Does an unconnected power supply move V & A over to its ground connection? - Page 1
Forum section: electronics / beginners

author: Decoman
author_rank: Regular Contributor
timestamp: December 18, 2017, 11:32:07 am
content: I am just wondering, unless I misunderstood things, I believe I have seen people using their variable power supply in youtube videos and set the volt and amps to some value before pressing the output button (playing around with the unit), which would normally push out power to ones electronic circuit, however when not having a thing or some electronic circuit connected to your power supply, does the power supply simply keep the voltage at ready to be pushed, or are there actually electricity flowing anywhere inside the power supply and would any current with any voltage get pushed to an established ground connection back into your wall socket?

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: December 18, 2017, 11:37:55 am
content: Probably the set the max and min current outInviato dal mio SM-G920F utilizzando Tapatalk

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 18, 2017, 12:57:51 pm
content: There are many different designs for bench power supplies. Certainly there are some which switch power very early in the power path while some may simply have a switch at the output terminal. There is no single answer to your question in the Real World. Indeed many bench supplies don't have a switch at all, while some demonstrate rather bad behavior when switched. There is more than one power supply review video on EEV as well as elsewhere that showed poor switch performance.The kind of bench supplies most commonly seen have some amount of baseline power being drawn from the mains/source and certainly with the proper measurement techniques you can "see" the source power being drawn change with the amount of power the supply is "programmed" for, and the amount of power being drawn by the load.

author: Damianos
author_rank: Frequent Contributor
timestamp: December 18, 2017, 03:50:49 pm
content: Quote from: Decoman on December 18, 2017, 11:32:07 amIf I understand correctly what you ask, the question is when there is a battery (voltage source) unconnected, if the voltage is there or not?Also, the voltage is not pushed, is the force that can do the electrical charge to be moved.Something more, the grounding is not something magical, we use it (because of the huge mass) as electrical reference...

author: Decoman
author_rank: Regular Contributor
timestamp: December 18, 2017, 05:21:46 pm
content: Hm, I think nobody understood my question here.So, when I used the word "ground" I was thinking of the ground connection found on the power cable that goes between the unit and the wall socket that is linked to ones fuse box. I was not referring to the third output on the power supply, that is labeled "ground".I was wondering if a power supply that ordinarily would be powering a circuit board if the circuit board was connected to the power supply, but if "turning on the power" without having the power supply connected to anything to be powered, I was wondering if electricity is going places inside the power supply (maybe going back to ground/earth), or, if a power supply then is simply understood as being idle where the + and - output connectors aren't touching anything.I have sometimes heard/read that "earth" is a "reference", but what does that mean? I've always thought that ground, being real ground would just suck up and lead away any current that would otherwise be harmful if not shunted off to a ground wire going down into the soil. Presumably, the earth wire would handle a maximum amount of current before disintegrating due to the heat created.

author: glarsson
author_rank: Frequent Contributor
timestamp: December 18, 2017, 05:40:30 pm
content: Quote from: Decoman on December 18, 2017, 05:21:46 pmThe ground wire in the power cable is connected to the "third output" (often green) on the power supply.Quote from: Decoman on December 18, 2017, 05:21:46 pmWhen you turn off the faucet in the kitchen the water stops flowing, it doesn't start "going places" in the house. Tension (or voltage as some say) is like water pressure. Current is like water flow.Some of the current going into the power supply is "going places" inside the power supply to power the electronics and displays, but the current that are supposed to flow between + and - through the load stops when the output is turned off or the load is disconnected. This is where the water analogy breaks down as water starts "going places" when a hose is disconnected and the water supply hasn't been turned off.

