## Wednesday, June 8, 2011

### Tutorial: Electrical impedance made easy - Part 1

This is the first video of a short series in which I discuss the basics of electrical impedance from a practical standpoint.

In this video, I show how a simple LED power supply circuit can be made more efficient by replacing a resistor with a capacitor. I describe the difference between resistance, reactance, and impedance.

1. Impedance always was a hazy concept for me, thanks for producing this!

2. This is good, never really had a good feel for impedance. Can't wait for the power factor.

3. So clearly explained! Awesome!Love your work & thanks so much for all your videos and explanations!

4. Enjoy your blogs! Just a clarification, should not the 1 k resistor need to be higher wattage than the 5 k? P=VI or P=V2/R, the bigger the resistor the less the power dissipation? Thanks

5. Abizar, I had this same problem understanding resistors. After all, if you connect a 10-ohm resistor directly to your power supply, it will get much hotter than a 10k-ohm resistor. However, this assumes the voltage across the resistor is constant (coming directly from a power supply in this case). If the resistor is part of a larger circuit, and the voltage across it is not fixed, using larger values of resistance will generally cause a larger voltage drop for a given circuit current, and hence more power dissipation.

Think of electrical extension cords. A thick, low-resistance cord will generate less heat than a thinner, higher-resistance cord for the same length, powering the same device.

For applications, where the circuit current is known, use (I^2)(R) to find power dissipation in a resistor.

I hope this helps.

6. Another great tut'.
And you have a really clear speaking so even a french guy like me can understand it.
Thank you.

7. Great tutorial! Keep up the good work!

8. I really like your tutorials and anxiously wait for more. Thanks!

9. I originally saw your site on hackaday.com, always looking to learn new stuff. absolutely great stuff man keep it up

10. well done, ben. i have one correction though: the current direction will flip 120 times a second, twice for every cycle

11. Keep these coming Ben! Gold!

12. Thank you! This so helpful to newbies like myself. Please keep these tutorials coming. You might also consider posting these on metacafe.com after enough views you'll start getting paid for your videos.

I have a question. I tried to use a 555 to trigger a 12 volt auto siren. The timer works fine with an led, but gets stuck on when I switch to the siren. Should I be using a resistor to limit how much power the siren can draw?

13. SlackFarmer, thanks. Your siren may require more current than the 555 chip can supply. Connecting an LED through a current-limiting resistor to a 555 works because the LED only draws 20mA or so. A siren might draw a few hundred mA (depending on its size). Your best bet is to use a small transistor between the 555 and siren to allow the small current from the 555 to control the high current needed by the siren. Search my blog or youtube channel for a tutorial on transistors. Good luck!

14. Thanks for this - I'm a software engineer by day and learning to control step motors and the like by night. Your tutorials are a great help!

15. Awesome work. Thank you!!

16. I really enjoyed the review these two videos provided, and learned a lot from the video where you demonstrated the usage of transistors.
I'm going into my second year of electrical engineering and was wondering if you would do something similar for three phase power? They're going to try to teach me it in September, and it would be great to have a well put together summary.

17. Great stuff! can't wait for the next one!

18. It took me over 30 years, but I think I understand impedance now.

19. Very helpful video I happened upon on google while trying to learn about impedance for a quiz (and no book yet!). Thanks very much!

20. wow! thank you very much! :)

21. Why, oh why, couldn't others explain this concept as lucidly as you did, Ben? Thank you so much for clearing this up. I'm in electrical engineering and while I understand the math, the practicality of it all was eluding me. Not anymore!