Parker Hannifin 88-021610-01G - Manual (Page 182)

Parker Hannifin
182 Aries User Guide
Peak Dissipation
During a single deceleration, all the calculated power-dump energy (E
R
) must
dissipate in the external resistor. The external power-dump resistor then
slowly dissipates that energy as heat. This peak power must not exceed the
capabilities of the resistor, which is typically 10 times the average power
rating.
D
R
PEAK
t
E
P
=
Where
P
PEAK
= peak power into the external power dump resistor (Watts)
E
R
= energy to be dissipated in the external resistor (Joules)
t
D
= deceleration time (Seconds)
Average Dissipation
Repetitive moves need to dump the energy each time the deceleration
occurs. The duty cycle of this repetition determines the average power the
resistor must dissipate. This average power must not exceed the capabilities
of the resistor.
Power resistors are rated based on ideal heatsink and airflow conditions, and
are therefore often over-rated by the manufacturers. To ensure the average
energy dissipation of the resistor exceeds the average power dump for the
application, the regenerative power should never exceed 50% of the
resistor’s average power rating.
C
D
PEAK AVG
t
t
P P
⋅ =
Where
P
AVG
= average power into the external power dump resistor (Watts)
P
PEAK
= peak power into the external power dump resistor (Watts)
t
D
= deceleration time (Seconds)
t
C
= cycle time or time between each deceleration event (Seconds)
Important — Under normal operation the external power-dump resistor
could operate in excess of 200 °C. Keep the resistor away from thermally
sensitive components, such as cables or plastic hardware.
Proper installation may require the use of thermal compound and proper
thermal connection to a heat absorbing metal surface.