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Battery Safety

Batteries have the potential to be dangerous if they are abused.

Warning

Subjecting a battery to abuse or conditions for which it was never designed can result in uncontrolled and dangerous failure of the battery. This may include explosion, fire and the emission of toxic fumes.

WARNING - FIRE HAZARD

A Low voltage power supply is just as likely to cause a fire if a short circuit occurs as with any ether voltage. Please use suitable fuses or circuit breakers near the battery and between the battery and , any other power sources. Also ensure that electrical conductors such as metal objects cannot accidentally fall across the battery terminals.

Exploding Battery:

Batteries generate explosive gases during operation and when charging. Flames, sparks, burning cigarettes or other ignition sources must be kept away at all times.

Ensure that there are no loose metal objects around the batteries that can be blown down by a strong wind or knocked onto the battery terminals. Similarly sparks can be generated at the battery due to a poor connection.

Always shield eyes when working near batteries. Battery charging should be carried out in a well ventilated area - never in a closed room. Always, turn battery charger off before disconnecting a battery.

Acid Burns

Battery acid can cause burns. Use extreme care when handling acid. If electrolyte is spilled or splashed onto clothing or the body, wash with water and neutralize with a solution of baking soda and water.

Electrolyte splashed into the eyes is extremely dangerous. If this occurs, force eyes open and wash with clean cool water for five minutes and call a doctor.

A solution of l tablespoon of bicarbonate of soda to 1/2 litre of water should be kept readily available and in view near the battery bank. This solution will neutralize the acid and hence be a more effective eye-wash in the event of such an accident.

Topping Up

Otherwise referred to as electrolyte. The water used for diluting acid and for topping up must be free of mineral impurities. Distilled water, demineralized water, or rain water collected in glass or plastic may be used. Never use tap water as the effect of impurities is cumulative and detrimental to the battery.

NOTE: Do NOT add battery acid to the battery unless under the specific directions of a battery technician.

Placement of Batteries

Place batteries on a firm, solid and level support. Weight of batteries should be equally distributed over the base area. Batteries should not be in direct contact with a cold surface such as concrete. If the base of the battery stays cold, the acid will not mix readily and will tend to stratify (most concentrated acid at the bottom and least concentrated at the top). It is recommended that you use an insulating material such as rubber or vinyl under the batteries that will not be affected by the corrosive properties of battery acid.

Battery Connections

Make as few connections directly to the battery as possible. It is desirable to have a fully fused Distribution/Meter Box from which all other connections can be made.

Before making your connection to the battery, first smear petroleum jelly (eg Vaseline) over the terminal post to prevent or reduce the likelihood of battery acid creeping up the terminal post and rapidly corroding your connector. Make sure that the connector is fixed very firmly and that it is making good contact with the terminal post to reduce voltage drop.

Try to avoid increasing your battery capacity by connecting several small batteries in parallel. The more parallel connections there are, the more prone the system is to uneven charging due to lazy cells and unequal cell characteristics. This will cause an overall reduction in expected battery life and increase maintenance requirements.

External Safety Devices

Protecting the cell from out of limits operating conditions, either from the loads imposed by the intended application or abuse by the user or from unsuitable charging regimes, is a vital consideration.

All connections to the battery should be via suitable fuses or circuit breakers. Incoming charging connections are usually low current and should use low current fuses or breakers to suit the input source. Outgoing connections usually require higher rated devices. It is also recommended to incorporate a high current breaker close to the output of each battery system, before any distribution takes place.

Protecting The Battery

Over-discharging a Lead-Acid battery is one of the main causes of early failure along with leaving the battery discharged and lack of electrolyte.

Heat is also a big killer of all types of batteries and this is most likely to be due to unsuitable charging methods or procedures, see the section on Charging for more information about safe charging. Chargers are not the only culprits, overloading the cell during discharge also causes overheating.

Many safety devices are therefore based on sensing the cell temperature and isolating the cell from its load or from the charger if the temperature reaches dangerous levels.

Heat damages a cell no matter what its source and a cell will suffer the same damage by being placed in a high ambient temperature environment as it would from improper use.

Apart from damage from overheating, a battery may be damaged from excessive currents and from over and under voltage. Suitable protection methods and how they are implemented are described in detail in the section Battery Protection Methods

DO NOT LIFT BATTERY BY TERMINAL POSTS!

The terminal posts connect directly to the plates of the cells, they have no mechanical strength and the battery can easily be damaged by using them for lifting. On large Lead-Acid cells and batteries doing so may even rip hem out of the casing!

Short Circuits and their Consequences

Short circuiting a capacitor or a battery is definitely not recommended as the destructive power unleashed is often seriously under estimated.

As an example, a 0.1Farad capacitor charged to 14 Volts will store 10 Joules of energy (E = ½ CV2 ). This may not seem very much, it is only 10 Watt seconds, but it is enough to punch a hole through aluminium foil creating a lot of sparks. 30 Joules is enough to weld a wire to a ball bearing. This is because the discharge period is very short, almost instantaneous, resulting in a power transfer of hundreds of watts.

Batteries store even more energy. For comparison, a fully charged 3.6 Volt, 1000 mAh mobile phone battery has a low internal impedance and contains 12,960 Joules of energy. Short circuiting these cells can cause extremely high currents and temperatures within the cell resulting in the breakdown of the chemical compounds from which it is made. This in turn can cause the rapid build up of pressure within the cell resulting in its catastrophic failure, with unpredictable consequences including the uncontrolled rupture of the cell or even fire.

By the same token, a single, fully charged 200 Ah, 2 Volt Lead-Acid cell (or the similar capacity from any other cell chemistry) contains 2,592,000 Joules of energy. Don't wait around to see what happens if you drop a wrench on the terminals!!

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