Two Parallel Voltage sources and KVL

[ecy5maa]

Hi,

I understand that you cannot apply KVL to voltage sources connected in parallel, unless both voltage sources are the same, as this violates KVL.

However, I want to know why? Just a simple 2-3 line explanation will suffice.

Regards

 

[MATLABdude]

From a KVL point of view, if you summed up the voltages around the loop, they wouldn't add up to zero.

From a practical point of view, you'll have one battery charging the other (assuming the polarities were correct, and the voltages were appropriate), or, if they were severely mismatched, one (if not both) would probably blow up. That or the wire connecting them would get really, really hot (acting as a low resistance resistor).

EDIT: I should clarify that when you go around the loop and take account of all the voltages, you have to set that to zero, which leads to mathematical inconsistencies as sophiecentaur mentions below. For instance, write out the KVL equation for a 2V supply in parallel with a 3V supply, such that like terminals are connected together (+ with +, - with -).

 

[sophiecentaur]

Hi,

I understand that you cannot apply KVL to voltage sources connected in parallel, unless both voltage sources are the same, as this violates KVL.

However, I want to know why? Just a simple 2-3 line explanation will suffice.

Regards

A voltage source is a fixed value, whatever the load. Modelling the effect of connecting two in parallel would be like trying to do maths but saying 3=2.