Why does a battery need to be in a circuit loop to work? - Page 1
Forum section: electronics / beginners

author: roogadget
author_rank: Contributor
timestamp: September 28, 2018, 11:34:28 am
content: This is a simple one that I don't get.Why can't I connect the positive terminal of one 12V battery to the negative terminal of another 12V battery?Why does it need to be in a loop?

author: 6PTsocket
author_rank: Regular Contributor
timestamp: September 28, 2018, 11:47:47 am
content: Quote from: roogadget on September 28, 2018, 11:34:28 amWhat do you mean by "work"? Because of the potential difference between the terminals, if you connect a device across it current flows through it. That is your loop. If nothing is connected there is no flow. Batteries can be daisy chained (wired in series) plus to minus for higher voltage. I am not sure I am clearing up what is confusing you.Sent from my SM-G900V using Tapatalk

author: roogadget
author_rank: Contributor
timestamp: September 28, 2018, 12:08:09 pm
content: I was confused about why it needs to be in a loop.By "work", I mean current flowing from one terminal to another.After reading more online about uniform electric fields and electric potential. I've come to a better understanding now.The loop is required to maintain the electric field required for current to flow.https://www.physicsclassroom.com/class/circuits/Lesson-1/Electric-Potential-DifferenceThanks!

author: Keosintal
author_rank: Contributor
timestamp: September 28, 2018, 01:02:52 pm
content: I understand what you're trying to say. It's like connecting two AAs in series. The +ve of battery 1 touching the -ve of battery 2, but they don't short circuit. Am I right?

author: roogadget
author_rank: Contributor
timestamp: September 28, 2018, 01:35:07 pm
content: correct

author: LukeB
author_rank: Contributor
timestamp: September 28, 2018, 01:44:47 pm
content: I dont have time to explain now but google redox reactions and that will explain why you need both sides. It requires a transfer of electrons between chemicals. One gives and the other receives. You cant give an electron if no one wants it.

author: rstofer
author_rank: Super Contributor
timestamp: September 28, 2018, 01:57:14 pm
content: A hint is in the word 'circuit' meaning all the way around.I don't usually bother with the concepts of fields, drift velocity, holes and such. I just think in terms of electrons running around a circuit and I completely ignore the more advanced ideas. They're not usually necessary for the discussion.You can go a long way in this field with just a few rules: Ohm's Law, Thevenin's Theorem, Kirchhoff's Laws and Norton's Theorem. The works of Volta and Watt plus a long list of other luminaries are obviously included.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 28, 2018, 09:46:11 pm
content: Actually a 12 volt auto battery already has 6 batteries (or more correctly, 6 cells) connected in series and you are just adding 6 more cells.If you have a 12 volt or a 24 volt battery without a load connected, there is no circuit. Look at it as a light in your house. If the switch is open, or off, there is no circuit, no current flow, and your light is off. If you flip the switch on, you complete the circuit, current can flow, and the light goes on.Oops, error in number of cells.

author: Bratster
author_rank: Frequent Contributor
timestamp: September 28, 2018, 09:53:37 pm
content: Not to nitpick, but 12-volt lead-acid batteries are actually made up of six cells connected in series internally.Sent from my Fi Moto x4 using Tapatalk

author: ArthurDent
author_rank: Super Contributor
timestamp: September 28, 2018, 10:03:33 pm
content: Bratster - "...12-volt lead-acid batteries are actually made up of six cells...".I know that but I don't know what I was thinking of when I typed 3.Thanks for noticing my error, which I corrected.

author: IanB
author_rank: Super Contributor
timestamp: September 28, 2018, 10:08:20 pm
content: Quote from: roogadget on September 28, 2018, 11:34:28 amImagine cars going round and round a race track. They can go round and round forever as long as they have fuel.But if you build a brick wall across the track the cars can only go round it once and then they have to stop because the wall is in the way.It's the same with electricity. If there is no loop to go around it will stop because there is no path to continue.

author: bson
author_rank: Unknown
timestamp: September 28, 2018, 10:34:25 pm
content: Think of the chemical energy in a battery as a compressed spring, which exerts a force similar to the electromotive force (electric potential). A compressed spring can't uncompress itself into another compressed spring. A battery "uncompresses" its chemical energy through a flow of charge between its terminals - in effect the near zero conductance of the air between the terminal keeps it charged, and only by closing a circuit between them with a high conductance will you permit it to release its energy. It compresses, or charges, with a current in the opposite direction. Without a conductor to permit a current all you can do is combine potentials - like stacking two compressed springs.

author: Brumby
author_rank: Unknown
timestamp: September 29, 2018, 04:49:14 am
content: There are two issues in your question. The first is current path, which addresses whether a currentcanflow. The second is potential (pressure) difference, which addressesifit will flow.Using the water analogy - think of each battery as a tank holding water ... and to make the analogy clearer, we will say these tanks are sealed.Now, connect one pipe between the tanks. Will any water flow? Answer: No. The reason why has nothing to do with any pressures involved - just that the water cannot go anywhere. It's only when a second pipe is connected that you have a path for water tobe ableto flow - and if it flows, it flows around a loop.The second part relates to potential difference - and your implied thinking that the positive on one battery has a potential higher than the negative of the other is quite wrong, unless they are both referenced to (have a connection to) a common point - which they aren't.Without a connection to a common point, every source of electricity (let's exclude electrostatic) is what is called "floating". This is what allows you to stack six 1.5V batteries to get 9V - or two floating power 12V power supplies to give you +/- 12V rails.