Virtual Mechanic

A Simplified Approach To Battery Charging
The rules that apply to battery charging need not be complicated.  Put simply, a battery eventually reaches a state of discharge and must be restore to peak performance.  When a charger is connected to a discharged battery, most of the charging current converts the battery’s active material back into its former fully charged state.  However, when the battery reaches about 80% of charge, charge efficiency reduces significantly.  At this point the electrolyte begins to break down into gas and as a result internal temperature increases.
When vigorous gassing begins, the charge rate should always be reduced.

Basically, there are two types of chargers designed to make battery charging safe and efficient; Constant current chargers and Constant voltage chargers.

A constant current charger maintains a relatively constant charging current throughout the recharge process.  In reality the charging reduces as state of charge increases.  However, the charger resists the tapering effect.  Most off the shelf chargers are of the constant current type.  Some have a number of charge settings to allow for fast or slow charging.  Constant voltage chargers maintain a steady charging voltage.  When connected to a flat battery the charger  works at maximum output.  As the battery state of charge increases the charge rate automatically reduces to a lower rate.

When operated at correct charging voltages, constant voltage chargers reduce the risk of accidental overcharge.  The alternator/regulator combination within a motor vehicle provides another constant “built-in” voltage charging source.  Today’s batteries are designed to offer consumers more safety, security and performance for a lot longer than ever before.  However, without proper care and maintenance a battery’s original life may be significantly reduced.

Charging a battery
Before charging begins, provide plenty of ventilation and ensure safety goggles and a face shield are worn.  Explosive mixtures of hydrogen and oxygen gases are present with the battery cells at all times.  Even a battery standing idle generates small quantities of hydrogen due to the self-discharge action.  Gas collects in the cells and can be set off by sparks, flame or a lighted cigarette.

Sparks from loose connections or metal tools making contact between the terminals or the ungrounded terminal and nearby grounded metal parts can also be hazardous.

Do not remove the vent caps and do not charge the battery unless you are thoroughly familiar with the step-by-step procedure to use.  Follow the manufacturer’s instructions on the charger.  If the instructions are no longer legible, they may be obtained from the manufacturer of the charger.  Never use a charger without instructions.

First check the electrolyte levels then, place a wet cloth over the battery top and vent caps.  Turn the charge rate switch and timer to the OFF position before connecting the leads to the battery.  Next, connect the charger leads to the battery terminals, red positive (+) lead to positive terminal and black negative (-) lead to negative terminal.  Rock the charger lead clamps to make certain a good connection has been made.  Set the electric timer to the desired charging time.

Now, turn on the charger and slowly increase the charging rate until the desired ampere value is reached.  Do not charge in the red zone.  If the battery starts to emit smoke or dense vapour, shut off the charger and reject the battery.  If violent gassing or spewing of electrolyte occurs, reduce or temporarily halt the charging.

Never touch the charger leads when the charger is ON.  This could break a connection at the battery terminal and create a spark which could ignite the explosive gases in the battery.

Never break a “live” circuit at the battery terminals for the same reason.  Always turn the charger OFF before removing a charger lead from the battery.

Battery Charging

This article is found in the Virtual mechanic CD Rom
You can download it for the price of a latte, but you will learn not to buy a lemon
By Darren Gow-Brown, Melbourne Australia ©2009

Batteries must be subjected to regular testing to ensure their starting capacity is maintained at an optimum performance level.  A battery must also be scrutinised for any physical condition which may reduce battery life and impede starting performance such as broken or damaged posts and leaks to the battery case or lid

The first step in evaluating starting capacity involves testing a battery’s state of charge using a hydrometer or voltmeter.  All non-sealed batteries should be checked using a hydrometer.  As a cheap and reliable method of determining state of charge, the hydrometer also reveals differences between cells and allows visual inspection of the electrolyte colour.  Where the hydrometer reading shows no significant difference between cells and produces a reading of 1230 or above (at 20-25C) the battery has sufficient charge for a load test.

Sealed batteries must produce a voltage of 12.5 or greater before a load test may be performed.  Since the loss/fail criteria varies depending on the make of load tester used, be sure to consult the instruction manual provided with the tester to ensure success.

Battery Testing

This article is found in the Virtual mechanic CD Rom
You can download it for the price of a latte, but you will learn not to buy a lemon
By Darren Gow-Brown, Melbourne Australia