What you should know about batteries Battery Types Battery Cycles Battery Chargers Battery Connections How to select your battery size	Charging Multiple Battery Systems Connection Diagram CDR200 (Charger Distribution Relay) LEAB EDR (Energy Distribution Relay) 'Low Drop' Battery Isolators	LEAB DC/DC Booster 12 V DC to 14.4 V DC - 12A LEAB DC/DC Booster 24 V DC to 28.4 V DC - 8A

What is a battery?

A battery can simply be described as an electrochemical device that stores energy in chemical form. When it is attached to a consumer the chemical energy is transformed into electrical energy.

All batteries consists of one or more cells. Each cell is built up of positive and negative electrodes, with a separator and an electolyte. The most common are lead acid batteries which have a nominal cell voltage of 2 Volts. A 12 Volt battery consists of 6 cells connected in series.

The active material in the positive electrode consists of lead dioxide pasted on a gitter plate.

In the negative electrode the active material is a porous, fine grained metallic lead pasted on a gitter plate. The gitter plates are, in wet batteries, made of an alloy of lead and antimony and in gel batteries of a lead-calcium alloy. Antimony will slowly be released from the gitter alloy when the batteries are used, which will increase the gassing voltage. The gassing voltage of the battery charger used should thus if possible also be adjusted accordingly.

The electrolyte is a diluted sulphuric acid, either as a liquid (wet batteries) or in a gelled (gel batteries) state.

These components are put together in different ways to create batteries suited for various tasks.

Function of the battery

When a battery is discharged or charged an electrochemical process involving the active material of both electrodes takes place. At discharging, lead sulphate is built up on the negative as well as the positive electrode at the same time as energy is emitted. When charging energy is supplied the chemical process is reversed. The lead sulphate returns into the original lead dioxide and fine grained lead. This process must be as complete as possible in order for the battery to become fully charged. If the battery is over charged, water is consumed and a highly explosive mixture of hydrogen and oxygen gas is produced.

AREA OF USE

Stationary batteries

Stationary batteries are used drawing low and often intermittent current during extended periods of time eg as emergency power, emergency lights and warning devices. The number of cycles (complete charging - dis- red. charging) are often low. They are on permanent maintenance charging and must be designed for low corrosion of the electrodes.

Starter batteries

Starter batteries must be able to give a high current for a short time without dropping too much in voltage. They must manage a great number of shallow discharges but not so many complete cycles. To be able to give a high current for electrode area, and short distance between the electrode plates together with substantial cell connections. Used as the name implies to start engines.

Should these batteries be used as consumer batteries the positive electrode will prematurely be destroyed due to deposit build up at the bottom of the battery vessel.

Traction batteries

Traction batteries are made for a low current draw, in comparison to the capacity of the battery, during a long time and to a high level of discharge.They must also manage a large number of cycles. To achieve this traction batteries have thick electrodes and an abundance of active material. Traction batteries are used for fork lift trucks and other battery driven vehicles.

Leisure batteries

Leisure batteries are designed as something in between traction and starter batteries. Most of the time they are used with a low current draw and a high level of discharge during many cycles but must also be fit for use as a starter battery~ Usage eg. in caravans and leisure boats. Solar batteries also falls into this category.

Batteries can be classified either according to how they are built or according to the area of use they are designed for.

Open or Wet batteries

This is the original battery construction. This type requires repeated maintenance because hydrogen and oxygen are emitted from the battery when overcharging. When these two gasses are mixed an explosive gas is formed. Charging should take place in well ventilated areas. The fluid must be checked and refilled when the level sinks to compensate for the gassing. What is not readily noticeable is the corrosion of the electrodes. Over-or undercharging will reduce the life of the battery.

Valve regulated batteries

In valve regulated, or recombination batteries as they are sometimes called, the gas generated at charging is recombined into water. This is done through channelling the gas back to the negative electrode, where it is recombined into water before it can escape from the battery. This means that no maintenance is necessary. At uncontrolled overcharging a safety valve will open and let the gas out. Even if it should be a small amount of gas and the risk of explosion is small, the battery will still be damaged since it is not possible to replenish the electrolyte.

Gel batteries

These types of batteries have their electrolyte gelled. Otherwise they are a special type of valve regulated batteries. These batteries should only be charged using a high quality charger with temperature controlled voltage regulation to achieve a long service life.

