Harold Hall
Metalworking
Workshop Data
Fortunately, the reversal of the induced voltage permits a diode to be added across the coil that will only conduct on switch off, Sk 20/B. This current will hold up the field strength reducing the rate of change and the magnitude of the back emf, Sk 21.
Inductors and capacitors compared
Whilst the calculations, and resulting waveforms, relating to the "time constant" of both inductors and capacitors are similar, there are some important differences. Most important is that a capacitor opposes changes in voltage, but an inductor, changes in current.
Click here for a clearer image of SK 21
Another important difference occurs on switch off as a capacitor can retain its charge on switch off whilst an inductor cannot causing the problems as mentioned above.
In the wider world of electrical /
electronic equipment capacitors are very much more used for the characteristics they possess than do inductors. As a result, inductance can largely be ignored in the case of the equipment of interest to viewers, even though it will be in existence (in the background) for many of the components used, such as relay coils, transformers, and electric motors.
Other Pages
See also my pages on Basic Electrical Theory for AC circuits, Basic electronics and electric motors
Further viewing/reading
The following are just a few of a vast number of web sites that may also be of help. A search on Google will list many more.
Websites
www.tpub.com/neets/book2/index.htm
Should any viewer find a helpful website do let me know and I will add it to the list.
Books
Also, at the end of my article in the magazine, David Fenner (editor of the Model Engineers Workshop magazine) mentioned a few books that he, as a largely mechanical engineer, had found useful. These were.
Electrical Technology by E Hughes published by Longmans
Practical Electronics by Barry Woodland published by McGraw-
Practical Digital Electronics by Mike Tooley published by PC Publishing
Electric Motors by Jim Cox published by Special Interest Model Books
Electric Motors In The Home Workshop by Jim Cox published by Special Interest Model Books
