Question About Ground Wire on AC-DC Power Supply from Mean Well Inc

[Potomac]

Hi all,

Super beginner question to do with an AC power supply

I bought this little power supply from Mean Well (reputable maker) that fits nicely on to a perf board that I'm mounting on aluminum hex standoffs.  It's the one in the first two pictures below.   Here's the power supply data sheet:  http://www.mouser.com/ds/2/260/IRM-15-SPEC-806085.pdf

I disconnected a spliced mains wire that I had connected to a bigger power supply.  It has a black "live / l" AC wire, a white "neutral / n" AC wire, and a green "ground" wire.

My two questions are:

1). Where should I connect the green "ground" wire?  There is no ground pin on this particular IRM-15 power supply.  I believe on the bigger one, the grated metal case serves as the ground. 

2). Could I connect the green ground wire to a piece of metal that I would then use as "common" ground for my project?

3). I was planning on soldering the pins/wire connections to the perf board, and covering the connections with heat shrink plastic melted with a heat gun. Will this work?

[IanB]

I disconnected a spliced mains wire that I had connected to a bigger power supply.  It has a white "live / l" AC wire, a black "neutral / n" AC wire, and a green "ground" wire.

One tiny detail: black is hot, white is neutral.

[Potomac]

^ Whoops. Thanks for pointing that out Ian. just made the correction in my post

Is my plan for the making the ground right or wrong?  I have a scrap piece of aluminum I was going to connect it to

[IanB]

^ Whoops. Thanks for pointing that out Ian. just made the correction in my post

Things don't look good on the terminals of the other power supply you pictured.

Is my plan for the making the ground right or wrong?  I have a scrap piece of aluminum I was going to connect it to

If you are going to put your project in a metal case you can bolt the ground wire to the case using a crimp lug.

If you are putting your project in a plastic case or are just experimenting on the bench, you can tape up the end of the ground wire and ignore it.

However, when you have a mains powered project you should really put it in a case of some kind and make sure the mains supply has a fuse and stress relief for the cable.

[Zero999]

Yes, Ian is correct, the ground wire needs to go to the metal enclosure, if it has one, otherwise it doesn't have to be connected.

One thing which would worry me is if there's enough clearance between the mains and the output of the power supply on the perf board.

[IanB]

Also, with an encapsulated power supply like that, you should not solder the mains input pins into the perfboard. That will undermine all the mains isolation present in the power supply. You should instead mount the power supply with the DC end at the edge of the perfboard and the AC end overhanging and far away. Then create a separate sub-board for the mains input. After that make sure the whole assembly is mechanically well supported and secured so it can't wobble or vibrate.

(See what Hero999 just posted above me.)

[Potomac]

Do you guys mean like this this? (Birdseye view how I'd do the wiring)

[Kjelt]

Also on the mains side use a decent connector , strain relief on the mains wire, and under the mains pcb a plastick sheet for extra isolation if you are going to mount it in a metal case or just so no-one will kill himself accidently when handling the board while it is still mains powered. Yeah everyone knows he shouldnt tiuch it but accidents happen and it is your job as an EE engineer to make sure that even a child without knowledge will not be able to touch the mains under any condition. Oh yeah and use a fuse in front of the psu.

[IanB]

Do you guys mean like this this? (Birdseye view how I'd do the wiring)

Yes, that would be the concept. It provides a large air gap between the mains side and the low voltage side.

[Potomac]

Would this power supply in this style have been an easier thing to integrate onto the perf board directly?  It has green "Phoenix" connectors that just screw in the wires

Would I still have to use 2 boards? Would the AC mains be isolated properly?

I would just epoxy glue this to the perf board for the convenient form factor I want (hex standoffs that match my other project perf boards)



http://www.mouser.com/ds/2/260/IRM-60-spec-806142.pdf

[Potomac]

The usefulness of a metal case keeps coming up.

Maybe I should just stick with this switching 5V-12V supply instead that I briefly mentioned in my first post.

