The electrochemical reactions in a lead acid battery when discharged can be easily described with the following formula:

This reaction is reversible and when charged runs in the opposite direction to the above arrow.

1.2 Valve Regulated Technology for Lead-Acid Batteries

Main Characteristics

• Immobilised Electrolyte
• Pb-Ca-Sn-alloy

The sealed lead-acid batteries are maintenance free for three reasons:

• The Pb-Ca-Sn alloy guarantees the mechanical stability of the plates and increases the system gassing voltage to high values.
• The electrolyte is immobilised
• By closing the system with a valve, the released oxygen can recombine and reduce the production of hydrogen.

The electrolyte is immobilised either in a gel or by absorption of the electrolyte in a glass fibre separator. This is the AGM (= Absorbed Glass Mat) technology. The electrolyte in the dryfit batteries is immobilised in a gel.

1.3 Plates

dryfit batteries of the series A 200, A 300, A 400, A 500, A 700 and0GiV contain grid plates. These gravity cast lead grids, produced for positive and negative plates, are pasted with a lead oxide paste, cured and then formed. The positive plates for the series A 600 are tubular plates for which the dry raw material (powder) is vibrated into polyester gauntlets. The plates are then cured and formed.

• Active negative plate substance: Spongy lead.

• Active positive plate substance: Lead dioxide.

1.4 Separator

The separator separates the positive and negative plates mechanically and electrically from one another. It must not only guarantee a high porosity to allow electrolyte acceptance and ion migration, but it must also prevent short circuits.

The electrolyte in the dryfit batteries is immobilised in a gel (sulphuric acid: H₂S0₄). The gel is a mixture of sulphuric acid, water and SiO2. The gel system also offers the possibility of varying the components and to include certain additives for the cycle stability.

1.6 Water Loss and Recombination

When the battery is fully recharged water decomposition takes place causing water loss. In the valve regulated lead-acid battery the water decomposition is almost fully compensated by the recombination of the oxygen on the negative plates. This oxygen recombination is made possible by the immobilised electrolyte.

As the speed of diffusion of oxygen into sulphuric acid is very low, there is hardly any recombination in a conventional lead-acid battery. However, in batteries with the gel electrolyte system channels are formed through with the oxygen (which forms on the positive plate) can migrate to the negative plate without any interference. The dryfit system electrolyte reserve is regulated so that the service life is not influenced by the water loss.

1.7 Casing

The dryfit batteries are available with the following casing material:

• A 200, A 300, A 400 and A 500 Standard material : up to 16 Ah : Acryinitrile-butadiene-styrene-copolymer (ABS) for 20 - 200 Ah : Polypropylene (PP) Both materials are classified with normal flammability (UL94-HB).

As special type up to 16 Ah : Acryinitrile-butadienestyrene-copolymer (ABS) (UL94-VO) for 20 - 200 Ah : Polypropylene (PP) (U L 94-V2)

• 0GiV: Standard material Polypropylene (PP) (UL 94 HB)

• A600,A60OWEand A 700: Standard material :Styrene-acryinitrile-copolymer (SAN) (UL 94 HB)

ABS UL 94-VO on request.

2. Capacity

For the series A 200, A 300, A 400 and A 500 the nominal capacity is given for discharge at the 20 hour rate.

Discharge with constant current for the period of 20 hours corresponds to C_N. The final discharge voltage U_E with which the discharge is terminated is 1.75 V/cell.

• I₂₀ = C₂₀ / 20 h

(see also DIN 43539, Parts 1 and 5)

• All discharge currents are given in multiples Of I₂₀.

For the series A 600, A 700 and 0GiV the nominal capacity is given for discharge at the 10 hour rate. The final discharge voltage U_E for the nominal capacity C₁₀ is 1.8 V/cell.

• I₁₀ = C₁₀ / 1 0 h

The nominal capacity of solar batteries is given at the 100 hour rate, C₁₀₀ (final discharge voltage 1.85 V/cell) and the series A 500 C nominal capacity is given at the 5 hour rate, C₅ (final voltage 1.7 V/cell).

