Test method for sealed lead acid batteries?
What is the most reliable test method for sealed lead acid batteries?
This has been something I have been working on for a number of years and now it is a matter that needs to be resolved for inclusion in Australian Standard AS1851.
In most cases, we use sealed lead acid batteries sometimes known as gel cell batteries in fire panels and emergency warning systems.
These systems usually combine two 12v batteries wired in series (24v) and range in size from 7Ah through to 200Ah.
The problem is that we are currently unable to determine if a battery will pass or fail under full load conditions.
I have trialled the following systems with inconsistent results;
- NoClimb - Cellchecker Battery Tester
Rather than simply displaying a voltage reading, Cellchecker? determines a battery?s remaining power capacity by measuring its ability to maintain voltage levels while under load. The tester then makes an assessment based on these readings and displays the remaining percentage capacity of the battery. Pulse load testers verify that a battery can deliver power by actually making it deliver power.
- ACT - GOLD-IBT Intelligent Battery Tester
The GOLD-IBT Intelligent Battery Tester solves this problem by measuring temperature, voltage AND capacity in under 6 seconds. It achieves this by performing a conventional 20 hour battery discharge in seconds using a patented pulsed frequency load test which accurately measures the available Ampere-hour (Ah) capacity based on the the battery?s temperature and condition of charge.
According the Cellchecker web site there are problems with each method of determining a battery's state of charge and condition;
Alternatives to Pulse Load testing
Depending on the type/chemistry of the battery, there are several different testing methods on the market. These methods include simple voltage measurement, coulomb counting, impedance / conductance measurement, and in some cases electrolyte analysis. Acceptable methods vary by battery type or chemistry.
For example, one of the characteristics of the lithium (LiMnO2) and NiMH chemistries is that they have a relatively flat discharge curve. This means that the battery's terminal voltage is nearly the same at 90% capacity or 40% capacity, compared to other chemistries such as alkaline or lead-acid whose voltage decreases steadily with discharge. Simply measuring the battery's voltage or even voltage under a small load, like many conventional battery testers do, is not, therefore, a reliable method to test these types of chemistries.
The alternative of measuring and recording the amount of current discharge (coulomb counting), has its drawbacks in primary cells because it assumes that the battery begins with full capacity ? an assumption that ignores age and other factors as well as assuming that the battery will be able to actually deliver its capacity at the necessary rate.
Impedance and conductance measurement methods in lead-acid type batteries also assume that the battery will be able to deliver its measured capacity.
Calling for your help?
As you can tell, I have been thinking about this for some time and now I am asking for your help for an answer... If you have a suggestion for a battery test method, system or a link to a great web site, then please add your comments below..
I look forward to your feedback..