## DC Circuits Week 7

#### This material given in advance for you to prepare for the following weeks lesson. We have less time in the classroom for this learning, so it is important that you do the study at home. When you come to class you should know this material in advance. I have supplied a powerpoint to guide you through what you need to learn. There are powerpoint slides on the topics and some reading as well. Keep checking back as I am updating this daily.

LINKS TO POWERPOINTS etc |
LOCKED – PASSWORD NEEDED |

Wheatstone Bridge by Greg Moore | Wheatstone Bridge by Greg Moore |

Capacitors Participatory ppt, TAFE | Topic 15 Capacitors PPT 1 |

Capacitors series parallel Participatory ppt, TAFE | Topic 16 Capacitors PPT 2 |

More powerpoints coming soon, stay tuned! | |

Cook text section on caps | Text Material Capacitors for time constants |

There is so so much stuff to know about capacitors.

But basically if you can know about charge on a capacitor, and charging current, discharging current…. charging voltage and discharging voltage and some safety considerations like voltage ratings, and some WHS awareness – because capacitors can be lethal, .. well that is maybe enough for our study. So, it’s some maths, some type differences, some safety, some usage in circuits, and we are home and hosed.

Be sure to watch the video links I have added in the menu area.

here is a video of rapidly charging a 1F capacitor, which discharges very slowly into a LED. Charging a 1F capacitor will put a lot of pressure on a conventional power supply and may cause it to blow a fuse. There should be some resistance in series with the capacitor to limit the charging current at surge.

## Study at TAFE – get the very best training.

# Here is the video lab:

##### In the study of capacitors as part of DC circuits we need to know how to calculate the total value of charge and voltage across series and parallel connected capacitors. Additionally we need to learn about charging and discharging capacitors and making pre-determined time delays based on the value of R and C in a simple circuit. This video is about the time delays involved with RC circuits. 8 minutes.

##### Next is an interesting (if not too formal) lab. Roly shows how to layout the lab on a breadboard (it’s very neat! maybe even obsessively neat) and measure the duration of one time constant on a digital oscilloscope. No audio… pity, this guy looks and sounds like Sean Connery. Roly is a PhD in Electrical Engineering and teaches at the University of British Columbia, Vancouver. Compared to his method, there is nothing wrong with going top to bottom of the FULL charging cycle and then applying 5 time constants to the duration and dividing by 5. BUT if you do not have the entire 5 time constant rise of the circuit, then the method here is the best. Note the use of a square wave voltage applied across the capacitor, to charge and discharge it, and the symmetry gained by using a 50% on off cycle in the square wave.

#### Really nicely built circuit above compared to the circuit below. Must get the colours right in the video next time too! Gotta get that yellow out!

Then on the other hand, my video took 2 hours to design and produce. I think this other video needed maybe 25 hours. 🙂

#### Material on capacitor time constants concludes.

Ye olde stuffy beneathy … from previous teachings etc.

#### Review of series parallel and introduction to capacitors and charge / discharge