The capacity of valve regulated lead-acid batteries depends on the temperature and the output current (cf. fig. 2).

Discharge within the electrolyte-freezing zone could lead to destruction of the battery.

The final discharge voltage and discharge times, as well as the characteristic currents can be taken from the discharge curves in the brochures on the respective series. The discharge curve for the A 500 is given below as an example (cf. fig. 5).

3. Nominal Voltage

4.1 Final Discharge Voltage

The final discharge voltage is specified as the value below which the voltage must not fall when discharge occurs at the respective current. If the battery is discharged further, (i.e. the battery voltage is lower than the final discharge voltage), the area of deep discharge is entered. The final discharge voltage is normally given in V/cell and depends on the discharge current.

• U_E (battery) = n . U_E (cell)

N = number of cells (battery nominal voltage divided by 2 volts)

 

 

4.2 Discharge Current

The discharge current in multiples n I₂₀ or I₁₀ for a 1_X, current can be determined using the following formula:

n =  1_X . 20 h or  n = 1_X. .10 h

  C₂₀                            C₁₀

The following maximum discharge currents are stated in the series brochures for the dryfit batteries :

• The given maximum battery load is the maximum discharge current for continuous output.

• The given maximum current for 5 sec is used for dimensioning the battery fuse.

4.3 Depth of Discharge

The capacity taken from the battery is termed as the depth of discharge. For example, if 80% of the nominal capacity is used from the battery then the depth of discharge is also 80%.

The maximum permitted depth of discharge depends on the level of the discharge current and the temperature.

4.4 State of Charge

An approximate determination of the state of discharge by measuring the open-circuit voltage is possible with a tolerance of about 15% (cf. Open circuit voltage, fig. 4).

4.5 Deep Discharge

The battery enters the deep discharge zone when :

• discharge is continued below the given point of final discharge voltage, e.g. when continuous loads are not switched off during laid-up periods.

• the battery regenerates due to intervals during discharge so that when the final discharge voltage is reached the depth of discharge is too low.

In accordance with DIN 4353 9, Part 5, the deep discharge test is defined as follows : A battery having at least its nominal capacity is bridged with a load resistance. The load resistance is selected so that the discharge current with a cell voltage of 2V/cell lies in the range between 2. I_N and the maximum permissible discharge current. The battery is stored at room temperature for 30 days. At the end of the storage period the battery is charged for 48 hours. The following capacity test must show a capacity of over 75%.

• After this recharge dryfit batteries reach between 90 and 100% of their nominal capacity.

During the discharge of lead-acid batteries the acid density decreases giving a low conductivity for deep discharged batteries. This effect is compensated for in dryfit batteries by additives to the electrolyte which increase conductivity. A surplus volume in the plates is formed by increased lead sulphate formation, which represents a mechanical load for the system.

dryfit batteries are constructed to withstand the increased load largely without damage.

Deep discharge should be avoided.

Sulphation of the plates con also occur if the batteries are discharged with discharge currents < 0,2 . I₂₀. The batteries can then only be charged with a suitable charge process e.g. a charge with the IUI-characteristic (cf. fig. 8).

4.6 Discharge Voltage

5. Charging

dryfit batteries can be charged with the most simple recharging methods.

5.1 Charging Characteristic

Constant Voltage Charging

Fig. 6 U-Characteristic

The battery limits the charge current when under constant voltage charge the easiest kind of charge for dryfit batteries. The battery lowers the charge current with increasing charge level.

• dryfit batteries are generally charged with constant voltage.

IU-characteristic Charging

Fig. 7 IU-Characteristic

The IU characteristic is the most suitable characteristic for charging dryfit batteries and for valve regulated lead-acid accumulators. It is also recommended for valve regulated lead-acid batteries. The battery is first charged with constant current until the recommended charge voltage is reached. The voltage is then maintained constant and the battery limits the charge current as with the U-characteristic.

IUI-characteristic Charging

Fig. 8 IUI-Characteristic

For applications in cycle operation, where a maximum charging time of 16 hours must be guaranteed, the IUI-characteristic charging is recommended.

