Observe the maximum permissible
duty cycle and the maximum switching rate of the hoist and the travel drives.
The motors on the crane are not designed for continuous operation. They must have break intervals for cooling down.
Normally, an individual motor on a crane (e.g. the motor on the trolley drive) is not operated continually over a lengthier period, but rather only briefly with corresponding break intervals (in which then, for example, the crane travel drive is operated). This operating mode is called intermittent duty.
How long an individual motor should be operated and how long the breaks for cooling down must be is determined by the duty cycle.
The duty cycle of the hoist drive and travel drive can be found in the test log book of the crane or in the section “Technical data” in the production manual of the respective hoist drive or travel drive. The values can also be taken from this table.
Observe the maximum permissible
duty cycle and the maximum switching rate of the hoist and the travel drives.
|
Total duty cycle |
Duty cycle at slow travel speed |
Duty cycle at fast travel speed |
|
25 % 2.5 min |
0.8 min |
1.7 min |
|
30 % 3 min |
1 min |
2 min |
|
40 % 4 min |
1.3 min |
2.7 min |
|
50 % 5 min |
1.7 min |
3.3 min |
|
60 % 6 min |
2 min |
4 min |
Note
The specified values (percentage and minutes) refer to a duration of 10 minutes. Example: A duty cycle of 40% means that the motor may run for a maximum of 4 minutes and must remain stationary for 6 minutes within any 10-minute period.
Furthermore, the total duty cycle is divided into 1/3 of the duty cycle at low speed and 2/3 of the duty cycle at high speed.
|
Total switching rate |
Switching rate at slow travel speed |
Switching rate at fast travel speed |
|
150 c/h |
100 c/h |
50 c/h |
|
180 c/h |
120 c/h |
60 c/h |
|
240 c/h |
160 c/h |
80 c/h |
|
300 c/h |
200 c/h |
100 c/h |
|
360 c/h |
240 c/h |
120 c/h |
Note
The values are given in switches per hour. Example: 240 switches per hour means that the motor may switch up to a maximum of 240 times within one hour.
Furthermore, the total maximum switching rate is divided into 2/3 of the switches at low speed and 1/3 of the switches at high speed.
In special situations, a motor may need to run continuously for a longer period than allowed in intermittent duty (e.g. for a long crane run or if a longer hook path must be travelled). In these cases, the motor can be run in short term duty.
The motor may only be run up to the maximum period given in the table. The motor must then be allowed to cool down.
Short term duty cycle:
|
Duty cycle in intermittent duty (see previous table) |
Corresponding duty cycle in short term duty for slow travel speed |
Corresponding duty cycle in short term duty for fast travel speed |
|
25 % |
5 min |
10 min |
|
30 % |
5 min |
10 min |
|
40 % |
10 min |
20 min |
|
50 % |
10 min |
20 min |
|
60 % |
20 min |
40 min |
Table: Duty cycle in intermittent duty and the corresponding duty cycle if the motor is operated in short term duty.
Note
Likewise in short term duty, the total duty cycle is divided into 1/3 of the duty cycle at low speed and 2/3 of the duty cycle at high speed.
Operating the drive in short term duty:
If the crane was previously just
used: Wait until the motor has cooled down to the ambient temperature.
Only run the motor at low and
high speed maximally as specified in the table.
In short term duty, the motor may not be switched on more than 10 times.
Wait until the motor has cooled
down to the ambient temperature.
Then run the motor again in
either short term duty or intermittent duty.