# RC Time Constants

Discussion in 'Feedback and Suggestions' started by Wendy, Aug 31, 2009.

1. ### Wendy Thread Starter Moderator

Mar 24, 2008
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I'm working on some projects that may or may not wind up in the book. I looked for an old concept I was taught as a tech, the RC time constant, and can not find it anywhere in the AAC book. Am I missing it, or is this an oversight?

According to "Electronic Communication", 3rd Edition, by Robert L. Shrader, Tc = RC

Tc is in seconds
R is in ohms

1 Tc is 63% of a charge, or change in voltage on a cap from charging/discharging. 5 Tc is a full charge (basically an arbitrary figure, but a good one).

There is a similar concept for inductors, the LR time constant, which is expressed by the equation of Tc = L/R

The difference is the inductor deals with current, while the capacitor deals with voltage.

Both of these equations are simplifications of the calculas equation that actually determines this. I'm working on determining an inductance using the LR time constant, which led me down this path.

If it is not in the AAC book I really feel it should be added.

Last edited: Aug 31, 2009
2. ### Wendy Thread Starter Moderator

Mar 24, 2008
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I'm going to bring this up again, because I feel it is lacking. If it is in the book and I missed it I would appriciate it being pointed out, but I can't find it. A reader would have no clue why 5 RC time constants is considered a full charge (this also applies to inductors in the form of LC time constants), this is basic information that need to be there.

I would not mind adding a blub to Series resistor-inductor circuits and Series resistor-capacitor circuits, but I need some feedback (and someone telling me they can't find it either).

********************************

Never mind, found it.

RC AND L/R TIME CONSTANTS

It is in Volume 1, DC circuits, in Chapters 13 and 14, I was looking in Volume 3.

Last edited: Oct 22, 2009
3. ### studiot AAC Fanatic!

Nov 9, 2007
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This is why I think the 'book' needs a proper index/cross referencing system.

4. ### Wendy Thread Starter Moderator

Mar 24, 2008
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The PDF version has it. Since the HTML version doesn't truely have page numbers it almost has to be with links. Another possibility is a search function, which seems more reasonable on the face of it. You could take the existing PDF Index and use it for a keyword search.