AC/DC Adapters and Grounding - Page 1
Forum section: electronics / beginners

author: arielberschadsky
author_rank: Newbie
timestamp: March 07, 2023, 03:14:27 am
content: Why do standard AC/DC adapters for low voltage DC applications such as 5/9/12 Volts not have three prongs (hot, neutral, and ground) for insertion into the wall? Instead, they always have only two prongs (hot & neutral), and therefore make it impossible to ground the devices they are plugged into. I'm building a small electronics project that I would like to ground, and while I would find it very convenient to use a simple AC/DC adapter, it seems that if I want to ground the circuit and project box, I'm going to have to instead use a 120/12 volt AC transformer and design a full wave bridge rectifier circuit, just so that I can get access to the grounding pin from the wall.

author: mariush
author_rank: Super Contributor
timestamp: March 07, 2023, 04:58:18 am
content: Due to how the high switching frequency transformer is designed, and how its wires are insulated, you often don't need ground.Using a classic transformer and bridge rectifier is not your only option.There are power supplies - for example laptop power adapter style supplies - you can buy which will have ground pin...There are small ac-dc converters (like wallwarts/laptop adapters but without housing and with mounting holes) you can buy and insert/attach to your productBut even so, you should consider that buyer of your product may plug your product into a mains socket without grounding. Either check for that and make your product refuse to work, or redesign your product to not need grounding.

author: CountChocula
author_rank: Unknown
timestamp: March 07, 2023, 05:07:41 am
content: You can find power supplies that are earthed (example)—the output itself may not be referenced to mains earth, but the earth conductor does carry into the power supply, so you could grab it from there and take it to your project. Alternatively, you could mount a standard IEC outlet on your project's enclosure, use the earth connection for your purposes, and then use a chassis-mounted switching power supply inside the project.

author: Zero999
author_rank: Super Contributor
timestamp: March 07, 2023, 02:29:49 pm
content: Quote from: arielberschadsky on March 07, 2023, 03:14:27 amWhy?

author: Brianf
author_rank: Regular Contributor
timestamp: March 07, 2023, 02:31:25 pm
content: I've certainly got adaptors here where the output 0V is connected to Earth on the mains connector. They are 'laptop' style, with an IEC C14 input, rather than 'wall warts'.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 07, 2023, 03:30:55 pm
content: These adaptors are "double insulated" to avoid having an earth pin.Avoid using these if you need real grounding for safety and/ or signal integrity reasons.If you need a ground, there's no benefit to be had by swapping a double insulated linear for a double insulated smps.

author: arielberschadsky
author_rank: Newbie
timestamp: March 07, 2023, 06:33:06 pm
content: ESD control. I want to be able to ground the metal case to permit static discharge right to ground through the case.

author: tooki
author_rank: Super Contributor
timestamp: March 07, 2023, 06:53:02 pm
content: Quote from: arielberschadsky on March 07, 2023, 03:14:27 amOr you could use an internal power supply module. Or you could just provide a grounding connector independent of the AC adapter, like the banana jack found on many soldering stations. Then you can ground that to whatever.

author: Zero999
author_rank: Super Contributor
timestamp: March 08, 2023, 08:31:13 am
content: Quote from: arielberschadsky on March 07, 2023, 06:33:06 pmWhat makes you believe that will help?The metal case acts like a Faraday cage. It will still do that, whether earthed or not.If the case is accumulating static charge, then you don't want a direct connection to earth. A 1M resistor is typically used.

