Electronics > Projects, Designs, and Technical Stuff
Tie DC PSU 0V to mains earth?
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GoneTomorrow:
Long story short I'm designing a controller for some industrial equipment. There's a couple of opto-coupled inputs designed to take a non-polarised 24VDC signal, basically just an on-off input, into the micro. When it comes to the particular installation one of the inputs will be connected to a remote timer with a relay output. To get it to work I'll take 24V from the PSU on my controller board and send it up a wire, through that remote relay, and then back into one side of the optocoupler, and then ground the other (to 0V on the PSU).
The PSU I'm using is a small PCB-mount Meanwell with an isolated DC output, which means that presumably the output will be shifted about halfway up the mains voltage relative to earth due to the filter capacitors. Should I tie the 0V/GND output of this PSU to mains earth so that it's not floating at 100 ish volts? Does it matter in this case? What are the considerations when deciding whether to use a floating DC output or tie it to ground? I assume one would be ground loops or stray currents flowing between things, which doesn't apply in this case.
Cheers!
Gyro:
If your inputs and outputs are optos and relay type devices then I would probably opt for grounding the supply output. You're unlikely to meet any ground loop issues in these circumstances - in fact Y cap leakage currents on the outputs could be more troublesome (and also for your internal micro's I/O pins if you're using a scope or other grounded test gear during debug). ESD susceptibility and ease of clamping might be another factor.
I work on the basis of 'is there a compelling reason for not having an internal supply ground referenced?'.
GoneTomorrow:
Didn't even realise this had posted as I got a HTTP 500 when I submitted it.
Thanks, I guess that makes sense to look at it that way: "is there a reason to not ground" vs "is there a reason to ground."
I think I've just been mentally scarred about proper grounding (or not) after dealing with professional audio equipment. Changed my mounting holes to pads connected to the ground plane.
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