Lead Acid Batteries 

By on

Lead acid batteries are cost effect and reliable, making them suitable for many applications.This note examines topics of interest associated with the use of these batteries.

Discharge & Peukert's Law

The capacity of lead acid batteries decrease as the charging rate is increased. The action of a battery under these conditions is described by Peukert's law (first proposed by German scientist Peukert in 1897):

  t= C p I k

Where:
t = time to discharge the battery, in S
Cp = battery capacity at 1 A.h discharge rate

I = the actual discharge current, in h
k = Peukert constant (dependant on battery, typically 1.1 to .13)

 

Typically batteries are rated at a discharge time, T (in hours) and rated capacity C.  Perkert's law can then be expressed as:

  t=H ( C IH ) k

Peukert's law is good for reasonably constant rates of discharge.  For variable and non-linear rates, it starts to become inaccurate.  Replacing I with the average current during the discharge will give a better result, but it is still limited.   In this instance several methods can be used to improve accurately, including:

  • Rakhmatov and Vrudhula Model - looks at the actual diffusion processes within the battery to derive a more accurate analysis
  • Kinetic Battery Model - uses the chemical kinetics process as a basis for developing a discharge model
  • Stochastic Models - analysis the battery as a stochastic process
Typical accuracy using Peukert's law is in the order of 10% error.   Rakhmatov and Vrudhula models improve on this having errors around 5%, while Kinetic and Stochastic models perform even better with errors as low as 1 to 2%[1].

 

Effect of Temperature


Effect of temperature on battery life
 

Lead acid batteries are cost effective and reliable, making them suitable for many applications. One serious drawback compared to some other batteries (NiCad for example), is that lead acid batteries are affected by temperature. Lead acid batteries should only be used where they are installed in conditioned environments not subject to excessive temperatures.

Typically the rating for lead acid batteries is based on an ambient temperature of 25oC. For every 8oC above ambient during use, the life of the battery will be reduced by 50%. Ideally batteries should be operated at 25oC or less.

In addition to operation, storage of batteries waiting for use is also affected by temperature. If lead acid batteries are stored at elevated temperatures (particularly in a discharged condition), they will effectively become useless. If storing batteries, they should be in charged and stored at 25oC or less. Batteries will self discharge over time and need to be recharged periodically.

References

  • [1]  Battery Modeling, M.R. Jongerden and B.R. Haverkort - doc.utwente.nl/64556/1/BatteryRep4.pdf, accessed November 2012.


Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



Periodic Electrical Installation Inspection – What to Inspect?

This is the second post in a series of two on periodic electrical inspections. In the first post, I discussed how often inspections should be carried out...

Three Phase Current - Simple Calculation

The calculation of current in a three phase system has been brought up on our site feedback and is a discussion I seem to get involved in every now and...

1,000 kV UHV First for China

At the beginning of the year China put the world's first 1,000 kV UHV transmission system into operation. Transmitting power at over a million volts is...

Introduction to Traction Substations

Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. Traction substations...

UPS Sizing - Rules of Thumb

It wasn't so long ago I was telling someone that I don't use rules of thumb as most things are easily calculated anyhow.   As it turns out I last week...

Lightning Protection and Earth Electrode Resistance

Most installations involve some form of lightning protection system which is connected to an earth electrode.  The function of the earth electrode is to...

Resistors

Resistors are electronic components that oppose the flow of current.  Manufactured in various types and ranges they have a wide application to electronics...

How to refer fault levels across a transformer

Over the past year or so I've been involved in on going discussions related to referring fault levels from the secondary of a transformer to the primary...

Famous Scientists

Here’s list of some famous scientists. Deliberately short, with the aim to provide a quick memory jog or overview. If your looking for more detailed information...

Capacitors - Energy Storage Application

Capacitors have numerous applications in electrical and electronic applications.  This note examines the use of capacitors to store electrical energy....

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note