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Publication Title | Diagnosing Battery Problems

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Batteries

Diagnosing

Battery

Problems Richard Perez

you don't put it in, then you can't take it out. Most folks who think that their battery has lost capacity really just need to give it a full recharging.

The Diagnostic Procedure

This procedure is simply recharging and discharging the battery (or better yet, each cell individually) and making measurements of its performance. Just fill the battery or cell until you are really sure it is full and then measure how much you can get out of it.

There is a big difference between running this diagnostic procedure on a series-connected string of cells (a battery) and running the procedure on a single cell. The capacity of a series string of cells (a battery) is limited to the capacity of the weakest cell. Consider this example: A 12 Volt lead-acid battery is composed of six series- connected 100 Ampere-hour cells. One of the six cells has lost capacity and now holds 50 Ampere-hours. The entire battery will have a capacity of 50 Ampere-hours, even though five of the six cells still contain 100 Ampere-hours.

If this procedure is applied to a battery (a series connected string of cells), then it will yield the capacity of the weakest cell in the string. If the procedure is applied to each cell, then you will know exactly which cells are good and which are not.

Before beginning this procedure, give each cell in the battery a name or number. Get a clipboard and get ready to record all the measurements you will make. If you have a battery Ampere-hour meter (like the Cruising Equip. models), then you already have an instrument that will be of great aid in diagnosing lost capacity. You will need an accurate voltmeter like the Fluke, Beckman, or even a Radio Shack digital multimeter (DMM). If you are making your own power and operating a battery, you should have a DMM. If you don't have one, then now is the time to buy one because you are going to need it.

First Really Fill Up the Bucket

Recharge the battery or cell. Since most perceived capacity loss is actually chronic undercharging, first examine your charging system. Number one on the hit parade is any regulator or charge controller. If the voltage cutoff or regulation point of the regulator is set too low, then the battery is not being fully recharged. Check your regulators. Set the regulator for 1.6 VDC for each series connected cell in an alkaline system. This means 16 VDC for a ten series cell nicad or nickel-iron battery. In lead-acid systems, set the regulator at 2.66 VDC per series connected lead-acid cell. This means 16 VDC for six lead-acid cells in series. This information applies to

If a battery is like a bucket, then a sick battery is like a bucket with holes in it. Batteries and buckets share some

common characteristics. When they are full they will hold no more. When they are empty, they will deliver no more. Both batteries and buckets can leak. In the case of a bucket, we get a puddle on the floor. In the case of a battery, we get a diminished capacity to store power. Here's how to find out if your battery stores as much energy as it used to.

Different Batteries, Similar Diagnostics

This article deals with diagnosing capacity loss in both acid and alkaline electrochemical cells. High-antimony, deep cycle lead-acid cells and pocket-plate nickel cadmium cells have radically different chemical reactions. The causes and cures of lost cell electrical capacity are different between the two types of cells. However, this method of diagnosing which cells are sick, and how badly they are affected, is just the same for both lead-acids, nickel cadmium (nicads), and nickel-iron cells. This diagnostic technique uses electrical measurements to identify which cells have lost capacity and quantifies the cell's loss in capacity. If you don't know the battery basics such as capacity and voltage and so on, please read the article entitled Battery Basics in HP #27, page 30.

Don't Panic

Most users who suspect that their battery has lost capacity, in fact, have nothing to worry about. This perception, which commonly occurs to PV users during the winter months, is untrue. A battery is like a bucket. If

36 Home Power #28 • April / May 1992

©1992 Richard Perez

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