3kW Cisco Server Supply teardown and help needed

[Da_Stier]

Hi all,

some time back I bought a Cisco Ws-cac-3000w power supply on ebay.
(I just realised, that this was almoust a year ago, oh well...)
These are available for around 35€.
It is a 3000W supply, made to provide 42V at up to 66A when supplied by 230V.

There is also a 6000W version, which consists of two slightly different 3kW units in one case.
And there is also a 4000W version, which is completely different on the inside.

My idea was / is to modify the 42V rail to be somewhat controllable. (around 5V to around 48V would be ideal)
I want to use it as a kind of high power lab supply, mainly for supplying LDMOS amplifiers and other high power devices.

This is the supply (pictures from ebay):









The next part is a small teardown of my unit to show the interals:

This is the input filter of the unit.


The supply consists of 3 boards.
The first one is the small input filter board shown above.
The second one is this board which is the power factor correction board.
It outputs the rectified supply voltage to the main board.


This is the main board with all the switching converters.






The 42V rail is controlled by an ADM 1041A on a small daughter card.
This is the datasheet for the ADM1041A:
ADM1041A.pdf

This is the daugthercard:


Fortunately all the connections to the mainboard are nicely labeled.



So now for the modifications.
There is another thread on this unit and the bigger 6kW model of these supplies on the german mosfetkiller forum.
https://forum.mosfetkiller.de/viewtopic.php?f=2&t=63559&sid=c356e318a5768a60b20874e5bcde014d&start=105
(Unfortunately completely in german)
The picture of the unit on page 8 of this thread is about what I would like to do.

To start I looked at the typical application circuit of the ADM1041A.

Am I right in the assumption, that the easiest thing to try would be to simply change the voltage at the Vs+ pin of the IC?
Like this I should be able to modify the output somewhat I guess.
Of course at some point the over- / undervoltage protection will kick in.
According to the datasheet, the Vs+ line expects a level between 0 and VDD+0.2V.
With VDD being 5.5V max.
So I guess by adding a potentiometer into the feedback line I should be able to change the output both up and down,
depending on how much feedback I give?

There also is a thread about using the I2C interface of the IC to change the voltage, however this only works from around 41V to around 49V.
This isn't quite enough for what I want.

Would it also be possible to change the 2V5 reference of the IC?
I guess this should directly reflect in the output, right?
Or will this mess up everything else as well?
... Like generally speaking of course, not in this exact circumstance.

I'm somewhat unfamiliar with DC supply design at these powerlevels, so I thought, some of you might have some ideas / recommendations or maybe even experience with these supplies.
I have done some more reverse engineering of the circuit, however I can't find my notes right now - which is somewhat emberassing - , so I thought, I start the thread with a small teardown instead. 



Thanks and greetings,
Michael