Meaning of BATERRY polarity

[lefam]

Hi guys!

I am pretty new to electronics. I am having some problems with my first circuits and I am now suspecting that maybe my understanding of battery polarity is wrong.

So, my question is: in batteries (example 9V alkaline) the (+) terminal is +Vs, and the (-) terminal is GROUND?

(+) terminal = +Vcc?
(-) terminal = GROUND?

I have been using (-) like +Vs and (+) like GROUND. Probably the cause of failure in my first circuits.

 

[BrownOut]

In circuits with bipolar components, the "+" terminal of the battery is VCC, and the "-" terminal is ground. Looks like you had it backwards.

 

[lefam]

So, to power a circuit (for example the 555 IC), what should I connect where they ask for +Vs (PIN8 in the case of the 555 IC)? The (+) terminal from the battery or the (-) terminal?

 

[BrownOut]

You should have a VCC or V+ pin that connects to the "+" terminal of your battery. I don't know about a +Vs pin.

PS: Pin 8 connects to the "+" terminal for a 555.

 

[3v0]

Voltage is always measured between two points. We can illustrate this with a volt meter which has a black probe and a red probe. By convention the black probe it though of as gnd.

If we touch the black prove to a - on a cell and the red to + we will read 1.5V. If we reverse the leads with the black/gnd probe on the + we read -1.5V.

This illustrates that in electronics gnd is something we assign (lets not think about house wiring). When we pick the - terminal for our gnd we seen a positive voltage. When we pick the + as gnd we see a negative voltage.

So if you want to provide a positive voltage to your circuit use the - bat terminal as gnd and the + to the voltage input that is marked with one of +, VCC, VDD, ...

 

[crutschow]

Often "common" is used for the common connection on circuits (the point to which all voltages are referenced) and "ground" is used for an actual connection to earth. But when ground (gnd) is referenced in a circuit it usually refers to common rather then earth.

 

[lefam]

So, that's why my circuits where not working (because of using - terminal as +V). I tried to build a 555 LED flasher and it was not working. I failed also with transistors.
Now my transistor circuits are working.

I have one curiosity: why do the electrons flow from the (+) terminal to (-) in the battery? Are they following the conventional flow? I am confused because in electron flow (the real flow) electrons flow from (-) to (+). What is the meaning of polarity of batteries?

 

[BrownOut]

Electrons flow form - to +
Conventional current flows from + to -
These two concepts of current flow are equally ligitimate and complimentary.

Dont' think about it too much. You'll understand current flow in time. For now, just concentrate on getting the correct terminals connected to the correct pins.

 

[crutschow]

I have one curiosity: why do the electrons flow from the (+) terminal to (-) in the battery? Are they following the conventional flow? I am confused because in electron flow (the real flow) electrons flow from (-) to (+). What is the meaning of polarity of batteries?

Electrons flow externally from the (-) terminal to the (+) terminal in a battery, and the conventional current flow is from the (+) terminal to the (-) terminal.

Perhaps you are confused by the fact that internal current flow through the battery is from negative to positive, but current flow through the attached components is from positive to negative. That is because the battery provides the electromotive force that initiates the flow of current.

The meaning of polarity in batteries is the same as polarity in any circuit element. The positive (+) terminal has a higher potential than the negative (-) terminal.

 

[Dakta]

A funny way of looking at it is described in a book I bought, very old 'Starting electronics' (25p local carboot, ten years ago and it was old even then).

I don't know if it'l ring with those in the know but it describes it like this:

'if you think about it, negative flow in one direction is the same as positive flow in the other'

An alternative look at it:

Conventional Current vs. Electron Flow

On my travels to find a really good definition, it seems this is one of those wacky things in electronics, where a mistake was made and it was easier to not fix, which is why we get the confusion between electron current and conventional current.

If you fancy more reading:

Conventional vs Electron Flow

The way I see it, if you put a shopping bag on a set of weighing scales that weights 20kg, then take away a bag of sugar weighing 1kg...

So what have you done, have you added -1kg or have you just removed 1kg?

As you see, it actually makes no difference, just alters the way you look at it. Current flow is current flow, but circuits generally work with conventional flow, i.e positive to negative, as they originally thought it did.

 

[crutschow]

On my travels to find a really good definition, it seems this is one of those wacky things in electronics, where a mistake was made and it was easier to not fix, which is why we get the confusion between electron current and conventional current.

The "mistake" was that the definition of the charge polarity of the carriers was arbitrarily taken to be "positive" and the current flow as positive to negative before anyone was able to measure what the actual charge of the carrier of electricity was. After it was determined the charge carrier was negative (such as by experiments with cathode ray tubes), it was too late to change the definition of current flow.

 

[3v0]

I used to think we understood current even with two ways of looking at it. But with the advent of dark matter and energy, string theory and membranes, WIMPs etc, I have grave doubts about calling anything more then a theory or convention.

 

[Dakta]

The "mistake" was that the definition of the charge polarity of the carriers was arbitrarily taken to be "positive" and the current flow as positive to negative before anyone was able to measure what the actual charge of the carrier of electricity was. After it was determined the charge carrier was negative (such as by experiments with cathode ray tubes), it was too late to change the definition of current flow.

Yep that's as I understood it.

 

[lefam]

Electrons flow externally from the (-) terminal to the (+) terminal in a battery, and the conventional current flow is from the (+) terminal to the (-) terminal.

Perhaps you are confused by the fact that internal current flow through the battery is from negative to positive, but current flow through the attached components is from positive to negative. That is because the battery provides the electromotive force that initiates the flow of current.

The meaning of polarity in batteries is the same as polarity in any circuit element. The positive (+) terminal has a higher potential than the negative (-) terminal.

Thank you guys.
I understood.

 

[lefam]

Thank you guys