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Anonymous Mon 16 Dec 01:05:59 2019 No.11229227 View Reply Original Report

Quoted By: >>11229248 >>11229256 >>11229312 >>11230241

electronics noob here.
what is ground? from the way it was taught in school it seamed like ground was always literally the earthing in your home power line. but what about devices that have a DC connector? surely there is no ground wire there?
and what about devices that run on battery that are not connected to anything? what is ground there?

Anonymous

Anonymous Mon 16 Dec 2019 01:19:40 No.11229248 Report

Quoted By: >>11229263

>>11229227
ground is an arbitrary reference voltage. if we charged the entire earth up to 20V, all our devices that relied on batteries and earth grounds (but not “space grounds” or anything else like that) it would not affect those electronics at all. this is an example of gauge invariance—if you take all voltages in your circuit diagrams and add the same constant voltage to everything, nothing changes.

in practice you need to think about different grounds like earth ground, chassis ground, and logic ground, because those different grounds are kept separate for a reason. but ideally a perfect earth ground could work for any ground. the different grounds are just kept separate to make sure you have separate reference voltages because conventional earth ground is actually not a perfect idealized thing. for example if you have very high power electrical devices, they can overwhelm the standard “stick a deep wire into the ground and assume it absorbs all current with zero resistance” and can e.g. melt that wire (this has happened on some electric train systems). so if you want your computer to keep functioning if that is a danger, you cordon off a special logic ground that might float relative to earth ground if you want to make sure your computer keeps working if you melt your long buried wire

Anonymous

Anonymous Mon 16 Dec 2019 01:24:49 No.11229256 Report

Quoted By:

>>11229227
Ground is the blue wire

Anonymous

Anonymous Mon 16 Dec 2019 01:27:59 No.11229263 Report

Quoted By: >>11229300

>>11229248
thanks for explaining, makes a bit more sense now.

when talking about chassis ground, does it mean that the whole device can have a ground voltage that is higher than earth ground?

Anonymous

Anonymous Mon 16 Dec 2019 01:45:51 No.11229300 Report

Quoted By: >>11229302

>>11229263
yes, basically. chassis ground is usually viewed as not as reliable as an earth ground because if something grounded to the chassis is spitting lots of current into it, then it might very well affect other things grounded to chassis, and thus screw them up. but, for example, back to the train analogy, if your earth ground has an epic failure then it might be good to have a separate chassis ground for certain devices during such a failure mode, provided you are reasonably confident that whatever is grounded to it will cause the afformentioned possible issues

Anonymous

Anonymous Mon 16 Dec 2019 01:47:26 No.11229302 Report

Quoted By:

>>11229300
*will not
not "will"

Anonymous

Anonymous Mon 16 Dec 2019 01:53:30 No.11229312 Report

Quoted By: >>11229317

>>11229227
ground = 0v to make maths/thoughts easier just like centering the cartesian plane at (0,0), voltage is just a differing charge distribution (so a higher density of electrons at one point than another). you probably know this already but helps to exhume sometimes

Anonymous

Anonymous Mon 16 Dec 2019 01:56:32 No.11229317 Report

Quoted By:

>>11229312
in electronics the actual "density of electrons" is a misnomer. you should make sure to mention that the vast vast majority of electrons are paired to positive charges that cancel them out, and you are talking about extremely tiny changes in density of "unpaired" electrons

in fact that picture is pretty much wrong anyhow, since there are things like superconductors and josephson junctions that have currents and potential differences regardless of the density of electrons

Anonymous

Anonymous Mon 16 Dec 2019 13:28:48 No.11230241 Report

Quoted By:

>>11229227
You can see it as something the energy can run into once it does its work.

Same reason why trams need only one wire (as the energy can run to the rails) but trolleys need two (as the rubber wheels act as insulation, so you need another wire to get the electricity out.

In alternating current, the two may seem to be interchangeable, but when you touch the phase, you get shocked, when you touch the ground, nothing happens.

Anonymous

Anonymous Mon 16 Dec 2019 13:29:51 No.11230244 Report

Quoted By:

You can see it as something the energy can run into once it does its work.

Basically reason why trams need only one wire (as the energy can run to the rails) but trolleys need two (as the rubber wheels act as insulation, so you need another wire to get the electricity out.

In alternating current, the two may seem to be interchangeable, but when you touch the phase, you get shocked, when you touch the ground, nothing happens.

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