I think I got a crappy recommendation from someone I know to go with that encapsulated plastic one that lacks a metal case (IRM-5)

http://www.meanwell.com/webapp/product/search.aspx?prod=rd-65

[IanB]

Would this power supply in this style have been an easier thing to integrate onto the perf board directly?  It has green "Phoenix" connectors that just screw in the wires

But why do you want to put it on the perf board? You would fix that power supply separately to the case using its mounting holes and then take trailing leads from the DC terminals to the perf board. That would give you the whole area of the perf board for circuit components.

That other supply with through hole solder pins is designed for people who can make a custom board layout with proper clearances and isolation distances. If you just try to stick it in a perf board you are mixing mains with low voltage circuits on the same board. That is not safe. Where possible mains voltages should be kept off board and far away.

[Potomac]

^ Ian, to answer your question, here is a VERY INCOMPLETE view of how the rest of my project is laid out on a piece of plexiglass.  I'm testing 12 (soon to be 16) IR transmissive slot sensors to see how consistent the data is across a batch of them.  The yellow wires are going into the analog inputs of my Arduino.  Everything is on hex standoffs and perf boards for ease of removal.

The perf board just fits in conveniently with everything.  But I can see your point about the mains being far away.

Maybe I will just use the silver grated powersupply box.  (Circled in orange.  The other orange circle is the encapsulated power supply. And below that in blue is a Constant Current device for the LED's in the sensors that I was considering using)

[T3sl4co1l]

The ONLY thing that ground serves, is to sink protective fault currents from the line.

If you have a metal enclosure, you must either:
1. Ground it, so if the enclosure becomes energized from a loose wire inside, it shorts out and blows the fuse, or
2. Insulate it, so if it becomes energized, hazardous voltage is still not exposed to a user. (This is called a "double insulated" appliance, and may not be legal everywhere.)

Note that your Arduino is grounded, or can be (via USB to an also probably grounded PC).  It would probably be a good idea to maintain that, so that if a line wire goes somewhere it's not supposed to, you don't get shocked (or cause damage) plugging in a USB connector, or touching the low voltage parts of your circuit.

Speaking of, there is also terminology for the low voltage side.  If there are two insulation layers between mains and LV, you have reinforced insulation, and it is SELV, safe extremely low voltage (no mains connection, insulated to >= 2.5kV RMS, not susceptible to a single-point failure).  It can remain isolated, or you can ground it as needed.

If you didn't have reinforced insulation, but a single layer ("basic"), you would have to ground your SELV circuit, because otherwise a single failure (of that single "basic" insulation layer) could connect it to mains.  Grounding it provides a path for fault current, blowing the fuse and returning it to a safe condition.

Speaking of, you need to be sure there is fusing on the hot mains lead (sometimes, the neutral requires a fuse as well, in case of possibly reversed wiring).  Usually, those power supplies have this inside... but you can't very well verify that, can you?  It's in a solid black box...   So, best practice also to add a fuse.

Finally, keep all the mains connections well insulated, tied down, away from fingers.  Preferably closed under a cover that requires a tool, such as a screwdriver, to open.  (And guess what, if the cover is insulating, it counts as another layer; if no live wires are physically touching it, then there's another layer of insulation as well, be it air or wire insulation or what; and the two combined therefore counts as reinforced insulation, so you're golden!  Or if it's metal, simply ground it, and you're still golden.)

Follow all these rules, and you will have a good chance of getting UL approval, which means if anyone else touches the thing and gets zapped, you aren't liable for damages.  A big deal, if you later discover you can make and sell a million of something!

Even if it's just a one-off, these rules should at least make you familiar with what's needed to build and handle a project, safely.  No, I certainly wouldn't expect you to get UL approval for a stack of proto boards -- testing is in the $10k range! -- but if you ever develop something for market, this also gives you a good idea of what's needed and worthwhile.

Tim

[jeroen79]

Do you guys mean like this this? (Birdseye view how I'd do the wiring)

Yes, that would be the concept. It provides a large air gap between the mains side and the low voltage side.

Wouldn't it be enough to just get rid of the unused soldering islands around the mains AC pins?

[Potomac]

I have two of the IRM-15 power supplies, and at $5 each, they are somewhat expendable.

