The motor ratings or nominal motor currents specified or recommended on the datasheets for the use of a braking device refer to normal applications with drives having a moment of inertia that approximately equals the moment of inertia of the motor.
\nIn all other cases, the required braking torque or braking current need to be determined more precisely (see below).<\/p>\n
Without taking into account any possible braking torques of the load, the required braking current (direct current) can be estimated according to the following formula:<\/p>\n
IB\tBraking current in A
\nfB\tBraking factor acc. to the table specified below
\ntB\tBraking time required in s
\nIN\tNominal\/rated motor current in A
\ntA\tTime until nominal speed is reached (in the case of motors with star-delta
\nstart \u2013 approx. switch-over time)<\/p>\n
IB=fB\u00d7\u221a(tA\/tB)\u00d7I N<\/p>\n
Values usual for tA:
\nConveyor belt - 20s\t\tPump - 8s\t\tPower crusher - 30s
\nCompressor - 10s\t\tFan - 20s\t\tCircular saw - 10s<\/p>\n
The following example is to explain the calculation:<\/p>\n
Example 1
\nAssumption:
\nMotor shaft power:\t\t\t\t\t\t2.2kW (230V\/400V)
\nNominal motor current (2-pole motor):\t8.5A\/4.9A
\nRamp-up time (circular saw):\t\t\t6s (direct start)
\nBraking frequency:\t\t\t\t\t\t1\/h<\/p>\n
The application of the circular saw requires that, after switching the saw off, the saw disk must come to a standstill within 5s.
\nFrom this, there results a maximum braking time of 5s which we use in the calculation formula, too:<\/p>\n
16,1A =3\u00d7\u221a(6s\/5s)\u00d74,9A<\/p>\n
In the case of this application with direct start, the motor windings are in nominal operation star-connected. Braking too is effected in star-connection, which results in a braking current of approx. 16A (fB \u2013 3), i.e, for this circular saw, a braking device with a nominal\/rated current of at least 20A, such as a VB 400-25L or VB 400-25 (with a max. braking current of 25A each), has to be used.<\/p>\n
A very importand aspect in the dimensional calculation of brakes is to take into account the cyclic duration factor (c.d.f.) indicated on the data sheets. Under no circumstances the c.d.f. be exceeded (the worst case is to be taken into account!).<\/p>\n
How to calculate the cyclic duration factor (c.d.f.): <\/p>\n
tB\tBraking time
\ntZ \tCycle time (running - braking)<\/p>\n
c.d.f =tB\/tZ\u00d7100<\/p>\n
If the required cyclic duration factor (c.d.f.) exceeds the permissible values indicated on the data sheet, the permissible maximum braking current is to be accordingly reduced.<\/p>\n
The data required in this connection can be found in the device-specific commissioning instructions.
\nIf it is not possible to reduce the braking current, a braking device with a higher braking current has to be used.<\/p>\n
Example:
\nIf the required c.d.f. is twice as high as the value indicated on the data sheet, a braking device of twice the nominal\/rated device current has to be used.<\/p>\n","protected":false},"excerpt":{"rendered":"
The motor ratings or nominal motor currents specified or recommended on the datasheets for the use of a braking device refer to normal applications with drives having a moment of inertia that approximately equals the moment of inertia of the motor. In all other cases, the required braking torque or braking current need to be […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":211,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-9375","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"\n