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A Question About Non-isolated AC Ground To DC Negative.

A.Justice

Swears he didn't start that fire.
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Just want everyone needs, another potential grounding issue! Here goes;

I modified a Dell Z750p 63 amp, 120v to 12 volt server power supply to feed a 40 amp Renogy DC-DC converter, for a "shore power" connection of sorts.

Mains power --- Dell PSU --- DC to DC converter --- battery --- inverter.

My trailer mounted system is floating (if I understand the term correctly), inverted AC is isolated, I don't run any loads through the frame, and all DC loads have dedicated negative wiring.

However, there is continuity between the AC mains ground, and the DC rail of the PSU (as well as the case). Which means that while the DC to DC charger is plugged in to the PSU, the entire system has a "real" ground, through the negative DC wiring.

From what I understand, that is okay when all is well. BUT, if a ground fault were to occur, on either the PSU, inverter, or on the mains side, what would happen? I wouldn't want any AC current going up (or down) the negative rail. I also wouldn't want the normally safe, low voltage, DC wiring becoming live and shocking someone, or frying everything attached to it.

Should I figure out how to isolate the DC side of the power supply from the AC ground? I'm pretty sure the continuity comes from the PCB being mounted to the metal case, and isn't "hardwired", so I could probably add insulation to isolate the AC and DC sides if necessary.

Any help or advice is appreciated!
 
What is the resistance reading between AC plug ground prong and the Negative DC output of the Dell?
 
However, there is continuity between the AC mains ground, and the DC rail of the PSU (as well as the case). Which means that while the DC to DC charger is plugged in to the PSU, the entire system has a "real" ground, through the negative DC wiring.
I don't think you said it explicitly, Is the dc2dc converter isolated or does it a have a common negative?
 
I don't think you said it explicitly, Is the dc2dc converter isolated or does it a have a common negative?
I'm not exactly sure what you mean by that. Because of the continuity, all the negatives in my system are technically connected and share the same 0 volt reference, if that's what you are asking. Edited, it doesn't, I made a mistake.
 
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I'm not exactly sure what you mean by that. Because of the continuity, all the negatives in my system are technically connected and share the same 0 volt reference, if that's what you are asking.
There are 2 flavours of dc2dc converter.

Isolated like this.
Typically these have 2 negative terminals.

and non-isolated like this.
Typically these have 1 negative terminal also called common negative.
 
There are 2 flavours of dc2dc converter.

Isolated like this.
Typically these have 2 negative terminals.

and non-isolated like this.
Typically these have 1 negative terminal also called common negative.
I have the isolated Renogy 40 amp unit.

I just tested the continuity through the DC converter, and it isolates the PSU from the rest of my system. I must have missed that somehow. I think you solved my "problem". Much appreciated!
 
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