The gelled electrolyte reduces the gassing by a factor 10 compared to wet batteries. Specially ventilated areas for charging are thus not required. Gel batteries are sealed and have good storage properties.

A component of the electrolyte is phosphoric acid. It will improve the cycle properties and facilitate recharging after a battery has been deep discharged. The gel batteries have good charging-discharging cycle properties and will not, when mechanically damaged, leak electrolyte. A temporary deep discharging will not destroy these batteries.

Discharging

The energy that a battery produces can be specified in different ways, depending on what purpose the battery is used for. Starter batteries are often specified in CCA or Cold Cranking current in Amperes (Amperes a battery will deliver for 30 sec in -18°C without the voltage dropping beneath 1.2 V/Cell). For other types of batteries the most common denomination is Ampere hours (Ah) which specifies how many Amperes the battery can give in a certain time without voltage falling below a specified value. The capacity for Leisure batteries are mostly given as C20, which means the rate in Amperes a battery will deliver for 20 hours with the voltage not dropping below 1.75 V/Cell. If a battery under these conditions delivers 4 Amps it means that the capacity will be 4Ax2OHrs = 8OAh. Batteries used for industrial purposes are often designated using the CS capacity. This means that an 80 Ah battery will give 16 Amps for 5 hrs. The same battery would, if discharged with a fixed current for 20 hrs give a higher current than 4 Amps. The level of discharge current thus has an influence on capacity, a higher rate of current means a lower capacity rating. Also the temperature will have an influence on capacity, a higher temperature on the battery, within limits, will give a higher output.

Charging

The efficiency of the chemical process in the battery means that the energy supplied must be bigger than the useful energy output from the battery. It is important that the batteries get exactly fully charged. All the lead sulphate must be processed into lead oxide in order that the electrodes do not sulphate, which is what happens if the battery is undercharged. If the battery is overcharged water is lost through gassing, which will cause corrosion of the electrodes. Overcharging can also cause the temperature inside the battery to rise above allowable level and damage the battery.

The battery state of charging can be measured using an acid tester, that will measure the specific gravity of the battery fluid. Another way is to use an accurate voltmeter. A sealed Lead-Acid battery can only be controlled using the voltmeter.

Measuring the state of charge of a battery using an acid tester (at +25°C).

Fully charged battery 1.28 kg/I of battery fluid
50% charged battery 1.20 kg/I of battery fluid
Empty battery 1.10 kg/I of battery fluid

Measuring the state of charge of a battery using an accurate voltmeter (at +25°C).

To be able to relate the voltage to the state of charge the battery must have rested (no charging or discharging) during the last 4-5 hours before measuring. Thus the equilibrium voltage is achieved (balance).

Values below are valid for l2V batteries (For 24V double all values).

Fully charged battery 12.7 Volt
50% charged battery 12.3 Volt
25% charged battery 12.1 Volt
Empty battery <10.0 Volt

Measuring the state of charge of a Gel battery using battery test instrument.

The state of charge of a Gel battery can also be determined by measuring the battery voltage a fixed time after applying a predetermined load. Using this method the state of charge as well as the capacity of the battery can be determined.

Next the equilibrium voltage is measured using the test instrument. Thus a rough idea of the battery status is determined. A possible short circuit can also easily be proven.

If the equilibrium voltage is less than 12 Volt the battery is either defective or deep discharged. The battery must then be charged for at least 48 hours. If the equilibrium voltage is below 12.5 V the battery must be charged for at least 16 hours. The load test can be done immediately when the equilibrium voltage is 12.7 V.

After measuring the equilibrium voltage and if necessary charging the battery, the load test is done. The test instrument is set at the appropriate resistance (ace. to battery capacity) and the test probes are firmly pressed to the battery poles. If the resulting voltage is above 10 V the battery is OK. However if it is below 10 V the battery is defective and must be changed.

A battery charger can be built using several different types of technique giving different end products What should be chosen depends on area of use, type of batteries to be charged and power source used. The power source is most of the time mains supply but can also be gensets, alternators and wind generators. Below is a comparison of properties of the main types of chargers for Lead-Acid batteries.

