# 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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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 at 3:27

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

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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