MTS Systems MPA-05-460, Manual

Page: 33 / 45

33
Shunt Loads
Regenerative energy during deceleration causes the normal voltage on the drives bus to
increase. The amount of energy is application dependent and relates to total inertia. In
general the drives internal shunt load can dissipate this energy within the constraint that
the load inertia is not more than 20 times that of the rotor but, this is a guideline. The
deceleration rate of the load determines the rate that voltage rises in the bus capacitors.
The voltage on the bus is sensed and when it becomes too high a solid state device turns
on that causes a load to be placed in parallel with the bus. There are three protection
devices that are used to protect the drive from this application dependent loading. The
shunt loads are thermally protected to 85° maximum, there is a fuse in series with the
shunt load to limit average power in the shunt and if this fuse blows then another circuit
measures the bus for an even higher voltage and a HI-BUS fault occurs and disables the
drive.
For 460 volt drive products, the shunt is turned on at 780 Vdc and turns off at 750 Vdc. A
HI-BUS fault occurs if the bus goes over 860 Vdc.
Model Load ohms Fuse amps Peak amps Bus Capacitors
MFD (min) Continuous
Watts
MPA-05-460 48 4 16.2 600 400
MPA-09-460 48 4 16.2 1100 400
MPA-15-460 48 8 16.2 1700 800
MPA-25-460 26 10 30.0 1600 1500
MPA-35-460 26 10 30.0 2200 1500
MPA-50-460 16 20 48.7 3300 2000
MPA-75-460 16 20 48.7 5000 2000
MPA-100-460 16 20 48.7 6800 2000
External Shunt Load
Model Load ohms Fuse amps Peak amps Bus Capacitors
MFD (min) Continuous
Watts
EXS-50-460 16 25 49 – 2400
EXS-100-460 8.3 45 90 – 8000