See what happens inside an electrical circuit

One part per line: NAME node1 node2 value.   Node 0 (or gnd) is ground. Lines starting with * are comments.
Values accept suffixes: f p n u m k meg g t   (10m = 0.01, 4.7u = 0.0000047, 2meg = 2,000,000)

R1 a b 10                Resistor, ohms
L1 a b 5m                Inductor, henries
C1 a b 100u              Capacitor, farads
K1 L1 L2 0.98            Couples two inductors (a transformer). Coupling 0 to 0.9999
V1 a b DC 12             Voltage source. Also: SIN amp freq [phase_deg] [offset]
                         STEP value start_time      PULSE v1 v2 delay rise fall width period
I1 a b DC 2              Current source (current flows a to b through the source)
V1 g 0 SYNC e=11k s=25meg [f=60 h=2 p0=10meg delta=5 d=2 droop=0.05 tg=0.5 pmax=1 hold=50m
                          pmin=-1 wh=50meg soc0=0.6 ramp=1]
                         Generator with inertia: voltage e (peak) at an angle that moves with a swing equation
                         (h = inertia in seconds, s = rating in watts, p0 = scheduled power, droop 0 = isochronous).
                         Models three identical phases, so power is 3 x the one-phase value.
                         With pmin=-1 and wh= (energy in watt-hours) it acts as a grid-forming battery that can charge and
                         discharge. S(V1) plots its state of charge in percent; it cannot discharge when empty or charge when full.
I2 0 bus FOLLOW V1 100 [t0=4 ramp=1.5 n=8 stag=0.5]
                         Current source of peak 100 A that copies the angle of generator V1 (an ideal PLL).
                         Optional: n identical units start one after another from time t0, every stag seconds, each
                         ramping up over ramp seconds (a wind farm starting). The peak current is per unit.
SW1 a b 10m [20m]        Switch: closes at 10 ms, optional opening time. Or: SW1 a b PWM 20k 0.5
D1 anode cathode         Ideal diode
.tran 10u 20m            Time step and stop time   (required)
.probe V(a) V(a,b) I(L1) What to plot: node voltage, voltage between two nodes, part current
                         F(V1) = generator frequency in Hz, D(V1) = generator angle in degrees, S(V1) = battery charge in %

Currents are positive from the first node to the second node of the part.
Opening a switch while current flows through an inductor makes a huge voltage spike, just like in real life.
Switching converters: when an inductor's current first drops to zero (for example during start-up), the voltage at a
floating switch/diode node can show brief numerical ringing. It does not affect the other results.