Transformer charger - unregulated The unregulated transformer charger is the least complicated and cheapest charger on the market. The charging voltage varies with the input voltage and with the state of the batteries being charged. This means that the charging voltage sometimes becomes so low that no charging takes place and sometimes so high that the batteries will be overcharged, resulting in damaged batteries. This type of charger should never be used without supervision and only for temporary charging. They are mostly used for charging starter batteries that accidentally have been drained. Unregulated chargers means risk of overcharging

Transformer charger - regulated

The regulation of these chargers prevents overcharging. They can be connected and left without supervision for extended time. The regulation varies considerably between different brands. Regulator settings that never charge the battery fully are not uncommon. If the supply voltage drops too much, it can be difficult to achieve a fully charged battery. Regulated transformer chargers are used for leisure batteries, traction batteries and stationary batteries with regulation adapted to the specific type of battery they are intended for.

Simple regulated primary switch mode chargers

These chargers are designed with the size and weight advantage of the primary switch technique and are thus light and compact. They will also have the advantage of not being affected by input power variations. In general they have a simple fixed charging characteristic (eg. IU) without the flexibility necessary to charge the batteries 100% full. A charging characteristic with time constants with no means of taking simultaneous consumption into account will make the charger switch off or switch over to trickle (maintenance) charge too soon.

Advanced primary switch mode chargers

This type of charger is a fully electronic charger with free adjustable charging characteristic that will give a fast efficient and reliable charging for every type of battery and every mode of usage. Overcharging does not exist and the charger will not be affected by variations in frequency or shape of the input current. Input voltage can also vary within a considerable range and still give correct output voltage and full output current. The output current has a very low ripple (AC component on DC) which means that they can also be used to charge solid electrolyte batteries (Gel-batteries). Advanced switch mode chargers have low weight and low volume in comparison to the charge. They are also quiet (no humming) and develop little heat due to high efficiency. This makes them suitable both as free standing and on-boardchargers. These chargers are used for all types of batteries

Parallel Connection When connecting the batteries in parallel the positive poles are connected to each other as are the negative poles. The voltage does not change and the capacity (Ah) will be the sum of the connected batteries.		Example: Two batteries each 12V/80Ah connected in parallel will result in 12V/160Ah
Series Connection When connecting the batteries in series the positive pole of one battery is connected to the negative pole of another battery. The voltage will be the sum of the connected batteries voltage and the capacity (Ah) will remain the same.		Example: Two batteries each 12V/80Ah connected in series will result in 24V/80Ah
Parallel-Series Connection Both types of connections are used. The parallel connection will raise the capacity (Ah) while the series connection will raise the voltage.		Example: Four batteries each 12V/80Ah connected in series - parallel will result in 24V/160Ah

Battery capacity The capacity of the battery is stated in Ah (Ampere hours) and varies with the amount of current (A) that is drawn from the battery. For leisure batteries the 20 hour capacity is mostly used, ie a battery with 80 Ah can during 20 hours give a constant current of 4 A before the voltage has dropped below 1.75 V/Cel I. A higher current than 4 A, means that the battery will give less than 80 Ah, and a lower current than 4 A means that the same battery will give more than 80 Ah.

Dimensioning of batteries The choice of battery capacity is determined by the demand and the time between recharging. The demand of the consumer is stated in Watts. Since the capacity of the batteries is stated in Ah, we have to recalculate the consumption and make into Ah according to the formulae below. Example: In a 12 volt system there are light bulbs consuming a total of 60 Watts. They are used in total 4 hrs between each charging of the batteries. This means that the light bulbs consume 60/12=5A (formula 3), which means that the capacity demand will be 5x4=20 Ah (formula 4). The capacity demand of all consumers is calculated and added to give the total demand. If the total demand has been calculated as 100 Ah, you use a safety factor of 1.3 for Gel batteries and 1.7 for wet batteries. This corresponds to a choice of a 130 Ah Gel battery and a 170 Ah wet battery.

Choice of battery charger size Most battery manufacturers recommend that their batteries should be charged using a charger that in A will give between 10 to 30% of the battery capacity in Ah. Because of this, most regulated battery chargers are designed for battery sizes somewhere in that range. This means that for example a 15 A charger should be used for batteries with a capacity of between 50 and 150 Ah. For some applications simultaneous consumption very often takes place during charging, by a refrigerator, lights or other electric equipment. This means that the consumers will use current that otherwise would have gone to the battery, and they will thus reduce the effective size of the charger. It is therefore important to consider this consumption when choosing battery charger size in order to get as good charging as possible.