RAGE BRIDGE

RAGEBRIDGE is the name of a motor controller.  Calm down now. A large arc appears across the connector, caused by capacitive load discharging (I assume).

So we ran over capacitors in class.  Not literally. We might have literally blown an electrolytic though. Woo!
Capacitors aren't so crazy.  Recall from physics:
q = Cv
and
C = e_0*A/d.
This describes how to treat a capacitor in a nutshell.
There was a long treatment of what capacitors are.  I'm going to instead describe what electrolytics are.  Electrolytics are made of salt in solvent with aluminum electrodes.  They're bigger than most capacitors, but they're fairly cheap, and have a wide range of capacitances up into the micro Farads.

One has to be careful about which lead is which, electrolytics are limited in their ability to be voltage biased in one direction.

There are some others. They're all neat. My fingers lament my not wanting to type about them.

Capacitors generally block dc, pass ac, shift phase to the right, and can be used to start motors or suppress noise. The useful thing to know:
i = C*dv/dt  &  v = 1/C * integral(i)dt from t_0 to t.
and the energy stored, w, which is represented as the integral from -inf to t:
w = C*integral(p=v*dv) = 1/2*C*v^2 from -inf to t.
If we note that v = q/C, then
w = q^2/(2C)

Beyond math, the important properties of a capacitor are:
A. The voltage across a cap cannot change instantaneously
B. The current across a cap at DC approaches zero
C. Ideal caps don't dissipate energy
D. non ideal capacitors may leak a little current.
We did an in-class example of how capacitors behave.  Calculations:


Capacitor Voltage Lab

1. sketched cap voltage/current for all inputs


So we applied a sinusoidal frequency at 1 and 2kHz and 2V to a series RC, and then did the same with a triangular input voltage at 100Hz, 4V. See below:

2,3,4 Oscilloscope windows


We used the software's math toolbox on the scope to view both the current and the voltage.  We know the current because we can calculate it as a function of the measured Voltage, and the known resistance.



2kHz sinusoidal input













1kHz sinusoidal input











Triangular 100 Hz input

Circuit with an inductor                                          Circuit with a capacitor

We repeated the lab for inductors:


In this lab, we demonstrated the capacitor current at various AC supplies, and how reactive components shift the voltage signal out of phase. Voltage across inductors leads the resistive voltage, and capacitive voltage lags resistive voltage.