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Topic: Grounding 5V DC to Earth Ground? (Read 864 times) previous topic - next topic

pekasus

I have this 120VAC to 5VDC transformer on my pcb http://www.cui.com/product/resource/vsk-s10-series.pdf

I use the +5V side to power my project. Do I have to keep the -5V side separate from earth ground? Also, in the schematic in the datasheet, there is a part that should be tied into chassis ground. Can this just go to earth ground?

Thanks in advance!

LarryD

#1
Jul 03, 2013, 04:46 am Last Edit: Jul 03, 2013, 04:52 am by LarryD Reason: 1
See attached diagram
The way you have it in your schematic isn't the same as how you have it wired up!

pekasus

Thanks so much for that!

So it looks like I keep the 0V after the transformer separate from earth ground.

The only issue that I have is that I am planning on using 3-wire 14AWG to carry 240V in the US, so it is hot-hot-ground with no neutral. Is there any problem that I am not aware of in tying chassis ground into the same earth ground as the transformer. The earth ground and neutral busses are connected in most panels I've seen anyway.

Thanks!

LarryD

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• universal input (85~264 Vac / 120~370 Vdc)


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I have this 120VAC to 5VDC transformer

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I am planning on using 3-wire 14AWG to carry 240V


So you are going to use 240VAC to power the AC-DC POWER SUPPLY?

The way you have it in your schematic isn't the same as how you have it wired up!

pekasus

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So you are going to use 240VAC to power the AC-DC POWER SUPPLY?


No. I am going to use one hot leg (120V) and was planning to use the earth ground as opposed to bringing in a neutral as well since the earth ground and neutral are usually connected at the panel anyway.

MarkT

That power supply has 100uA leakage current, so you'd be best to ground the 0V output otherwise it'll
float at some sizable fraction of mains ac voltage.
[ I won't respond to messages, use the forum please ]

tocpcs


I have this 120VAC to 5VDC transformer on my pcb http://www.cui.com/product/resource/vsk-s10-series.pdf

I use the +5V side to power my project. Do I have to keep the -5V side separate from earth ground? Also, in the schematic in the datasheet, there is a part that should be tied into chassis ground. Can this just go to earth ground?

Thanks in advance!


Is not -5VDC but rather 0VDC or GND.
Tying that ground to earth is fine in my opinion.
I'd be thinking of how I was isolating that second hot wire actually, it's still an exposed core within the cable.

pekasus

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That power supply has 100uA leakage current, so you'd be best to ground the 0V output otherwise it'll
float at some sizable fraction of mains ac voltage.


Thanks for that. I hadn't considered that. The only question is do I have to worry about bypassing the RF filter?

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Is not -5VDC but rather 0VDC or GND.
Tying that ground to earth is fine in my opinion.


The labels on datasheets are confusing sometimes. I thought it should be 0V originally, but they labelled it +Vo and -Vo, so I thought Vo was a constant 5V. Thanks for the clarification.

Quote
I'd be thinking of how I was isolating that second hot wire actually, it's still an exposed core within the cable.


The second hot wire just does a u-turn on the board and goes to a set of output terminals. I have well over the 0.4mm isolation required between routes.

Thanks for all your help!

LarryD

#8
Jul 03, 2013, 08:29 pm Last Edit: Jul 04, 2013, 12:03 am by LarryD Reason: 1
Quote
I am going to use one hot leg (120V) and was planning to use the earth ground as opposed to bringing in a neutral as well since the earth ground and neutral are usually connected at the panel anyway.

Yes the Ground and Neutral are connected in the breaker panel but:
Using the Ground as the Neutral return is illegal.

Why don't you want to use both Hots?

EDIT:
I would definitely recommend a fuse for both L1 and L2
The way you have it in your schematic isn't the same as how you have it wired up!

pekasus

That's a good point. I can do that. I just have to make a minor adjustment to the routing.

Thanks!

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