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



What does N+1 mean?

The term 'N+1' relates to redundancy and simply means that if you required 'N' items of equipment for something to work, you would have one additional...

LED Replacement Light Bulb

The inventor of the first visible light-emitting diode makes history again this year as it begins to show customers a 40-watt replacement GE Energy Smart...

E-Ink

Before the technical, some general information. E-ink display are found in a lot of e-readers, some mobile phones and similar devices and the intent is...

Paths of Flight

GE have put together a time-lapse video shown flight take-off and landings at some airports. An interesting view:

What is an Open Delta Transformer

In three phase systems, the use of transformers with three windings (or legs) per side is common.  These three windings are often connected in delta or...

UPS - Uninterruptible Power Supply

A UPS is an uninterruptible power supply.  It is a device which maintains a continuous supply of electrical power, even in the event of failure of the...

Electromagnetic Compatibility (EMC)

Electromagnetic compatibility (EMC) is the study of coordinating electromagnetic fields give off equipment, with the withstand (compatibility) of other...

Why is electricity so hard to understand?

It's been a busy few months on different projects or busy couple of decades depending on how I look at it. I can say that on the odd (frequent) occasion...

Operational Amplifier

The fundamental component of any analogue computer is the operational amplifier, or op amp. An operational amplifier (often called an op-amp,) is a high...

Thomas Edison

American inventor Thomas Alva Edison was born in Milan, Ohio on February 11, 1847. He was the youngest of seven children and received little formal schooling...

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