Triad RF Systems
RF Electronics Symbols, Stencils for Office, Visio by RF Cafe
 

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

AirplanesAndRockets.com

Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
Innovative Power Products Couplers

AA battery as Thevenin not Norton - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. If the folks at phpBB would release a version with integrated sign-in from the major social media platforms, I would resurrect the RF Cafe Forums, but until then it is probably not worth the effort. Regardless, there are still lots of great posts in the archive that ware worth looking at.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

Uncle Ezra
Post subject: AA battery as Thevenin not Norton
Unread postPosted: Tue Dec 28, 2004 8:33 am

Why AA battery represented as Thevenin instead of Norton?

Thanks


Top


Guest
Post subject:
Unread postPosted: Wed Jan 05, 2005 7:55 am

This is obvious: when you represent a battery as an ideal voltage source with an internal resistor in series you get what you actually have: when you measure its terminal voltage with a very high resistance instrument you (almost) get the voltage of the (ideal) source, when you short is, you get the short circuit current. when you repeat these measurements some time later you get the same results.

However, when you represent it as an ideal current source with an internal resistor in parallel you will find that at first your measurements agree with the voltage source model, but after a finite time they don't: the battery has run out.

Some figures: an AA battery has a terminal voltage of 1.5 V, a short circuit current of about 10 A and a capacity of about 1 Ah.

This means it has an internal resistance of 1.5/10=0.15 ohm.

A voltage measurement on the Thevenin equivalent with a standard 10Mohm DVM will yield 1,49999978 V. Even on a six-digit instrument this will round to 1.50000 V.
This measurement can be repeated after several years, and will give the same results, provided that the battery is kept at a constant temperature.


If the battery is considered to be its Norton equivalent, the 10A source will feed its current through the 0.15 ohm resistor, giving -indeed- a terminal voltage of 1.50000 V. However, after 1/10 hour or 6 minutes, the battery will have run out, so the experiment can not be repeated.

You can see, never believe your teachers when they say that Thevenin and Norton are equivalent!


Top


maxwell
Post subject:
Unread postPosted: Wed Jan 05, 2005 9:13 am
Offline
Captain
User avatar

Joined: Mon Sep 01, 2003 6:59 pm
Posts: 13
Location: Boston
:smt038 Your entire post is a great answer, I wish all responses were this complete! Thanks for putting the effort into it.


Anonymous wrote:
You can see, never believe your teachers when they say that Thevenin and Norton are equivalent!

While I realize this is a tongue-in-cheek remark, in fact it is true that Norton and Thevenin are equivalent if you are mindful of the ideal current/voltage supplies used in the theoretical models, whereas the battery source is not ideal and therefore favors one model over the other.

Keep up the great work!


Top
Profile

hugo
Post subject:
Unread postPosted: Mon Jan 10, 2005 8:33 am
Offline
Lieutenant

Joined: Mon Jan 10, 2005 7:13 am
Posts: 1
Location: the Netherlands
This is quite a compliment to get from dr. Maxwell himself, or is his deamon speaking? However, after figuring out how to sign this post, I have to comment. This is not tongue-in-cheek at all!

Proof:

Suppose you have an ideal voltage source of 1 V and an ideal current source of 1 A (naturally the latter one is carefully shorted). Let's say that you got them from an alien or that you are only conducting a thought-experiment, but the sources are realy IDEAL, including the fact that the sources are inexhaustable.

Now, to teach your pupils the Norton-Thevenin equivalency theorem, you mount the voltage source in a black box, connect it to two external terminals and insert a 1 ohm resistor in series with the voltage source. You do the same thing with te current source, but there the 1 ohm resistor is shorting the terminals.

Now, you demnstrate before your class that:
- the open circuit voltage is equal
- the short circuit current is the same
- the voltage and current with any load, even an artifially made negative resistance is equal

proving that Norton and Thevenin are equivalent.

However, now a smart student comes forward and proposes the following experiment: put both black boxes (wit open terminals) in two equal reservoirs filled with an equal amount of deionised water. Both reservoirs are prety good thermal insulators and equipped with a thermometer.

When we observe temperature over time in both devices, we will see that one of them is rising, while the other one remains at room temperature.

It can easily be seen that the device with the rising temperature contaisn the current source, while this black box is dissipating 1W of power. Hence the other one is te voltage source.

QED, Norton and Thevenin are NOT equivalent, you can -evidently- device a thought-experiment that distinguishes them. :wink:



Posted  11/12/2012
TotalTemp Technologies (Thermal Platforms) - RF Cafe
PCB Directory (Assembly)
LOTUS Communications Systems Modular RF Component Building Blocks - RF Cafe
 

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free