The IUI-characteristic is an extension to the IU-characteristic. When the current reduces to a certain value, this current is constantly charged until the charging equipment is switched off.

Here the following recommendations must be adhered to :

I_{1 :} 2 - 6 . 120

U_{1 :} see selection table p. 17

I₂ 0.24 . I₂₀

*Switch-off after a maximum of 4 h.

Fully charged condition

5.2 Charging Voltage

The charging voltage is determined by the recommendation given by the manufacturer for each battery type.

Fig. 9 A200/300 charging.	Fig. 12 A500C Charging.
Fig. 10 A400 charging	Fig. 13 A600, A700, OGiV Charging.
Fig. 11 A500 Charging	Fig. 14 Heavy charging for A400, A600, A700, and OGiV

5.3 Temperature Compensation of Charging Voltage

Temperature compensation of the charge voltage is necessary when the temperature fluctuates, to avoid increased gassing at higher temperatures.

We recommend the following temperature compensation

• Standby parallel operation below 15⁰C and above 25⁰C.

• Cycle operation below 10⁰C and above 30⁰C.
• Battery charging is not allowed above +50⁰C.

• When charging the battery below +5⁰C substantially longer recharge times must be expected, as the chemical reactions are very slow and the charge factor is increased up to 60%.

5.4 Recharge Time

Fig. 15 Examples of charge current and recharge time for various states of charge for the A500 series at 20C.

5.5 Charge Currents

We recommend the following nominal currents for dryfit batteries

• Standby-parallel operation: 0.1 to 0.2 A/Ah. resp. 2 . I₂₀ - 4 . I₂₀ (1 . I₁₀ - 2 . I₂₀)
• Cycle operation: 0.2 to 0.4 A/Ah. resp. 4 . I₂₀ - 8 . I₂₀ (2 . I₁₀ - 4 . I₂₀)
• Overcharging is to be avoided:

-by adhering to the IU-characteristic with temperature compensation.

-by adhering to the recommended charge currents.

-by limiting the ripple current.

• dryfit batteries are proof against continuous charging in standby parallel operation when the given charge conditions are adhered to.

6. Open-Circuit Voltage

7. Series and Parallel Connection

• dryfit batteries of an equal capacity can be connected as a serial arrangement.

• Parallel connections of serial arrangements are possible without a network to the batteries of the serial arrangement. It is sufficient to connect together the series connected batteries at the plus and minus connectors. EUROBAT, an association of battery manufacturers and users, recommends a parallel arrangement of a maximum of four strings.

8. Permissible Ripple Current

• A 200, A 300, A 400, A 500 The maximum permissible ripple current for cycle operation (charge and discharge) is 0.1 . C₂₀. The maximum allowed ripple current for a 24 Ah battery is, therefore, 2.4 A.

• Should the batteries be used in FLOAT operation, the maximum ripple current of 0,05 . C₂₀ must not be exceeded. The maximum allowed alternating current for a 24 Ah battery in this case is 1.2 A.

• A 600, A 700 and 0GiV in standby parallel operation: 5 A/100 Ah.

Permissible ripple current causes warming of the battery. During charging the temperature increase is not to exceed 3⁰C.

When installed in containers, cabinets, etc. the VDE 0570, Parts 2 and 7, must be adhered to, as

hydrogen in a volumetric concentration of more than 4% forms an explosive mixture. dryfit battery

gassing is extremely low. The required maximum gas volume of 30 ml per 1 Ah and cell in 30 days for

the series A 200, A 400, A 500, A 600 and A 700 in the proposed IEC 896, Part 2 (currently a draft) is

adhered to.

9.2 dryfit Battery Transport

Based on tests the following regulations have been specified for new and used dryfit batteries :

Dangerous Goods Regulations for Road Transport (German GGVS) : 'dryfit batteries are not classified as dangerous goods"

Dangerous Goods Regulations for Rail Transport (German GGVE) :

"dryfit batteries are not classified as dangerous goods"

Dangerous Goods Regulations for Air Transport IATA/DGR:

'dryfit batteries are not classified as dangerous goods'

Dangerous Goods Regulations for Sea Transport (German GVV See): "dryfit batteries are classified as dangerous goods, Type 8, UN-NR. 2800. Wet batteries, leakproof'

9.3 Storage

When dryfit batteries are stored fully charged

• the storage temperature is -,40⁰C to +50⁰C

• the maximum storage time is 2 years at 20⁰C

• at a constant storage temperature of 30⁰C recharge is to be carried out after 12 months, at 40⁰C after 6 months.

