Basic AC Mains voltage simulation

Schematic Simulation (Ngspice)
1

I am having trouble understanding how to model AC mains voltage. Or rather I am modelling it how I see as correctly, and yet the transient analysis produces something incomprehensible to me.

I have modelled a VSIN source, with a GND with the following parameters

dc=0 ampl=240 f=50hz ac=1

Across this I have put a 1m Resistor as a load.

I have created a label called “in”

I run my transient analysis with a timestep of 20ms and a final time of 1s

I expect to see a sinusoidal trace in the transient, because, well frankly it’s a sinusoid!

What I get is a mostly flat line at around 240v with a spike to 0 at the start and end of the trace.

How on earth is it possible with such a simple circuit to not get a sinusoid?

2

Did you intend to put a 1e-3 resistor

2 Likes
3

1M resistor, pardon me.

4

20ms steps are far too large if you wish to see a 50Hz signal: 20ms is one full period.
Try steps of 500us or less and there will be a shape you will recognise.

But don’t forget that a time of 1s horizontally means you will see fifty full cycles. Perhaps you could also reduce this (unless you have a rather wide monitor) to maybe 0.2s or less.

5

you put a timestep of 20ms… the period of 50Hz is 20ms, so yes, you will only simulate the PEAKS, ie “dc”

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1 Like
6

Thank you kindly all. I have remedied my (rather basic) mistake.