Push or Pull Electricity.

SKiTLz · 11-23-2007, 09:12 PM

While this may sound stupid It's something i don't understand..

In elecrticity is it a push or pull flow? What i mean is..

I've got 5 X 12V Cables Running into a Terminal Strip. I have 1 cable out.

Is the device at the end of that cable going to PULL just what it needs or are those 5 cables going to PUSH more than it can handle.

Yes it may sound dumb but my electronic skills.. Well.. SUCK. :d

h3rk · 11-23-2007, 09:48 PM

remember there is no "at the end of the cable" per se, it loops back to the source through ground. Voltage at the source (actually the difference in voltage between the source and ground) tends to push current.
If you connected a million cables from terminal to terminal on the battery, something like infinate amps would flow, the cables, offer little to no resistance to current flow (due to such a large cross sectional area).
So current in a circuit is determined not only by the voltage but by this resistance as well. Thus, ohms law (variation) I = E/R.
So from that you can see that the load, or what your hooking up at the end, determines current flow, no matter how many cables you hook up to it.
Voltage pushes, loads allow current to pass (and determine how much given a particular voltage).
Cables just need to be chosen so that the current the load wants wont be to much for them.

EDIT: But technically, to fully answer the actual question, + pushes, - (ground) pulls, (equally) and loads resist. The device will allow just what it needs if it's working right, no matter how big or how many cables you have going to it. Too much is ok (cables that is, not voltage).

I bet I'll hear about electron-flow now. But I was just trying to not be too confusing, so I stayed with the hole-flow convention.

v8 scimitar · 11-24-2007, 08:28 AM

That lot was confusing to me and I am an electrical engineer!!

Think of it as water, the + is the mains water and the drain is the - along with the pipes being the cables.
You can now think of the tap as being a resistor, the more closed the tap the higher the resistance and the less current/water will flow.

h3rk · 11-24-2007, 08:33 AM

Sorry. I never was very good in english class.

eastvolt · 11-24-2007, 09:10 AM

yep, water is the best way to explain it . . .

Current = water flow
Voltage = water pressure

Curiosity · 11-24-2007, 11:16 AM

Actually, atoms have 7 electrons and when you introduce an atom on one end that has 8 and on the other end one that has 6, they all shift over to equalize. You need both sides for it to happen.

The important thing is to have a big enough wire to supply the load otherwise it becomes a fuse. Anything larger than required will still only supply what's required.

nobb · 11-24-2007, 11:50 AM

Well in reality, electricity is the flow of negative electrons, so current really flows from - to +. But electrical engineers like to use conventional flow where they treat the current as going from + to -. So when you attach those peripherals to the +12 volt lines, in reality the peripherals can be thought of as pulling electrons from the negative ground terminal and pushing them back out of the +12v terminal. On paper however, most engineers usually draw conventional current, where the current is going from the +12v to ground. It doesnt really matter which direction you draw the current as going, as long as you stick to that same convention throughout your calculations and you will get the same answer.

h3rk · 11-24-2007, 12:11 PM

I knew it.

FusionFanatic · 11-24-2007, 12:22 PM

Quote: Originally Posted by h3rk

Quote: Originally Posted by nobb

Quote: Originally Posted by h3rk

I bet I'll hear about electron-flow now. But I was just trying to not be too confusing

Well in reality, electricity is the flow of negative electrons, so current really flows from - to +

I knew it.

haha

v8 scimitar · 11-24-2007, 01:08 PM

Your all wrong as everybody knows electricity is really made of smoke and not electrons!!! If this wasn't the case then letting the smoke out of electronic circuits wouldn't make any difference and it would still work

ldiamond · 11-24-2007, 01:35 PM

V = Ri, thats pretty much all you need. The current will flow from +V to -V (Current being the positive flow, the electrons are actually moving to the opposite direction, but this is irrelevant to you). The current will depend on the resistance of the unit and the input voltage. You will burn the unit if you provide more voltage it can handle.

Voltage = Resistance * current.

JC-S60 · 11-24-2007, 03:46 PM

Quote: Originally Posted by SKiTLz

While this may sound stupid It's something i don't understand..

In elecrticity is it a push or pull flow? What i mean is..

I've got 5 X 12V Cables Running into a Terminal Strip. I have 1 cable out.

Is the device at the end of that cable going to PULL just what it needs or are those 5 cables going to PUSH more than it can handle.

Yes it may sound dumb but my electronic skills.. Well.. SUCK. :d

Usually, the one cable running to the terminal is the largest, going to the power source (neg or pos). The smaller cables are going to devices, who are in turn connected to the other pole of the power source - maybe via another power block, maybe directly to the chassis of the car (neg pole).

Now, as we assume you use components made for the car (amps, power supplies, caps, active crossovers etc...), all expect 12v. The car provides 12v, so voltage can be left out of the equation.
What is left? Power draw, shown in amps (A). This is a result of the internal resistance of the device, but we don't need to calculate that as we usually have the specs (otherwise, look at a device's fuse - it won't consume more that what the fuse is rated).

Each device should have a complete path to both poles (pos and neg) of the power source that can handle the power needed by the device.
If you have 2 devices hooked up to one cable, the cable should be able to support the sum of power needed by both devices.

So in your case, you can say the device "pulls" the power through both poles, and if the cables running to the power source (battery) aren't big enough, the will get hot, melt or burn. If they are "too big", you'll be fine.

Visualize your power consuming device (an amp for example) as a bar of lead (the weight representing the power consumption), your cabling as chains hooked up to both ends of the bar (one side neg, one side pos). Now you hang your bar horizontally by the chains which are in turn attached to 2 hooks in the ceiling (battery).

The heavier the bar, the bigger the chains and the hooks need to be, but if you have chains or hooks that are stronger than needed, it won't hurt.

I should be a teacher

Good luck!
Joachim

Curiosity · 11-24-2007, 04:31 PM

Quote: Originally Posted by v8 scimitar

Your all wrong as everybody knows electricity is really made of smoke and not electrons!!! If this wasn't the case then letting the smoke out of electronic circuits wouldn't make any difference and it would still work

And the smoke is bright red but it turns black when it hits the air. That's why you see a red glow just before it reaches the surface.