Thank you for visiting RF Cafe! Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums RF Cafe Homepage Thank you for visiting RF Cafe!

AA Battery as Thevenin Not Norton - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

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?



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!


Post subject:
Unread postPosted: Wed Jan 05, 2005 9:13 am
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!


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

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!


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

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Kirt Blattenberger,

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 Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

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:

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !