Rockwell Automation 8720MC 8720MC Regenerative Power Supply User Manual - Manual (Page 47)

4-9 Wiring
When Model 8720MC-RPS027 and 8720MC-RPS065 are adapted
to Capacitors having large capacity
8720MC-RPS027 and 8720MC-RPS065 units charge to capacitors
with a single phase, full-wave rectification circuit through the
built-in precharge/discharge resistor. When the load capacitors
have large capacitance, it takes more time for charging, and the
wattage of the internal resistor becomes insufficient. When the
load capacitance is large, disable the built-in precharge/discharge
resistor and connect an external resistor or external circuit for
precharging/discharging (Note that minimum precharging/
discharging cycle is 3 minutes).
Calculate the rated wattage of the external precharge/discharge
resistor to be connected to the outside in accordance with the
following formula depending on the total capacitance of all the
capacitors including the built-in capacitor.
Rated wattage [W] = 17000 x C[F]
But, serge resistivity of J[J] = 28000 x C[F] must be provided.
When an external precharge/discharge resistor is connected
between PR1 and PR2, change the set value of the following
parameters, if necessary.
• Precharge/Discharge Time (F.014)
• Wattage of Precharge/Discharge Resistor (F.015)
Table 4.5
Maximum Applicable Capacitance of Capacitor and Minimum Resistance Value
Capacitance of built-in Capacitor
Built-in Resistor (Resistance
Value/Wattage)
External Resistor (Minimum Resistance
Value), Connect to PR1 and PR2
External Circuit (Minimum Resistance
Value), Refer to figure 4.5
8720MC-RPS027
990 µ F
4500
µ
F
(33 ohm/80W)
55000 µ F
(30 ohm)
82500 µ F
(10 ohm)
8720MC-RPS065
1900 µ F
7000
µ
F
(22 ohm/120W)
110000 µ F
(20 ohm)
220000 µ F
(4.7 ohm)
External resistor case
Most applications are successfully integrated using the internal
precharge resistor provided in the 8720MC-RPS Regenerative
Power Supply. For instances where there is a large amount of load
capacitance, caused by connecting several 8720MC drives to a
single 8720MC-RPS Regenerative Power Supply, an external
precharge resistor may be required. To determine the total
capacitance C[F] add the capacitance for the applicable RPS027 or
RPS065 unit, as determined from row 1 of Table 4.5, to the sum of
the drive capacitance as determined by the drive specifications in
Chapter 2 of the 8720MC-RPS User Manual, Publication 8720-UM-
001-B-US-P FEB 2001. In the case of the RPS027 if the total
capacitance is above 4,500
µ
f, but less than 55,000
µ
f an external
precharge resistor connected to PR1 and PR2 is required. In the
case of RPS065 if the total capacitance is above 7,000
µ
f but less
than 110,000
µ
f an external resistor connected to PR1 and PR2 is