1.
2.
3.
4.
5.
1.
2.
3.
4.
-
10.2 Reforming the Capacitors
The electrolytic capacitors in the DC link rely on a chemical process to provide the insulator between the two metal plates. This
process can degrade over a period of years when the drive has been non-operational (stocked). The result is that the working volt-
age of the DC link gradually falls.
The correct course of action is to ensure that the insulation layer of the capacitor is ‘reformed’ by the application of a limited current
using a DC supply. Current limiting ensures that the heat generated within the capacitor is kept at a sufficiently low level to prevent
any damage.
D A N G E R
SHOCK HAZARD FROM CAPACITORS
The capacitors can be charged even when disconnected. Contact with this voltage can lead to death or serious injury.
If the AC drive or spare capacitors are intended to be stocked, discharge the capacitors before storage. Use a measuring de-
vice to make sure that there is no voltage. If in doubt, contact your Danfoss Drives representative.
Case 1: AC drive which has been non-operational or stocked for over 2 years.
Connect the DC supply to L1 and L2
or
the B+/B terminals (DC+ to B+, DC- to B-) of the DC link or directly to the capacitor
terminals. In the NX AC drives with no B+/B- terminals (FR8–FR9/FI8–FI9), connect the DC supply between 2 input phases
(L1 and L2).
Set the current limit maximum to 800 mA.
Slowly increase the DC voltage to the nominal DC voltage level of the AC drive (1.35 x U
n
AC).
Start to reform the capacitors.
The time of reforming depends on the time of storage. See
0
1
2
3
4
5
6
7
8
9
0
1
3
5
7
2
4
6
8
9
C
B
A
e3
0b
h4
87
.1
0
Illustration 52: Storage Time and Reforming Time
A
Storage time (years)
B
Reforming time (hours)
C
Reforming time
After the reforming operation is done, discharge the capacitors.
Case 2: Spare capacitor which has been stocked for over 2 years.
Connect the DC supply to DC+/DC- terminals.
Set the current limit maximum to 800 mA.
Slowly increase the DC voltage to the capacitor nominal voltage level. See information from component or service docu-
mentation.
Start to reform the capacitors.
The time of reforming depends on the time of storage. See
AQ275638903263en-000601 / DPD00910
126 | Danfoss A/S © 2022.12
Maintenance
VACON® NXS/NXP Air-cooled
Operating Guide
