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DC Ground

07/30/2011 10:48 AM

what ground should I use for a simple DC circuit

Now, here's my question.

1) Is it correct that I have put the ground on negative terminal of a battery?
2) How's it working? I mean what's the essence of having that?

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Guru

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#1

Re: DC Ground

07/30/2011 11:08 AM

I'm hoping you're not working with high voltage.

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#15
In reply to #1

Re: DC Ground

08/12/2011 2:56 PM

nyuk, nyuk, nyuk...maybe...cleansing of the gene pool!

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#2

Re: DC Ground

07/30/2011 12:33 PM

"Simple DC Circuit"? A really simple circuit fed from a primary battery does not usually need an earth.

Some complex circuits - like steering gear for a ship - may deliberately avoid any earth, because an accidental earth, extra to an intended earth, could cause dangerous full rudder at the wrong moment.

Earthing a circuit makes sure it cannot gather a high voltage by electrostatic charging or by capacitance coupling to an AC supply - in most common cases it is done for safety reasons, in case a fault should connect the circuit to a dangerous voltage and the earthing is low resistance so that a supply fuse will blow or overcurrent-tripped circuit breaker open.

Mostly, the pole that is earthed is a matter of "usual practice" - there is no operational reason to use + rather than -. Perhaps, 130 years ago, Mr Edison decided to earth negative - since earthing positive would be incompatible with existing circuits, positive earth would be uncommon!

For example, 50 years ago, it was usual practice to earth the positive of a motor car battery. But then they changed to "negative earth" and now the "electrics" on an ordinary car are more complex than anything else the ordinary man uses!

Telephone battery supplies are "earthed" from the positive to avoid electrostatic charges, but usually the connection to earth is via a supplementary supply and high resistance which ensures both poles are negative to earth. The high resistance enables an earth fault - like a broken wire fallen off a bare wire circuit on wooden poles and insulators - to be detected without energising any automatic circuits. The argument for biasing all circuits negative was based on the corrosion effect of leakage currents - telephones & relays in the phone circuit used thin wire easily corroded through and failed sooner if held positive.

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#8
In reply to #2

Re: DC Ground

07/31/2011 12:50 PM

In modern cars with better grade of insulation it would not matter which polarity was grounded. But in early models the electrical insulation used rubber and cloth covered insulation and many components were mounted on wood, because of this leakage to ground was much more common.

By using the positive battery terminal as ground corrosion at these points was minimised.

Spark plugs worked better with a positive ground also, but nowadays we we can change this to the same set up with a negitive ground system.

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#9
In reply to #8

Re: DC Ground

07/31/2011 4:02 PM

I do not think the wire insulation on cars was ever a problem, rubber insulation has been available for a long time, as has the rubber tyre.

I am not an automotive specialist to know the history of the standards, but I do remember that, on the positive earth cars, the solenoid and motor coils etc were tied to negative and put on by switching the earth (some all the time, not ignition controlled - I remember a case when someone's horn stuck on - only disconnecting the battery stopped it! And I just checked my current car wiring diagram - horn is not ignition controlled). When negative earth come in, switching was moved to the live side - still in the positive. So from the corrosion (cathodic protection) point of view, all the thin wires in solenoids etc were still held negative and "best practice".

I think you are correct about spark plug polarity - but since the spark is 25 kV and battery 12 V, swapping the low tension wires fixes the polarity easily.

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#11
In reply to #8

Re: DC Ground

07/31/2011 8:55 PM

The basic reason for the change was that cars rusted less with negative earth....

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#16
In reply to #11

Re: DC Ground

08/12/2011 3:14 PM

Some old wives think that...but since the vehicle does not reference the Earth as "ground" it proves to be false.

Reference the following article:

http://mgaguru.com/mgtech/electric/et098.htm

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#3

Re: DC Ground

07/30/2011 1:06 PM

If it's a simple low voltage battery circuit there is no real need for ground, it's just a convenient reference and it stops the circuit 'floating' up due to any stray voltages, bad connections, induced currents or interferrence, however these things are usually associated with mains voltages.
After all you don't bother grounding one side of a torch (flashlight for our US readers?) do you?
Conventionally the battery negative is often ground. Sometimes it's handy to have no ground as you can then take any point as the ground connection for an ascilloscope.
Sometimes it is a great advantage to have the whole device floating, it can then take it's reference from whatever it's connected to E.G. Say it's a pre-amplifier, it's output will be connected to a power amp and the 'ground' side of the output will connect to the power amp ground at the connector (say a phono plug, inner signal, outer ground).
Del

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#4

Re: DC Ground

07/30/2011 2:31 PM

One of the essential reason to connect cabinet to ground point is, that it make testing and debugging of circuits very easy in manufacturing and in field. You just don't need to search for ground point, Connect negative point of tester or CRO to the equipment body and you can check all other test point easily.