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 18, 2017, 06:05:02 pm
content: Quote from: Decoman on December 18, 2017, 11:32:07 amRemember a voltage is a potential difference. You can have a potential difference without any current, which will likely be the case for a power supply without anything connected.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 18, 2017, 06:59:31 pm
content: Quote from: Decoman on December 18, 2017, 05:21:46 pmPerhaps because you seem to have two different questions here, and based on a misunderstanding.QuoteThe "third output" on the power supply (typically a green color connector labeled "Ground" is actually CONNECTED to the ground connection on the power cord -> wall socket -> fuse box. That terminal is there for you convenience. Normally no current flows through that connection whether the circuit is powered or not, whether the power supply is turned on or off.QuoteIt is not "going places" any more than your utility mains power is "going places" when you turn out the light in your room. If you open the switch, the voltage is still there, but with no load, no current will flow.QuoteGround is used for many purposes in electricity, electronics, RF, and other fields. In electricity, its primary use is a common "reference" so that "ground" at your house is essentially the same as at the far end of the road (or way back at the generating plant). It is used as a safety circuit that conducts fault currents away from YOU so that you are not electrocuted. In this sense, the safety ground (green/yellow) wire in the power cord under normal conditions conducts NO CURRENT AT ALL. It is only there as a "safety feature" so that if there is a problem inside an electrical appliance (such as your bench power supply, etc.), any fault current will go to the green-wire safety ground and not through your body.In electronics, we use the word "ground" most often to refer to the designated reference point (0 volts) in a circuit. Regardless of whether it is connected to the crust of the planet, or whether it is in a quad-copter drone flying 100s of m above the crust of the planet. The green terminal on a bench supply is provided as a convenience. If you wish to connect your circuit to the crust of the earth, it is a simple matter of a jumper wire over to that green terminal. But, if designed properly no significant current will be flowing through that connection.If RF, especially for low frequencies, the crust of the earth is used as a "counterpoise", or essentially the "return path" of the RF signal or the other-half of a dipole antenna, etc. This is an extremely crude explanation that would be widely criticized over in the RF forum. LF and MW transmitter towers frequently have an array of wires buried in the soil around the antenna which form the counterpoise to the tower part that sticks up into the air.Ref:https://en.wikipedia.org/wiki/Counterpoise_(ground_system)

author: IanB
author_rank: Super Contributor
timestamp: December 18, 2017, 07:13:15 pm
content: Quote from: Decoman on December 18, 2017, 05:21:46 pmThis is a misunderstanding. If you connect a terminal of a battery to the ground no current will flow.The only reason mains current may flow to ground is because the ground is acting like a big "wire" making a return path back to the substation. At some point the current that flows into the ground will flow out of the ground again and back into the transformer.There is nothing magic about this, it is just about electric circuits. The ground does not "suck up" electricity.

author: Decoman
author_rank: Regular Contributor
timestamp: December 19, 2017, 06:57:42 am
content: Thank you all for your replies.I did not really think that the power supply would divert current onto the earth connection on idle, but I wasn't sure so I thought I would ask. What actually goes on inside my variable power supply isn't clear to me, but that isn't very important to me at this point in time.It did not occur to me to make a parallel between how a power supply works and how the fuse box for my apartment links to the power grid, as the power supply unit is a consumer product to be actively used and potentially abused and not being a major installation acting as a mere relay for electrical power.Quote from: IanB on December 18, 2017, 07:13:15 pmQuote from: IanB on December 18, 2017, 07:13:15 pmWow, I can see how this would be analogous to having a current necessarily flowing between two points, but to think that current going into earth would be coming back seems so weird to me. Makes me wonder if an earthed ground connection might simply fail to work as a safety measure if current then simply cannot automatically trace itself back to the power plant if the current was somehow passing though simple dirt and/or rock in the ground, OR, perhaps all earthed ground wires SIMPLY wired and going directly back to some electrical grid, like some earth connection at ones local transformer station? I guess I simply imagined that the current going through an earthed ground wire would just flow into the ground, but as pointed out, that seems to be wrong.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: December 19, 2017, 09:42:12 pm
content: There may be some strange, as yet unexplained, exceptions, such as ball lightning. Doesn't seem to appear as a complete circuit.It's going somewhere though!

author: james_s
author_rank: Super Contributor
timestamp: December 19, 2017, 10:04:10 pm
content: Your power supply will draw some current when switched on even if nothing is connected to the output. There is current circulating through the primary of the power transformer magnetizing the core and there are some losses here due to resistive heating in the wire and eddy currents in the transformer core. Then you will have the power required to operate the components within the power supply itself, this should not be much but it still exists. Forget about "ground" for a moment and think only about a potential difference between the + and - outputs. The - side of a circuit is often referred to as "ground" but that is no relation to the earth ground. The term "ground" often refers to any kind of common return path.