Danfoss FC 300 Design Manual page 48

3. Introduction to FC 300
Danfoss recommends the brake resistance R
quency drive is able to brake at the highest braking torque (M
written as:
R
rec
3
η
motor
η
VLT
For 200 V, 480 V, 500 V and 600 V adjustable frequency drives, R
written as:
V
200
V
480
V
500
V
600
V
690
1) For FC 300 adjustable frequency drives ≤ 7.5 kW shaft output
2) For FC 300 adjustable frequency drives > 7.5 kW shaft output
3.7.2. Control with Brake Function
The brake is to limit the voltage in the intermediate circuit when the motor acts as a generator.
This occurs, for example, when the load drives the motor and the power accumulates on the DC
link. The brake is built up as a chopper circuit with the connection of an external brake resistor.
48
2
U x
dc
Ω =
P x M x
motor br
(%)
is typically at 0.90
is typically at 0.98
107780
R
: = Ω
rec
P
motor
375300
R
: = Ω 1)
rec
P
motor
464923
R
: = Ω
rec
P
motor
630137
R
: = Ω
rec
P
motor
832664
R
: = Ω
rec
P
motor
NOTE
The resistor brake circuit resistance selected should not be higher than that recom-
mended by Danfoss. If a brake resistor with a higher ohmic value is selected, the
160% braking torque may not be achieved because there is a risk that the adjustable
frequency drive cuts out for safety reasons.
NOTE
If a short circuit in the brake transistor occurs, power dissipation in the brake resistor
is only prevented by using a line switch or contactor to disconnect the AC line for
the adjustable frequency drive. (The contactor can be controlled by the adjustable
frequency drive).
NOTE
Do not touch the brake resistor, as it can get very hot during/after braking.
MG.33.B9.22 - VLT
, i.e., one that guarantees that the adjustable fre-
rec
100
x
η η
VLT motor
V R
480 :
® is a registered Danfoss trademark.
FC 300 Design Guide
) of 160%. The formula can be
br(%)
at 160% braking torque is
rec
428914
= Ω 2)
rec
P
motor