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#10
In reply to #4

Re: DC Ground

07/31/2011 4:48 PM

Rakesh Semwal,

I do not think anyone ever connected the cabinet to ground just to make it easy to find a common test point! The original post never mentioned cabinet. Most cabinets are painted, it is not easy to make a connection to them.

Also, I think you meant "circuit common" when you wrote "ground point", which will only confuse matters for the original post question.

Perhaps this is a Ghandian method!

He was a great philosopher and politician, but not an electrician, so far as I know.

If you will be so kind as to wait an honorable moment of forbearance and forgive the levity and ignorance, who was M.L.K. ?

67model

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#5

Re: DC Ground

07/31/2011 1:45 AM

1) Is it correct that I have put the ground on negative terminal of a battery?

YES!

2) How's it working? I mean what's the essence of having that?

It is a common point for all other voltages in the circuit. For a truly DC circuit it can just be a point to point connection using a wire. If there are IC's and modulating DC voltages the wire starts to have an inductive component commonly labeled as Z or J or Jω indicating the frequency ω dependency.

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#6

Re: DC Ground

07/31/2011 7:33 AM

Firstly, say you were making a portable radio, (one without a long power lead), do you understand that it has no "ground". It only has a positive and a negative battery supply.

So your question could be rewritten to, "on what battery connection should I connect the negative?", which is usually the negative pf course! It can also be called 0 volts.

But some systems are even run "negative" and then the connections are effectively reversed......(but should still be correctly marked, so you will not know!)

Then there are electronic units that use Op Amps, some of which need a positive and a negative supply, so they might use two batteries, connected from one battery's positive, to the other battery's negative and connect the circuit 0 volts to the junction of the two batteries....

Often "0 volts" are incorrectly referred to as ground, do it myself sometimes, but in simple battery driven projects, a "real" ground is seldom needed.

Funnily enough,if a portable radio has a problem receiving some distant stations that are required, many add, via a small capacitor, a length of wire or an antenna to improve reception.

What many don't know is that quite often, the reception can be just as well improved by adding a proper ground connection (from the metal of a window frame or water pipe or similar), to the negative battery connection. I cannot guarantee that it will work in all situations, but it is often simpler to try first that, than to add an aerial.

Do not forget that the radio effectively works on the voltage difference and anchoring one supply to a real ground, simply makes the "difference" greater.....also adding a proper antenna as well, will of course make the difference even greater, even better far stations too....carefully touching each connection of the tuning cap (for radios with one!) with a finger, will usually find out that a significant change for the better in reception volume happens at some point. Do not forget the small cap for isolation purposes......something small in the Pico or Nanfarad range should do it.

Old fashioned M & LW Radios are particularly helped in this manner.

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#12
In reply to #6

Re: DC Ground

07/31/2011 11:47 PM

Very wordy, and i think you only confused him with too much information.

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#13
In reply to #12

Re: DC Ground

08/01/2011 6:57 AM

I may have confused you.......sorry if thats the case.

Go and find a simple primer to read if you are really interested in learning more....or go to another blog if you are not!!

Also let the OP also answer for himself.

I like many here answer for all at the same time......as far as possible that is.

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#17
In reply to #13

Re: DC Ground

10/09/2023 8:54 AM

<...I like many here answer for all at the same time......as far as possible that is....>

That's not true.

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#7

Re: DC Ground

07/31/2011 8:52 AM

DC ground can either be negative or positive in a simple circuit. Normally used or referred to as the common point of reference of voltage measurements in an electronic circuit. Depending on the ckt. designer's (eng'r) inclination, knowledge or expertise, the circuit's intended application and readily available electrical components, will normally guide in determining whether to use the negative or the positive side of the power supply ground...

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#14

Re: DC Ground

08/02/2011 8:44 AM

Yes, for simple DC circuits, you can connect ground to the negative terminal.

Not sure how far in to EE you are, but the reason that you NEED to connect the ground is very basic electronics. It provides a return path for the current. If you do not have it connected no current will be able to flow through your circuit, and thus it will never work. Kirchoff does a very good job at explaining this little phenomenon with his voltage and current loop equations. All current leaving the source is equivalent to all of the current returning to the source (through ground).

Sorry if this is too basic, just thought I'd help cover all possibilities since everyone else helped with the more complicated stuff haha.

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