Sevcon MillipaK 4QPM Manual page 57

Controller Protection Timed Current Cutback
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Timed Current Cutback
During periods of high current usage the power components of the controller produce
considerable heat. Under normal circumstances the controller will cutback the maximum current
supplied to the load when the heatsink temperature rises above a safe level for the controller
components. However, when the current supplied is close to the maximum rating of the controller
the temperature rise of the components leads the heatsink temperature by up to 40°C. If this
situation was allowed to arise damage may result in the controller. In order to prevent this
situation a timed current cutback feature is incorporated in the MillipaK controller, which works
as described below:
The controller monitors the load current each second and estimates the junction temperature of the
o
MOSFETs. If the estimated temperature exceeds 105 C, then the current limit is reduced by 1% of
o
the Armature Block Rating (ABR). If the temperature is above 80 C and the temperature has
o o
exceeded 105 C without falling below 100 C, then the current limit is reduced by 1% of the ABR.
o
If the temperature is below 80 C, then the current limit is increased by 1% of the ABR. The
current limit can be reduced to a minimum of 60% of the ABR.
The system will limit the current through the armature to the calculated limit during drive and
braking.
MillipaK 4QPM Controller Manual Page 57 13/08/03