Cisco C3K-PWR-1150WAC PSU Connection out of RPS2300 rack C3K-PWR-750WAC

[Robert763]

Following a discussion on the TEA thread I got a couple of Cisco redundant power supplies intended to power network swtches with PoE. These consist of a 1U rack unit, the PWR-RPS2300 with two slots that each take a 750W (C3K-PWR-750WAC) or 1150W (C3K-PWR-1150WAC) PSU module. Power input is 115/23V auto ranging by a IEC inlet on the front of each PSU module. The rack provides a cooling fan, supervision and switching of DC power to up to 6 switches with selectable priority in case of failure or excess power demand.
The PSU modules have 2 outputs, 12.25V and 52V. When in the rack they are configured as +12.25V and -52V with 0V common to both outputs and the chassis ground.  Outside the rack the 12v and 52V outputs are isolated from each other and chassis. This means the 52V can be used as positive WRT to common. The 1150W PSU has built in fans, 25A 12V  and 16.4A 52V ratings.

The problem is that these will not power up outside the rack and there is no published information on the interconnect that I can find. But I want a 800W+ >35V power supply for a project without the rack..... I got one of each PSU model and a RPS2300 and set to work finding a minimum configuration that worked. As these have serial communication I was not certain it was possible. The control connections are 16 square pins on a 4x4 0.1" matrix. I decided to make up some 4 way extension leads to run it out of the rack and then see which rows and then which pins were required to power it up.

I narrowed it down to two pins which is good. It was likely to be a passive interface as the rack has no separate power supply and it's hard to do anything active with just two wires. I then investigated the matching connections on the rack. Long story short, to turn the PSU on you just have to connect a 1k resistor between pin 6 and pin 15 
The fans on the 1150W seem to respond to load and are very quiet off-load (on my unused unit at least) but I've not tested at full load yet. The hack will probably work on the C3K-PWR-265WAC PSU too.

Marked up image below.