terminal of the 

multimeter meter lead to the positive DC bus.

•  Connect the positive terminal of the multimeter 

lead to the input terminal L1,L2,L3 in turn.

•

   The multimeter should show the diode drop 

of around 0.44 volt on the three terminals.

Now reverse the meter leads,  i.e. connect 
the positive terminal of the meter lead to the 
positive DC bus.

•  Connect the negative terminal of the meter 

lead to the input terminals L1, L2, L3 in turn.

• 

The multimeter should show diode open.

Now repeat the procedure by connecting to 

the 

negative DC bus

 in order to the test the lower 

part of the rectifier bridge which consist of 
diodes

•  Connect the negative terminal of the meter 

lead to the input terminals L1, L2, L3 in turn.

•  

The multimeter should show the diode drop 
of around 0.44 volt on the three terminals.

14

FRCC.PC.036.A2.02

Check List