15
VLT
®
3500 HVAC
MG.35.B1.02 – VLT is a registered Danfoss trademark
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VLT type
3502 - 3511 HVAC, 380 V
3502 - 3504 HVAC, 200 V
3502 - 3511 HVAC, 380/500 V
2.4 Electrical installation
VLT type
3575 - 3800 HVAC, 380/500 V
3542 - 3562 HVAC, 230 V
VLT type
3516 - 3562 HVAC, 380/500 V
3508 - 3532 HVAC, 200 V
Parallel connection of motors
VLT 3500 HVAC can control several motors connec-
ted in parallel. If the motor speeds are to be different,
motors of different rated speeds must be used. The
speed of the motors changes simultaneously, which
means that the ratio between the rated motor speeds
is maintained over the whole range.
The total current consumption by the motors must
not exceed the maximum rated output current (I
VLT,N
)
for VLT 3500 HVAC.
Problems may arise at the start and at low rpm values
if the motor sizes deviate considerably. This is be-
cause small motors have a relatively high ohmic resis-
tance in the stator, which is why they require a higher
voltage during start and at low rpm values.
In systems with parallel motor operation, the internal,
thermal protection cannot be used as motor protec-
tion of the individual motor, since the output current
must be programmed to match the overall motor
current. Consequently, additional motor protection is
required, such as thermistors in every motor (or
individual, thermal relays).
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