I did a test perf board in the picture below.  I covered the solder joints below in epoxy. Is this safe?  Someone advised me this could be a quick and dirty solution that's safe.  The epoxy acts as an insulator like heat shrink? 

I added some standard pins to the board.  Then I found a poached a UL-rated cable from a really crappy $10 RadioShack soldering iron.  It doesn't have a ground wire, so that's convenient and doesn't leave me with a third line hanging.  I solder spliced it and then heatshrunk it

I tested the output pins, and I'm getting 5 volts with a multimeter. So far so good?

[Potomac]

Just replying again for feedback on the glue job above. Safe or unsafe?

[IanB]

That's not something I would want to plug into the mains.

[Ysjoelfir]

I personally would plug it in, but I don't advice to do it as it isn't the right and safe way to do it.
But we have to be honest - I would bet that most of the things we all build in our labs and tinker around with aren't safe or recommended to do the way they were done.
Sure, you COULD still get a shock from this, if you try to. But guys, please, in most cases this should be okay.
We have to remember that it isn't a permanent fixture but just for experimental uses. If you would like to go the extra mile you could / should drill away the unused pads between primary and secondary side of your perfboard or even better, use a dremel tool to create a slot underneath the AC/DC converter.
We have to keep in mind that those miniature converters are designed to be sondered on a permanend PCB, so what should be wrong with hhis attempt, except for one thing:
I personally don't like the connectors you used as those are definitely not suitable for mains voltage, but even that should do no harm if you are careful, even though I would have sondered the mains lead on permanently.

[rch]

Just replying again for feedback on the glue job above. Safe or unsafe?

It would only be safe if it was in either an earthed metal enclosure, or a closed plastic enclosure with x (local rules) separation from the live parts, and had mains fuse and strain relief for both mains and outgoing extra low voltage wires.etc.  Then you either have this enclosure physically separate from your plexiglass setup joined only by the floating extra low voltage wires (assuming your power supply adequately isolates the mains, need to check the data sheet)   or you have to have the whole plexiglass in such an enclosure and make special arrangements to check the insulation of any signal outputs and inputs.   That would probably be a big nuisance and hard - so you see why nearly every low power consumer item has a wall wart!   Experience suggests that if your project has no mains going into it except to a separate well insulated mains powered extra low voltage unit things will be safer and more convenient.

[Potomac]

Thanks for the feedback all.

I think I'll scrap the idea of using this Meanwell encapsulated power supply for 2 reasons:

1). Safety concerns mentioned
2). It doesn't supply a constant voltage, which I think may enhance the operation of these IR emitter-detector package sensors.  There are some subtle voltage spikes with that Meanwell Supply that are giving me faulty readings compared to the regulated Variable benchtop supply I was using previously

Instead, I'll migrate to a 12 volt "wall wart" connected to this 5V constant current board from Sparkfun.  I'll mount that thing on another perf board.  Should be a safer looking with a smaller footprint

Does this sound like a better plan?

https://www.sparkfun.com/products/13032

•6-12V input voltage via barrel jack or 2-pin header
•3.3V or 5V regulated output voltage
•800mA Operating Current
•PTC fuse protected power

[Potomac]

Bump. Any feedback on the new power supply device? (Sparkfun)

[FlyingHacker]

Spark fun tends to make decent stuff, possibly a bit overpriced at times.

Wall warts are typically one of the safest solutions as the mains is all handled in the wart. Note that cheap wall warts are often really crappy in terms of safety. Check YouTube for tear downs. So get a decent one, and make sure it can handle the current needed to feed your load.

[tggzzz]

I'm testing 12 (soon to be 16) IR transmissive slot sensors to see how consistent the data is across a batch of them.  The yellow wires are going into the analog inputs of my Arduino.  Everything is on hex standoffs and perf boards for ease of removal.

Depending on exactly what you are measuring and exactly how (details matter), you may find the long wires (both signal and ground) cause errors due to EMI and due to inductance.

You will need to check that the Arduino's analogue input has sufficient resolution, accuracy and has sufficiently low noise.