10. Service Life

The service life for dryfit batteries in constant charge operation, is the period of time after which the battery has only 80% of its nominal capacity C₂₀ i.e. C₁₀. This is valid for discharge at I₂₀ up to U_E = 1.75 V/cell i.e. I₁₀ up to U_E = 1,8 V/cell at room temperature.

The service life of the battery is an important factor for the standby parallel operation.

The service rife of the battery depends on the temperature and can only be reached if the given charge voltage is adhered to.

The diagrams show the service life in relation to the temperature.

Other parameters with influence on the service life are :

• charge voltage

• any deep discharges

• discharge frequency

• permissible ripple current

11. Cycle Endurance

Apart from the service life, the cycle endurance is also defined. The cycle endurance is applied when the battery is not used in standby parallel operation. Currently, the standard definitions are to be applied according to the following controls:

• Testing of the cycle according to DIN 43539, Part 5: The test is to be carried out on batteries which have reached their nominal capacity. Discharge is to be carried out with 3.4 . I₂₀ up to U_E = 1.7 V/cell. The calculation of the number of cycles is terminated when the discharge time has dropped below 3 hours.

• Testing of the cycle endurance according to IEC 896, Part 2 The test is to be carried out on batteries which have reached their nominal capacity. The discharge is 2 . I₁₀. Discharge time is 3 hours. A capacity test is to be carried out after each 50 cycles. The test is terminated when the battery has less than 60% of its nominal capacity.

The number of cycles which a battery can perform, depends on the battery construction and the depth of discharge.

12. Self-discharge

dryfit batteries have an extremely low self-discharge. This is a positive characteristic of the gel technology.

Fig. 22: Self discharge in relation to temperature for the A600 battery.

To calculate the RIG total resistance of the battery the following formula is valid at room temperature (20-25⁰C) for a in a fully charged condition.

The internal resistance depends on the temperature and the state of charge.

Fig. 23: Correction factor K for R in relation to the state of charge and temperature, for the series A200, A300, A 400 and A500.

*Series A600 WE: The series A600 is available for horizontal installation as A600WE

** 2.27 V recommended.

• Service life : 4 - 5 years
• Cycle Durability DIN/IEC: 200/400
• EUROBAT classification :Standard Commercial
• DIN VDE 01 08, Part 1; Application classification E
• UL: >>yellow card<< MH 12546

   

A300 Series

• Service Life : 4 - 5 years
• Cycle Durability DIN/IEC: 100/200
• EUROBAT classification : Standard Commercial
• DIN VDE 0108, Part 1 ; Application classification E
• UL: >>yellow card<< MH 12546

• Service life : 10 years
• Cycle Durability DIN/IEC: 100/200
• EUROBAT classification :High Performance
• DIN VDE 01 08, Part 1; Application classification Z
• BP Telekom, TL 6140-3003

• Service Life : 5-8 years
• Cycle Durability DIN/IEC: 300/600
• EUROBAT classification : General Purpose
• Types available with VdS classification
• DIN VDE 01 08, Part 1; Application classification E and A

• Service life :according to cycles
• Cycle Durability DIN/IEC400/800
• EUROBAT classification :none

A 600 / A 600 WE Series

• Service life :15 - 18 years
• Cycle Durability DIN/IEC450/900
• EUROBAT classification :High Integrity
• UL: >>yellow card<< MH 12546
• available for horizontal installation (WE)
• German Lloyd
• Bureau Veritas

• Service Life :12 years
• Cycle Durability DIN/IEC160/320
• EUROBAT classification: High Integrity
• DIN VDE 01 08, Part 1; Application classification Z
• UL: >>yellow card<< MH 12546
• German Lloyd
• Bureau Veritas