No ground on power supply - does it matter?

Just opened a new power supply. It has a 3 pronged plug for the wall, but only 2 connectors in front for + and - voltage, but none for ground. I used to have a mean well power supply that had the +, -, and ground inlets. I used to have my arduino ground plugged on that power supply ground, but with the new one that seems impossible. Is that a problem?

I'm controlling 14 solenoids and the power supply is for them. 13.8v at 10 amps. I guess I have no way to connect ground now? Wondering if I need to return his power supply and look for another one, then is it's exactly the voltage and amp requirements I need.

Hmmm, just realized my Mean Well supply had a +, -, and ground to attach a plug to it for the wall, but only +, and - to plug things to the power supply. Now, my new one is similar, but enclosed completely, so there is no way I can reach that ground plug.

How do you ground the arduino is such a case? I was planning on using this power supply for the Arduino nano. No computer used, so the PSU is the only thing plugged in the wall.

Is the circuit all dc and powered by the power supply? The ac mains ground is literally a connection to earth. The power supply itself should be grounded to earth for a number of reasons.

The “ground” for the solenoids and the arduino do not need to be earthed. They can to be tied to a point considered to be zero. This is the negative terminal on the power supply, or a battery.

If your project can be powered by an equivalent voltage battery. Then as long as the + is 13.8 volts more than the - , you should be ok. (its a tad high for the nano)

If for some reason you are also switching mains power, or have other mains “earthed” parts of your circuit there may be other factors to consider.

The only thing powering everything is the power supply. So, yeah, the solenoids and the arduino will have a connection to the - of the power supply. I guess I misunderstood and thought they had to be connected to the ground proper. Makes sense now.

The arduino nano says it takes input voltages up to 20v. So, I think the power supply I have is good for it too right?

Ground is an unfortunate choice of word, since it does often lead to an expectation of connection to the actual ground as in the planet and as in the mains earth.

Just as the word "earth" as in the automotive "negative earth" has nothing to do with the planet. (Unless you have metal tyres maybe....)

It's really just the "other side" of the circuit.

I was just confused cause there's 3 wires going into the wall socket, but only two wires going into the power supply. Seemed weird in my head, especially that there is a ground pin on arduino. Kind of made sense to me that the arduino's ground would be connected to a ground on the power supply which in turn would be the ground wire going in the wall socket.

As Jimbo says “ground” is an extremely bad choice of name for what should perhaps be better described as “Low Voltage Circuit Reference”

Generally when talking voltages in a circuit we mean voltages above or below the circuit zero line (the “circuit reference”)

Very rarely would you want to connect the circuit reference to the mains ground.

If your mains connected power supply has a metal enclosure then the casing will be (or should be) “grounded” via the “earth” terminal to minimise the risk of electric shock should a fault occur within the PSU. Double insulated mains units do not require this ground by virtue of superior and multiple layers of insulation in which case they are generally (but not always) connected to the mains via a 2-pin supply lead.

On your metal enclosed power supply, neither the +ve or -ve output terminals should be connected to the metal enclosure.

So, “ground” on your Arduino circuits simply means “circuit reference”

Where I worked when I worked for a living designing industrial control systems we always called it "Com" for common. There were several coms, Acom for analog, Dcom for digital, Pcom for peripherals, all tied to-gether and to power system ground at one point. In addition each com bus was tied to cubicle ground through a capacitor. This may sound like complicated overkill but by keeping tight control of grounding we reduced noise interference and crosstalk between sections very significantly.

On the small systems we are talking about here I would prefer to have the Arduino tied to earth ground by some well defined route.

Don't forget that if you full wave rectify the domestic supply without transformer isolation neither the + nor - can then be tied to "ground" and so you cannot connect signals from this circuit through resistive voltage dividers to the Arduino inputs. I had this problem on the current project and finally broke down and bought a 1:1 isolation transformer to get around it.

In a nutshell, I would suggest the following precautionary steps... (If it sounds simplistic, it's meant to be.. I try to describe things "Screw-Up Proof" :confused: ) (or, simple enough, a 5 yr old can do it.. 5 yr old sold separately. ;D )

1, have a volt meter set to the voltage of the supply

2, connect the Black/Minus probe to the physical case of the supply.

3, touching the Positive/Red probe, to the "-" terminal of the supply.. Worse case, it would read negative voltage. (In the immortal words of the late Douglas Adams, Don't Panic!) IF you get any reading, it means the supply is dual-voltage .. BUT.... if you get a zero reading (No voltage present), proceed to #4..

4, apply the Positive/Red probe to the "+" terminal. You should see a voltage reading. If not, again, don't panic.

5, with the Positive probe still connected to the "+" terminal, connect the Black/Negative probe to the "-" terminal.. it should read the rated voltage of the supply. If More, (i.e. 2X the rated voltage) refer to step #3, where you found it was a dual voltage. If the rated voltage in step #4 read zero, proceed to #6..

6, Okay, at this point, it read rated voltage from + to -, and possibly rated voltage from + to case. if it read zero from + to case, and no other reading other than zero from - to case, it's safe to assume this is a non-grounded standard power supply.. Now... When running projects with the supply, I would highly suggest running a wire from the case, to the - terminal, before running it to the common GND connection of your projects. most single-voltage supplies, the - should already be connected to common GND (yes, this even includes earth GND)

NOW.... IF you got a voltage reading in step #4, you should connect ONLY the case to the GND (and all other devices needing GND) .. and ONLY the "+" terminal to the main supply connection (I.E. Arduino's barrel socket center pin, any device needing the higher VIn voltage.)..

Hope this helps?

Ground is not the same thing as PE (protective earth, the full name for mains earth wire).

For instance during a fault condition PE can jump to high voltages for a few milliseconds before the mains fuse or contact breaker fails. PE is there to provide a low resistance path for fault current and ensure a fuse blows should live wire accidentally touch an earthed metal part, thus limiting the duration of a dangerous voltage. It can't prevent you getting a shock, it can prevent you getting a fatal shock.

Most electronic devices these days are fully isolated and don't need PE connecting at all since there is no way for a live wire to touch a metal case (usually there is no metal case).

Hence the power supply doesn't have PE.

If your arduino is talking to some sort of solenoid control board, you must run a ground wire between the Arduino and the control board, that's a given.

If your arduino ground happens to be connected to PE via its supply its actually a good thing your new supply is isolated - you don't want mains fault currents flowing through your circuit's ground wires, mains fault currents are large.