World Library  
Flag as Inappropriate
Email this Article

Internal resistance

Article Id: WHEBN0000861162
Reproduction Date:

Title: Internal resistance  
Author: World Heritage Encyclopedia
Language: English
Subject: Supercapacitor, Electrical resistance and conductance
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Internal resistance

A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This resistance is termed the internal resistance of the source. When the power source delivers current, the measured voltage output is lower than the no-load voltage; the difference is the voltage drop (the product of current and resistance) caused by the internal resistance. The concept of internal resistance applies to all kinds of electrical sources and is useful for analyzing many types of electrical circuits.

Batteries

Batteries can be approximately modeled as a voltage source in series with a resistance. The internal resistance of a battery is dependent on the specific battery's size, chemical properties, age, temperature and the discharge current. It has an electronic component due to the resistivity of the battery's component materials and an ionic component due to electrochemical factors such as electrolyte conductivity, ion mobility, and electrode surface area. Measurement of the internal resistance of a battery is a guide to its condition, but may not apply at other than the test conditions. Measurement with an alternating current, typically at a frequency of 1kHz, may underestimate the resistance, as the frequency may be too high to take into account the slower electrochemical processes. Internal resistance depends upon temperature; for example, a fresh Energizer E91 AA alkaline primary battery drops from about 0.9 ohms at -40 °C, where the low temperature reduces ion mobility, to about 0.15 ohms at room temperature and about 0.1 ohms at 40 °C.[1]

The internal resistance of a battery can be calculated from its open circuit voltage, voltage on-load, and the load resistance:

R_{\text{int}} = ({\frac{ V_{\text{NL}} } { V_{\text{FL}} }  - 1 } ) { R_{\text{L}} }   

Many equivalent series resistance (ESR) meters, essentially AC milliohmmeters normally used to measure the ESR of capacitors, can be used to estimate battery internal resistance, particularly to check the state of discharge of a battery rather than obtain an accurate dc value.[2] Some chargers for rechargeable batteries indicate the ESR.

In use the voltage across the terminals of a disposable battery driving a load decreases until it drops too low to be useful; this is largely due to an increase in internal resistance rather than a drop in the voltage of the equivalent source.

With rechargeable lithium polymer batteries the internal resistance is largely independent of the state of charge, but increases as the battery ages, thus is a good indicator of expected life.[3][4]

See also

References

  1. ^ "Battery Internal Resistance". Energizer Technical Bulletin.  
  2. ^ Testing batteries with ESR meter
  3. ^ Understanding RC LiPo Batteries
  4. ^ ESR Meter For 2 – 6 Cell Lipo Packs - instructions
  • Student Reference Manual for Electronic Instrumentation Laboratories (2nd Edition) - Stanley Wolf & Richard F.M. Smith
  • Fundamentals of Electric Circuits (4th Edition) - Charles Alexander & Matthew Sadiku

External links

  • Interconnection of two audio units - Output impedance and input impedance
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.