Hooking two mismatched power supplies together (Grounding / floating voltages)

Hello,

I am trying to build an Arduino project which logs voltage and current drawn by devices under test.

I am trying to avoid is blowing up the Arduino, because the power supplies are grossly mismatched.

Powering the Arduino is a 9V wall wart (your typical Arduino power supply.) Powering the device under test is a 32V @ 30A switcher. The devices under test will be six to ten feet away from the power supply. Even using 10ga wire, my rough researched calculations are showing 1V to 2V drop along the length of that wire @ 30A. Because of this I am worried that a floating ground issue might cause electrons to flow where they shouldn't.

Based on my reading so far to avoid floating ground issues, I have come up with the following so far: Does anyone see any problems with this design, that might cause the device under test to dump current across the Arduino and it's shields?

Notes about the design for the curious: The ACS715 current sensor is a hall effect sensor, there is no electrical connection between the high current side and Arduino. The LM4040 would be used as a precision analog reference. The blue wires running from the Arduino to the power supply are for remote controlling power supply output voltage and current limits.

Thanks in advance for any wisdom you can impart.

It actually looks pretty good. Hopefully you will not use wires as long and "loose" as you have drawn them, as you might be inviting noise issues into what you expect to be a precision measurement, but I don't see any potential for damage given your drawing. Unless...your voltage divider resistors are too low in value and the wrong values :)

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That BK power supply is sure a nice looking unit and I would sure like to have one, but at like $700 list that ain't going to be happening. ;)

Good luck on your project.

Lefty

RuggedCircuits: Hopefully you will not use wires as long and "loose" as you have drawn them

Thanks for the response! And of course not, just trying to draw the rats nest in Visio in a way thats understandable. I'll try to avoid the more mundane ways to blow up the Arduino, as in choosing the wrong resistor values :P (By the way, I saw the 'rugged Arduino' project, very nice! Are there updates coming for the R3 version?)

retrolefty: That BK power supply is sure a nice looking unit and I would sure like to have one, but at like $700 list that ain't going to be happening. ;)

I know, me too... I have one on my coffee table I borrowed from work to play with on this design, and I am so not looking forward to having to bring it back into the office :'(

I'll try to avoid the more mundane ways to blow up the Arduino, as in choosing the wrong resistor values

It's surprising how many people get those resistors backwards. If you're measuring 32V and expecting 5V out of the voltage divider, getting the resistors backwards means you'd get 27V instead, which could be disastrous (except on a Ruggeduino ;) )

Are there updates coming for the R3 version?

Updates for R3? like what? We added a diode from reset to +5V to match the latest Uno, but I don't think there are other differences (we can take this to PM rather than taking this thread on a tangent)

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