Installation Guide

Danfoss Drive PM.doc Page 3 of 3
d. With power removed from the drive, a physical inspection of the capacitors should not show
any deformation of the cases of the capacitors or liquid leaking from them.
e. Low voltage capacitor testers are of no use in checking DC bus capacitors. The main
concern is to ensure that the capacitors don’t have excessive leakage current when the DC
bus voltage is applied to it. This cannot be tested at a low voltage.
f. If one capacitor on the DC bus is found to be weak or damaged, it is important to replace the
entire capacitor bank. A capacitor with an excessive amount of leakage current places
excessive stress on other capacitors in the bank.
g. If it is convenient to access the two halves of the DC bus capacitors, the inspection
technique given in “c” and “d” can be performed annually. Otherwise, it is best to simply let
the drive’s internal monitoring circuitry described in “b” provide an indication of possible
problems.