I am trying to simulate a series parallel battery design.
When I try to simulate, I am getting this error:
Voltage source loop found: V9, V1, V2, V10.
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Please help me out.
It's quite simple; don't put voltage sources directly in parallel. If you want to do this less directly, use a small value series resistance for each battery. 1 μΩ would do (even though it's far below any battery series resistance that I'm aware of). This would probably suffice: -
When you ask a simulator to solve a circuit, it has to be able to find everything. As the voltage sources you have used are zero impedance, a loop of voltage sources could have an undefined current circulating round them, which it's mathematically not possible to evaluate.
This simulator is rather more helpful than many in its error message. It tells you there is a voltage source loop comprising V1, V2, V9 and V10. Most simulators will say something like 'non-invertible matrix', and leave it to you to figure out what the problem is and which components are causing it.
Putting a finite resistance in series with each parallel branch will allow the simulator to construct the extra equations it needs to resolve the individual cell currents. As Andy says, 1 μΩ will do, though you could use a larger, more realistic, value for your particular voltage sources.
Another good way that simulators confuse us is with a 'floating node', for instance a junction between two capacitors with no DC path to ground. The voltage on that node cannot be found, which is a dual of the problem you are seeing. The cure for that is a large resistor to ground, 100 MΩ will often do.