author: EPAIII
author_rank: Super Contributor
timestamp: March 08, 2023, 11:33:00 am
content: Since I have joined this group and others devoted to electronics and computers, I have noticed a lot of concern about grounds and ground connections. Far more then I ever worried about in over 45 years of professional electronic design, installation, modification, and maintenance/repair.Some facts:1. The concept of a ground in an electronic circuit (and SOME, not most electric circuits) is it is simply a convenient and MOSTLY ARBITRARY reference level from which the other Voltages in a circuit are measured. The most important word in my last sentence is "ARBITRARY". Consider a project made with wood, perhaps a simple box. The box has adefinite length, width, and height. But where is the ZERO point? At the top? At the bottom? Left? Right? Center? WHERE? In truth, there is no real, intrinsic zero point. The plans may have one that the artist choose, but he/she could have chosen any one of a number of others and the table would still look and work the same. It would still be the exact same size.The exact same thing applies to electronic circuits. There may be Voltage differences between different points, but there is no intrinsic zero Voltage. Oh, you might define one as a point where the positive and negative charges are present in equal numbers, but just how are you going to find or, more importantly, MAKE that point in the real world. Does even the earth, as a whole, have the same numbers of + and - charges? I am not aware of anyone who has ever made such a measurement. And what about local differences? Many natural processes can produce an excess of one or the other.From a practical point of view, you can not produce nor even measure the presence of a "true" point of zero charge.2. There is a reason for the ground connection in the AC power outlets in building in most countries. And that reason is protection against dangers like fire and loss of human life. In other words, protection against shocks to people and dangerous currents that could melt the conductors in the buildings' walls, causing fires - which cold also cause loss of human life. The ground wire is connected to an "earth ground" (that's where the name "ground" comes from) and it provides a very dependable return path for any stray current that may exist in a circuit. So if a conductor should come into contact with the external, conductive shell of a device, then a heavy current will flow in that conductor and back to the pole transformer, which also is grounded. And this heavy current will act to quickly trip the fuse or circuit breaker, disconnecting that defective circuit from the power grid. No current means no shock and no melting wires that set the building on fire. In one word, SAFETY. And the ground connection is called a SAFETY ground.That is the purpose of the ground wire in a connection to the building's power grid, not any of your circuit design goals. And, from years, decades of working with video and audio circuits, I can personally attest to the FACT that those power circuit grounds are really poor at helping any circuit problems.3. "Wall Wart" style power supplies, for the most part, do not connect to the SAFETY ground in the buildings' power connections. WHY? Because the industry, which is in a never ending search for less expensive ways of doing things, has lobbied for an alternative to that method of keeping the users safe from shock and fire. This is called double insulation and current limiting. The wall wart power supplies incorporate both of these technologies and, even together, they cost less than having a third, ground conductor. They have at least two layers of insulation that can each ensure against shock. The outer, plastic case is one of those insulation layers and something on the inside is the second, probably the varnish insulation on the transformer wire or an insulated circuit board or something that the inspection/certification body accepted. Current limiting is provided by something like a simple fuse or current limiting wire. Door bell transformers have had such inexpensive devices for many decades now. And since that is less expensive than the extra copper conductor, that is how it is done. Next time you look for a lower price, blame yourself.So the "wall wart" style power supplies are an exception to the need for a SAFETY ground connection in most countries.4. MOST electronic circuits do not really need a real "earth" ground. Things like modern automobiles and other vehicles have all manner of electronic and computer circuits in them and yet they are separated from the actual earth by four rubber tires. And if that is not enough, those tires usually roll on asphalt or concrete road surfaces, both pretty good insulators. Those cars are not grounded. Yet they work. Airplanes are another example. They also have tons of electronics and can be miles/km up in the air. No "ground" wires hang from their tails. Yet they work. The simple fact is, an actual "earth" ground is not really needed and, in most cases, can be omitted with NO DETRIMENTAL effects on the operation of the electronics in those devices.Anyone who has worked in electronics for any amount of time knows this. Oh, sure there are cases where an earth ground is essential. An AM radio antenna is one such case. The "earth" ground forms a conductive mirror for the tower which is effectively only 1/2 of the actual antenna. AM broadcast frequencies being what they are (~1Mhz), that ground plane needs to extend for hundreds of feet (meters) from the base of the tower in all directions. But that need disappears with FM radio and higher carrier frequencies. Even pocket AM radio receivers do not need actual "earth" ground connections.Most outdoor electronic devices are grounded for protection against lightning strikes, not for performance. And most indoor electronic devices do not need it at all except for safety considerations. And the wall wart power supplies take care of that need in other ways, as I have explained.I wish I could somehow communicate this to all newbees in the electronic field. I am sure the "experts" here are going to come up with a million exceptional cases. But the real experts, who design our cars, planes, and so many other electronic devices, will know of what I speak. Newbees in electronics would be much better served by learning more about Ohms law. Seriously! It is far, FAR more useful than "earth" grounds.In the words of the immortal bard, "Much Ado About Nothing."

author: EPAIII
author_rank: Super Contributor
timestamp: March 08, 2023, 11:52:35 am
content: One more point to add to my rant above.OBTAINING a good, low resistance, earth ground is not a trivial endeavor. Believe me, I have tried. A simple, copper clad rod depends a lot on the soil condition. Dry soil is not a very good conductor and it can take many feet/meters of that copper rod to get down even to under ten Ohms. AM radio stations bury thousands of feet of copper wire - not copper clad, but all copper wire and not just any gauge you can find in a neighborhood home supply. Wire the size of your thumb, measured in the number of "oughts" (zeros). A single joint can take a whole pound of solder.One station where I worked had a 20 foot section of the copper outer conductor of 3" solid coax sunk into the shore of a salt water bay.And even with extreme measures like those, you wonder about the actual effectiveness of the ground connection.These are the kinds of installations that are made when a good, "earth" ground is really necessary. Not a simple, copper clad rod driven into the ground near the point where power enters the building and conveyed from there with the MINIMUM size conductor needed to last longer (before melting) than the main breaker if a short is encounters.When you newbees talk about "earth" grounds, you are simply daydreaming about connections that do not and can not exist without hundreds or thousands of USDs being invested in them.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 08, 2023, 06:38:28 pm
content: Ground has become too much of a catch all. We ask it to act as reference, shield, protection and return conductor and do it all at without complaint.It’s worth a ranting about and sharing the pain and lessons learned.A good knowledge of grounding, bonding and shielding is essential in the ee world.Thoughtless application of the green wires will lead to project fails, erroneous measurement, smoke and shocking situations.And no, you can't fix it in code!

author: Brianf
author_rank: Regular Contributor
timestamp: March 08, 2023, 07:38:22 pm
content: Quote from: EPAIII on March 08, 2023, 11:52:35 amMeasured from where to where?

author: Brianf
author_rank: Regular Contributor
timestamp: March 08, 2023, 07:39:27 pm
content: Quote from: Terry Bites on March 08, 2023, 06:38:28 pmBut absent in may of the posts on here.

author: Zero999
author_rank: Super Contributor
timestamp: March 08, 2023, 08:55:13 pm
content: Quote from: Brianf on March 08, 2023, 07:38:22 pmGood point and quite funny considering the rant. I presume he meant with respect to mains earth.Earthing for safety is really about ensuring all exposed conductive surfaces do not have a dangerous voltage relative to one another.