# What happens when non-equal voltages are put in parallel? [duplicate]

If two batteries, say 2 volts and 5 volts, are connected in parallel, are there any problems? The higher voltage will then want to flow out, but also towards the lower 2 volt battery end, right?

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## marked as duplicate by Alfred Centauri, Waffle's Crazy Peanut, Ben Crowell, Qmechanic♦May 23 '13 at 20:04

Voltage doesn't flow. Current flows. This is essentially just a short circuit. If you're talking about batteries that are assumed to be idealized voltage sources, then this is one of those questions like, "Can God make a rock so heavy that He can't move it?" A simpler question that raises the same issues is what happens when you short across an ideal voltage source with a perfectly conducting wire. If these are non-idealized batteries, you could probably get a variety of effects depending on the batteries' internal resistances, their electrochemistry, and other factors. – Ben Crowell May 23 '13 at 3:27

In reality you are not able to connect anything in parallel. There are always resistances and (for AC) capacitances and inductances that cause voltage drops. So connecting two sources will cause current flow from one battery with higher voltage to the other making a voltage drop on the wire. This current can be very high, but it is never infinite, as it would be if the resistance is zero, theoretically in Ohm's law I = U / R which leads to infinity if R = 0. For DC circuits it is also important to include C and L in transient analysis.

If resistance is almost zero, high current flow probably will cause thermal destruction of the wire and thus disconnecting two sources. If not, and they are batteries or capacitors their charges in steady state will be the same. What will happen with voltages might depend on their internal construction. You may imagine this if you would connect two sources in parallel using a superconductor.

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Firstly, I am assuming these batteries to be DC, otherwise this solution is wrong:

If you connect multiple batteries to a circuit, their polarity makes all the difference. If they are opposite in polarity then the battery with lower voltage will charge. A diagram will help to elaborate the question if you are talking about a specific arrangement.

If the batteries are of same polarity, then neither will charge. The detailed solution can be attempted by Kirchoff's loop and junction law. These laws are helpful in parallel connections mainly...

Hope it helps!

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The junction rule isn't going to be relevant, because there are no junctions (except in the trivial sense that constancy of current around a single-loop circuit can be considered to be an application of the junction rule). – Ben Crowell May 23 '13 at 3:33
well, as I previously said, that depends a lot on what the actual figure is...if there are 2-3 parallel loops, the current variables will be established accordingly – Saurabh Raje May 23 '13 at 9:54