Rockwell Automation MDF-SB1304F Kinetix 6000M Integrated Drive-Motor System - Manual (Page 133)

Rockwell Automation Publication 2094-UM003A-EN-P - May 2012 133
Kinetix 6000M System Sizing Appendix D
Example
The equations in step 3 are applied to augment the table from the previous step
(shown below). The estimate of the voltage assuming all IDM units are at the end
of the total cable length is included in the last column.
This illustrates how the 32V average voltage estimate is a poor choice for this
system configuration. Using 32V as the applied IDM unit voltage for the load
current calculation results in a calculated voltage at end of the total cable length
of 36V, so the 32V estimate is obviously too small. Using 37V as the applied IDM
unit voltage for the load current calculation results in a calculated voltage at the
end of the total cable length of 36.8V. Therefore 37V is close to the best possible
value and a load current value of 2.64 A will be used for the remainder of this
example. The total IDM unit load current as a percentage is 2.64/6.5 = 40.6%.
The voltage at the end of the total cable length is greater than the minimum
voltage specification for the IDM unit, so this is a valid system configuration.
Using a more sophisticated model, the IDM unit control power load current was
calculated to be 2.42 A and the voltage at the last IDM unit to be 40.15V. The
total IDM unit control power usage was 103 W, compared to 97.5 W calculated
in step 1. The additional 5.5 W are losses in the hybrid cable. This illustrates how
using the simplified system for sizing overestimates the total IDM unit control
power current and the voltage drop along the hybrid cable.
Table 24 and Table 25 show the maximum cable length per IPIM module using
Motion Analyzer.
The following is assumed:
• All IDM units are MDF-SB1304 (highest brake load).
• Cable length is identical between all IDM units.
• Minimum cable length is1 m (3.3 ft).
• Every other IDM unit includes a brake, starting with #2.
• When the number of brake IDM units are greater than 1/2 the total units,
they are placed at the end of the daisy chain.
Average IDM Unit Control
Power Voltage Estimate
(VDC)
IDM Unit Control Power Load
Current
(A)
Voltage Estimate at Last (all) IDM
Unit(s)
32 3.05 36.0
37 2.64 36.8
42 2.32 37.4
IMPORTANT When using the simplified system to calculate cable length, the resulting
maximum cable lengths will be much shorter.