Rockwell Automation 1606-XLS960EE Power Supply Reference Manual - Manual (Page 24)

All parameters are specified at 24V, 40A, 230Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
24 Rockwell Automation Publication 1606-RM029A-EN-P — April 2014
Bulletin 1606 Switched Mode Power Supplies
25.6. Parallel Use to Increase Output Power
Unit A
AC
DC
Unit B
AC
DC
-
+
-
+
Load
+
-
Power supplies from the same series (XLS) can be paralleled to increase
the output power. The output voltage shall be adjusted to the same value
(±100mV) in “Single use” mode with the same load conditions on all units, or
the units can be left with the factory settings. After the adjustments, the
jumper on the front of the unit shall be moved from “Single use” to “Parallel
use”, in order to achieve load sharing. The “Parallel use” mode regulates the
output voltage in such a manner that the voltage at no load is approx. 4%
higher than at nominal load. See also section 6. If no jumper is plugged in, the
unit is in “Single use” mode. Factory setting is also “Single use” mode.
If more than three units are connected in parallel, a fuse or circuit breaker with a rating of 50A or 63A is required on
each output. Alternatively, a diode or redundancy module can also be utilized.
Energize all units at the same time to avoid the overload Hiccup PLUS mode. It also might be necessary to cycle the input
power (turn-off for at least five seconds), if the output was in Hiccup PLUS mode due to overload or short circuits and the
required output current is higher than the current of one unit.
Keep an installation clearance of 15mm (left / right) between two power supplies and avoid installing the power
supplies on top of each other. Do not use power supplies in parallel in mounting orientations other than the standard
mounting orientation (terminals on the bottom of the unit) or in any other condition where a derating of the output
current is required (e.g. altitude, above 60°C, …).
Pay attention that leakage current, EMI, inrush current, harmonics will increase when using multiple power supplies.
25.7. Parallel Use for Redundancy
Power supplies can be paralleled for redundancy to gain higher system availability. Redundant systems require a
certain amount of extra power to support the load in case one power supply unit fails. The simplest way is to put two
power supplies in parallel. This is called a 1+1 redundancy. In case one power supply unit fails, the other one is
automatically able to support the load current without any interruption. Redundant systems for a higher power
demand are usually built in a N+1 method. E.g. five power supplies, each rated for 40A are paralleled to build a 160A
redundant system. For N+1 redundancy the same restrictions apply as for increasing the output power, see also
section 25.6.
Please note: This simple way to build a redundant system does not cover failures such as an internal short circuit in
the secondary side of the power supply. In such a case, the defective unit becomes a load for the other power supplies
and the output voltage can not be maintained any more. This can be avoided by utilizing redundancy modules, which
have decoupling devices (diodes or mosfets) included. Further information and wiring configurations can be found in
sections 24.3 and 24.4.
Recommendations for building redundant power systems:
a) Use separate input fuses for each power supply. A separate source for each supply when possible increases the
reliability of the redundant system.
b) Set the power supply into “Parallel Use” mode.
c) Monitor the individual power supply units. Therefore, use the DC-OK relay contact of the XLS power supply.
d) It is desirable to set the output voltages of all units to the same value (± 100mV) or leave it at the factory setting.