# 2 lead acid batteries connected in parallel

Discussion in 'The Projects Forum' started by umjorge2, Jun 4, 2015.

1. ### umjorge2 Thread Starter New Member

May 16, 2015
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If I have 2 lead acid batteries connected in parallel (both are charged) and one of the battery shorts to the other battery, what will happen to the battery being shorted to and whatever other components that are on that circuit?

2. ### crutschow Expert

Mar 14, 2008
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What do you mean "shorts to the other battery"?

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3. ### umjorge2 Thread Starter New Member

May 16, 2015
10
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Just that I guess. One battery short circuits to the other...

4. ### umjorge2 Thread Starter New Member

May 16, 2015
10
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Or maybe another way of saying it is what happens to battery 2 and components if there is a short at battery 1?

5. ### wmodavis Well-Known Member

Oct 23, 2010
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150
I don't believe you could charge a battery that is a short circuit. Your terminology is NOT clear.
What do you mean by "one of the battery shorts to the other battery"?
How do you determine that "both are charged".
Are the batteries same capacity/same internal resistance/same acid specific gravity?
What "other components that are on that circuit"?

If you place a 'short' across a circuit that has some voltage present the voltage will go to near zero depending on the resistance of the shorting element, and the current flowing through the short will increase to a value which depends on the voltage present and the resistances in the circuit. Ever heard of Kirchhoff. He was smart.

It would help immensely if you would draw a diagram so we can more fully understand and get on the same wavelength with you.

6. ### umjorge2 Thread Starter New Member

May 16, 2015
10
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It was in interview question that I'm just trying to see if I answered correctly. As best as I can remember that's how it was worded. I'm only assuming both are charged and are identical batteries. I said you would get a power surge because of a huge increase in current that would likely damage the other battery and components. The components can be anything that is on the same parallel circuit

Last edited: Jun 4, 2015
7. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
I am not sure what electrical principle you base your answer on. You might explain what you think would cause two identical fully charged batteries connected in parallel to cause a 'power surge'. Of course you never stated whether they are connected + to + & - to - or connected + to - & - to +.

My question to you is " What causes surges?" - in general that is. Then try to relate your proposed cause to the specific situation you are describing which to me I can only guess at because you have not clearly explained yourself. Assumptions are not the best thing to base something on. Either for you or for me. My crystal ball is broke.

Last edited: Jun 4, 2015
8. ### crutschow Expert

Mar 14, 2008
13,469
3,356
Basically the good battery will discharge into the shorted battery with a current equal to the battery voltage divided by the combined (series) resistance of the good battery and the "shorted" battery.

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9. ### umjorge2 Thread Starter New Member

May 16, 2015
10
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Ok I'm not trying to confuse anyone on purpose but I don't like how I'm being accused of not explaining it good enough when I'm doing my best to do so. I'm sorry I don't know how else to put it.

10. ### umjorge2 Thread Starter New Member

May 16, 2015
10
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All I was looking for. That's good enough for me thanks.

11. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
That's not good enough. Besides IMO based on only what you have stated it is simply not true. I was just trying to help you think through what you said. Not just give you my answer. Thinking based on knowledge of science is powerful. Just having someone give you a simplistic answer is not powerful. Clear communication is foundational to understanding for both the questioner and the questioned. A thick skin may also help.

12. ### umjorge2 Thread Starter New Member

May 16, 2015
10
0
What is that suppose to mean?