TM 5-3895-374-24-1
Recommendations for use
of the motor/speed controller combination
Thermal protection
Indirect protection of the motor is incorporated in the speed controller, taking into account
of the motor
- the current absorbed by the motor,
- the motor speed (ventilation),
- an ambient air temperature of 40?C.
See tripping curves on the left.
For adjusting And monitoring of the thermal
state of the motor, see p. 49.
To provide direct thermal protection, use PTC thermistor probes embedded in the motor
windings, associated with an LT2-S protection relay, for operation in severe ambient
conditions :
- high ambient temperature (0 > 40°C),
- risk of cooling fins clogging,
- insufficient ventilation
Intermittent duty
The amount of starting and braking is limited by the value of the overloads, their duration, as
well as the load during normal running and the motor cooling possibilities.
On intermittent duty, the current which causes the motor and speed controller to overheat
appears as follows:
IM: overload current
In: rated current
Im normal runnning current
The following curves can be used to determine the ratio between the overload duration and
the operating time at 0,8 of the rated current at rated speed
EXAMPLE following an overload of
1,3 in for 10 seconds, it would require
20 seconds at 0,8 in to return to the
previous thermal state
If the normal running speed is lower than
the rated speed, time t2 will be longer
(page 3-181)
