Referencing grounds and a RC power supply

I have recently converted a Server power supply to use as a “bench” supply to charge my RC Multicopter batteries. Here is the tutorial that I’ve followed to make the my current 12v version http://www.daddyhobby.com/forum/showthread.php?t=77204. I’ve been working on a circuit board (labeled “supply interface” below) to replace the one that is removed in the tutorial. I’m hoping that the supply interface would enable me to use a Arduino Mega with a TFT shield to operate a few of the controls and monitor temperature. The mega would communicate with a arduino mini located on the supply interface.

My goal is to control two supplies running in series as outlined in the tutorial for a 24v supply. Once I started to think about how the two supplies and all of the control stuff would be connected I really started to wonder about grounds. Here is a block diagram that got me thinking:

On the left is the mega, in the middle is the supply interface, and on the right is the power supply. Starting simple, if I maintain two grounds on the interface for the second power supply like this:

Would that keep the two grounds isolated without causing any problems while maintaining the ability to run the supplies in series?

Then as a follow on question is it possible to add a digital pot (controlled by the mini) between +5 from the power supply and the VOLT_ADJ pin, as well as read the speed of the power supply’s fan without complicating things too much?

Thanks a ton,

Loren

Your post seems to be missing the images, or I'm having and issue and can't see them...

I really started to wonder about grounds...

If the "ground" is not really grounded, you can connect power supplies in series. You need to check the specs or test it with an Ohmmeter (multimeter). There should be no connection (infinite resistance) between the power supply's common/black/negative connector and the chassis, or between it and the common/black/common on the other power supply.

If the common/black/negative output IS truly grounded, you CANNOT connect two power supplies in series.

It is unusual to connect two power supplies in series. Normally if you need a 24 Volt supply, that's what you buy/build, unless it's an "emergency".

However, it's not so uncommon to ground the negative output on one supply to get a positive voltage, and ground the positive output on the other supply to get a negative voltage.

DVDdoug:
Your post seems to be missing the images, or I'm having and issue and can't see them...

I've attached the images to the post. Hopefully that will help to illustrate my questions

DVDdoug:
If the "ground" is not really grounded, you can connect power supplies in series. You need to check the specs or test it with an Ohmmeter (multimeter). There should be no connection (infinite resistance) between the power supply's common/black/negative connector and the chassis, or between it and the common/black/common on the other power supply.

That's the idea here. The tutorials that I've read will completely isolate the ground on the output (DC) side from the AC side.