Connecting batteries in parallel

[fterh]

I understand that connecting identical batteries in parallel will increase the overall battery's capacity. But what about:

 

1) If the batteries aren't identical? Say one is 2V, and the other is 4V. What will happen? Is there an equation to calculate overall emf?

 

2) If the batteries do not have negligible internal resistance? That is to say, e.g. each battery have internal resistance of 1 ohm. If you connect two of them (identical) in parallel, the overall resistance of the battery will become 0.5 ohm. So does the current in the circuit increase due to decreased overall resistance?

[Mr Skeptic]

I understand that connecting identical batteries in parallel will increase the overall battery's capacity. But what about:

 

1) If the batteries aren't identical? Say one is 2V, and the other is 4V. What will happen? Is there an equation to calculate overall emf?

 

It would depend on the resistance of the battery (or if you prefer how many amps it can provide).

 

2) If the batteries do not have negligible internal resistance? That is to say, e.g. each battery have internal resistance of 1 ohm. If you connect two of them (identical) in parallel, the overall resistance of the battery will become 0.5 ohm. So does the current in the circuit increase due to decreased overall resistance?

 

Yes, two identical batteries in parallel have half the resistance and so double the current, quite what people expect.

[TonyMcC]

It would depend on the resistance of the battery (or if you prefer how many amps it can provide).

 

 

 

Yes, two identical batteries in parallel have half the resistance and so double the current, quite what people expect.

 

Two identical batteries would produce twice the SHORT CIRCUIT current. If connected to a load resistance this effect is much reduced. If the load is large compared to battery internal resistance the additional current through the load may be negligible for practical purposes.

[fterh]

It would depend on the resistance of the battery (or if you prefer how many amps it can provide).

 

 

 

Yes, two identical batteries in parallel have half the resistance and so double the current, quite what people expect.

 

Yeah I get what you mean Sort of.

[ewmon]

I understand that connecting identical batteries in parallel will increase the overall battery's capacity. But what about:

 

1) If the batteries aren't identical? Say one is 2V, and the other is 4V. What will happen? Is there an equation to calculate overall emf?

 

2) If the batteries do not have negligible internal resistance? That is to say, e.g. each battery have internal resistance of 1 ohm. If you connect two of them (identical) in parallel, the overall resistance of the battery will become 0.5 ohm. So does the current in the circuit increase due to decreased overall resistance?

 

1) The 4V battery would run current backwards through the 2V battery. The initial voltage of the this parallel arrangement will be 4V.

 

2.1) The currents add in parallel arrangements of identical batteries because Kirchhoff's Current Law says the currents flowing out of a node equals the currents flowing into it.

 

2.2) The current flowing through the circuit (including the battery pack) equals the battery pack's voltage divided by the total resistance of the circuit (including the resistance of the battery pack of 0.5 ohms). Due to the parallel arrangement and Kirchhoff's Current Law, the current splits equally among the batteries, thus each battery experiences half the circuit's current.

[dalemiller]

I understand that connecting identical batteries in parallel will increase the overall battery's capacity. But what about:

 

1) If the batteries aren't identical? Say one is 2V, and the other is 4V. What will happen? Is there an equation to calculate overall emf?

 

2) If the batteries do not have negligible internal resistance? That is to say, e.g. each battery have internal resistance of 1 ohm. If you connect two of them (identical) in parallel, the overall resistance of the battery will become 0.5 ohm. So does the current in the circuit increase due to decreased overall resistance?

 

Golly, don't ask scientists if you want a straight answer.

1) Don't connect batteries of different voltages together in parallel.

2) If you are talking about little batteries that you can hold in your hand, they can maybe handle 1000 Ohms for a little while, but they will be dead tomorrow. Hence the determining factor is the load resistance, and if you hook up to 10,000 Ohms for instance, two parallel batteries won't make any significant difference on what the current value is. Just about the same current will flow, but for about twice as long. The guy was right who said the short circuit current would double, but a short circuit would reduce the life of both batteries to minutes or seconds. If you are talking about bigger batteries, please let me talk to your guardians.