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Two N5751A supplies with paralleled outputs - no secondary current

Question asked by dave.natrop on Dec 11, 2014

I have a configuration of two N5751A supplies with outputs wired in parallel.  The secondary unit is not outputting any current.

The output voltage is set for 150 VDC, the OVP is at the power-on default (300 VDC), the UVL is at the power-on default (0 VDC),  and OCP is disabled.  The primary delivers power, but there is no current output from the secondary unit.  Per the instructions on pages 30 to 32 of the N5700 Users’ Guide, I have the outputs wired with 12 AWG  wire in parallel approximately 12 inches from the supply outputs.   Remote sensing has a sense point (+S, -S) connected to the primary and then a parallel connection from the primary to the secondary remote sense inputs.  Using the rear panel J1 connector, there is a conductor from primary J1-25 to secondary J1-10.  There is a jumper wire from J1-8 to secondary J1-12.
On the primary, SW1-5 is UP and all other positions are in the factory-default DOWN.  On the secondary, SW1-2 and SW1-5 are UP.  All other position on the secondary SW1 are in the factor-default DOWN.

Using the Limit button, I set the current limit on the primary to 1.0 A.  Likewise, on the secondary I set the current limit to 1.2 A  When I enable the outputs of both the primary and secondary, I can increase the output voltage by turning the voltage adjustment **** on the primary.  The display on the secondary indicates that its voltage is the same as the primary.  On the secondary, neither the voltage adjust **** nor the current limit **** have any effect since the secondary SW1-2 is in the UP position.  The voltage of the secondary unit cannot be set independent of the primary (higher or lower) because the voltage adjust **** has no effect.

With a load of 0.50 A connected to the paralleled outputs of the supplies, the primary display indicates it is delivering current.  The secondary display indicates a voltage, but the current value remains at exactly 0.  The constant voltage (CV) indicators on both supplies are on.  The constant current (CC) indicators on both the primary and secondary are off (not illuminated).  The PROT indicators on both supplies are off.  Changing the load demand either up or down has no apparent impact on the secondary.  It delivers no current.  

In trying to debug, I temporarily decoupled them.  I verified that each supply, when configured as independent (stand-alone) power supplies, is capable of delivering their full rated current into my load.

Where am I going wrong?


Edited by: DNatrop on Dec 12, 2014 4:06 PM (typo)