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DOC-MN-008-03, VCCS300 User Manual
Connecting units in parallel
VCCS300 units of the same type can be paralleled in any number to achieve higher output currents. To parallel the outputs simply connect all the positive power
cables together and all the negative power cables together. No other external circuitry is necessary.
For best performance and increased reliability, it is recommended to enable share mode on each unit (See “Share Mode (Droop)” section below for details).
The accuracy of current sharing is highly dependent on external cable resistance. To minimise errors, it is important to have equal cable lengths from each output
terminal to the common connection point for both positive and negative cables.
Below is an illustration of optimised parallel connection of three units to give 900W of output power.
Share Mode (Droop
)
When paralleling multiple units, share mode should be enabled by sliding SW1 to the share position as shown below.
This will introduce a +/-2.5% slope to the load regulation that enables the paralleled units to share load current equally between them and increase system reliability.
In share mode, the output voltage of each unit has an artificial voltage drop added that reduces the output voltage as the current increases. At 0% load the voltage is
typically V
NOM
+2.5%, at 50% load it is V
NOM
and at 100% load it is V
NOM
-2.5%.
Normal Mode
For normal parallel mode, SW1 should be set to normal position. In this mode, the highest set output will supply all the load current until its current limit is reached. If
the load demand exceeds this level the output voltage will drop to the level of the next highest set output and that output will begin to supply the load current while
the first output continues delivering full current. This process repeats for the total number of paralleled outputs. Typically, system reliability is reduced in this mode of
operation as the higher set outputs will do most of the work with the lower set outputs only delivering current during peak load demand.
Ripple
When outputs are paralleled, the output ripple may contain frequencies in the audio spectrum.
WARNING!
•
Energy and voltage hazards may arise when individual units are paralleled. When safe energy and voltage levels are exceeded ensure that an
appropriate warning label is affixed to the power supply in a manner that service personnel will always notice it. See the Safety section for more
details.
•
Leakage currents will increase when multiple units are installed in an end-system.
