Episode 93 — Capacitors

capacitorElectrical engineer James Lewis stops by to share his insights on the surprisingly complex world of capacitors.

  • Carmen introduces the show as covering “passives.” This refers to passive electrical devices that have no control over voltage, current, or signal gain.
  • Our guest for this episode is electrical engineer James Lewis, a Marketing Director for capacitor manufacturing firm KEMET.
  • Jeff notes a series of articles on the Dangerous Prototypes website titled “Passives Aren’t Really So Passive.”
  • Brian references using “NPO” capacitors, which refers to a highly stable form of ceramic capacitor.
  • James got interested in electronics during high school, when he discovered he could overclock his TI-85 calculator by swapping out a capacitor.
  • Apparently Carmen spent too many hours playing Block Dude on his calculator during his high school days.
  • Our guest became a field application engineer (FAE) upon graduating from college.
  • According to James, a deep knowledge of materials and chemical processes is crucial for developing and manufacturing capacitors.
  • There are five typical uses for capacitors:
    1. Decoupling: Removing noise (or alternating current elements) from a fixed voltage signal signal.
    2. Filtering: Removing unwanted signal frequencies.
    3. Wave Shaping: Using a capacitor’s charging and discharging characteristics to create desired waveforms.
    4. Coupling: Allowing desired frequency elements to pass from one circuit stage to the next.
    5. Oscillation: Creating a sinusoidal waveform of a desired frequency.
  • For a long time, it was widely claimed that everyone should drink 8 glasses of water a day. Now, that viewpoint is much less prevalent.
  • Carmen, Jeff and Brian have distinctly different viewpoints about how a capacitor works.
  • A range of materials and construction methods can be used to create capacitors with differing performance characteristics:
    1. Ceramic capacitors are thermally stable and provide precise capacitive values.
    2. Electrolytic capacitors (either aluminum or tantalum) are good for storing a large amount of charge.
    3. Film capacitors can handle voltages in excess of 500 volts.
  • Although ideal capacitors theoretically exhibit no resistance or inductance, real-world capacitors are subject to equivalent series resistance (ESR) and equivalent series inductance (ESL).
  • KEMET has a tool called K-Sim which allows designers to view how capacitor parameters vary with frequency, voltage, and temperature.
  • When he was working as an FAE, James encountered problems with counterfeit capacitors at least once a month.
  • Under the heading of “Why did they do that?”, the electronics industry marks the negative lead (cathode) of aluminum electrolytic capacitors, and the positive lead (anode) of tantalum electrolytic capacitors.
  • Supercapacitors bridge the gap between capacitors and batteries.
  • While James is sure graphene will lead to better capacitors, he still waiting for its breakthrough application.
  • EEStor is a company claiming significant advances in capacitor charge density and operating voltages.
  • James mentions the KEMET Engineering Center and KEMET Institute of Technology (KIT) as resources for engineers wanting to learn more about capacitors.
  • A more technically in-depth interview with James about capacitor performance can be found on Episode 25 of the Spark Gap podcast.
  • James publishes instructional videos about electronics on his AddOhms YouTube channel.
  • Listeners can delve into our guest’s writings on his Bald Engineer blog.
  • James can be found on Twitter as @baldengineer.

Thanks to Kiran Foster for the photo titled “capacitor.” Podcast theme music by Paul Stevenson.