Batteries - Explosive gasses and Ventilation.

For general  guidelines on

Please see Appendix A 1 of   GelHandbookPart2.pdf  ( Rev 5. Dec '03 posted here Mar '04) 

 Basic principles and design  overview -  GelHandbookPart1.pdf  (Rev 1. Dec '03 posted here June 04)

--------------------------------------------------------------
The remainder of this page contains only general gassing information from older application manuals.

While the art of low-gas production type batteries is well advanced, using  Low Gassing Lead/Calcium plates and gas recombination techniques with well regulated charging devices, we CANNOT assume that the charging devices will always regulate voltage properly at all temperatures; Nor can we assume that necessary and routine  maintenance of the cabling  connections has been performed in a series/parallel battery set for mobile or Marine application. Given these variables, we must always design a suitably ventilated system in the event of charging induced gassing. For this reason it is strictly forbidden to use any battery technology in a sealed box or un-ventilated room. Ventilation to outside air- whether active (forced air) or passive (air slots or limber holes)- is compulsory.

ANY rechargeable battery can and will produce gas. Ventilate to outside air!

Caveat.The production of Hydrogen gas is not the sole reason for an explosion. There is a much greater need for a spark. The greatest danger of generating a detonating spark, arises from improperly secured battery terminal clamps, and from inflexible battery cables which come loose from the battery and so cause an electric spark. Batteries must be secured against motion, and the cables supported properly. Use of solid bar connectors in any motive or mobile battery application is prohibited. Well supported, good quality flexible cable or wire of suitable size will help absorb any minor motion or vibration and remove strain from the terminal connections where a spark is most likely to occur. NEVER use or mount any spark producing device in the battery chamber or box. ( Don't even think about it and if you've done it, change it before your friends are comforting your widow in certain ways not acceptable to thee..) 

Gassing in open or flooded lead acid batteries.

Theoretically, Hydrogen is only caused by an over-load current.  So long as a rechargeable battery is close to full charged, the fed-in current (i.e., the charging current) will be converted into electrochemical energy. In fact, however, certain quantities of hydrogen and oxygen are generated in a rechargeable battery at any time, and that means both when charging and discharging - even when inoperative!

Even when the so-called water decomposition voltage of 1.55 V per cell has not been  reached (e.g., in open nickel-cadmium batteries) a certain amount of hydrogen and oxygen is nevertheless released.  For this reason it is strictly forbidden to locate any kind of rechargeable battery whatsoever - even gastight nickel-cadmium batteries - in hermetically sealed spaces.  Potting them in resin is likewise strictly forbidden.

Most tactical vehicles are designed so that they can operate under battened-down NBC conditions.  This battened-down condition entails supplying air through filters to the crew compartment and battle station.  If batteries are accommodated in the crew compartment or battle station, the battery compartment ventilation air must also be supplied via the filter.

The amount of fresh air to be fed to the battery compartments is calculated using the following formula:

Q = V . q . s . n . I in liters/hours (1/h) (for open or flooded lead acid batteries)
where..
V = Dilution factor = 100 % / 3.8% > 26
The dilution factor indicates the quantitative ratio of air to hydrogen at which the explosive limit is not exceeded.
    q= Hydrogen volume in liters generated by each battery cell, Ampere and hour.
     In the case of open lead-acid batteries this is 0.42 l .
     In contrast, sealed gelled lead-acid batteries produce significantly less hydrogen. (This point is covered in more detail later in the text.)

s = Safety factor = 5 for land-based equipment and land vehicles.  For water vessels and boats s = 10.
n = Number of battery cells
I = Current in A, which causes generation of the hydrogen.
The stated ventilation equation can be simplified by combining the factors V q and s as follows:

For land-based equipment and land vehicles to
Q = 55.n.I in liters/hour (l/h)

For water vessels and boats to
Q = 110.n. I in liters/hour ( l/h )

For tactical land vehicles and military/naval vessels the current I, to be taken into account for ventilation measures equals 2 A per 100 ah  of the installed battery capacity. This assumes that the charging devices are restricted so that the so-called gassing voltage of the batteries, i.e., of lead-acid batteries, does not exceed 2.4 V/cell.  In the case of 24 V battery sets this figure is 28.8 V.

According to the above ventilation equation and quantity of fresh air equivalent to
Q = 55.n.I liters/hour = 55.48.10 liters/hour = 26,208 liters/hour = 26.3 cubic metres / hour.
must be provided for a 24 v 500 ah battery set comprising open lead-acid batteries. Powered or forced ventilation  therefore must be considered  compulsory during the recharging process for open or flooded batteries.

Gassing in Sonnenschein gelled electrolyte lead acid batteries, is far lower.

Dryfit battery gassing is extremely low.The required maximum gas volume of 30mL per 1Ah per cell in 30 days
for the series A200, A400, A500, A600 and A700 in the proposed IEC 896, Part 2- is adhered to.

We only recommend that the Sonnenschein™ or Deka™ Gel Cells batteries not be charged in a sealed container or environment. In normal usage these Manufacturers sealed, gelled Lead Acid batteries have no need to for special ventilation precautions. Ensuring that the air surrounding the battery bank e.g. via air slots (or Limber Holes) is in contact with the outside air, is sufficient. This opinion applies solely to Sonnenschein dryfit and Deka gel-tech.

CAVEAT.Gassing data are NOT available for Keystone™,Exide™ PV types, Dynasty™, Trojan™ or any other Gelled electrolyte brand and no opinion is offered.For the purpose of this ventilation discussion they are treated as wet or open vented batteries. Please study and follow specific manufacturers gassing data and ventilation requirements.

In contrast to open lead-acid batteries with liquid sulfuric acid electrolyte, sealed lead-acid batteries complying with VG 96 924 have a gelled electrolyte.
This gelled electrolyte allows capillary action connection channels to occur in it between the electrodes, and via which the gases generated by water decomposition can pass the opposite electrode, where they are consumed. (tech memo N 05 / 86)
That is to say, a gas consumption process occurs in sealed gelled lead-acid batteries.  This gas consumption increases with battery age, since more of the above-mentioned capillary connection channels form between the electrodes as the balance of its service life shortens.  However, this internal gas consumption action can only function up to a certain charging voltage, and thus up to a certain overload current.
Measurements have shown that when new sealed lead-acid batteries are continuously charged the following quantities of hydrogen and oxygen escape through the safety  valves:

After 2 years of use the above values reduce by a factor of 10.
Trials conducted on sealed lead-acid batteries 30 V 130ah VG 96 924 T 05 subjected to specific 19 hours recharging at a constant charging voltage of 2.37 V/cell demonstrate that:
During the charging operation the following amounts of gas escape from the complete battery assembly:
    New battery assembly:                        10 liters
    After 10 charge-discharge cycles:         4 liters
    After 150 charge-discharge cycles:       1 liters
The above is from Sealed lead-acid batteries / Military Applications - Sonnenschein-dryfit™
The quantity of escaping gas sub-divides into approx. 25% oxygen and approx. 75% hydrogen.
Gassing according to IEC 896/2-Oct 95 @ 2.3v / cell within 30 days was measured @ 5mL/cell/ah while Overcharging @ 2.48v/cell caused 900m L / cell / ah within 30 days!

 Therefore, when using these sealed, gelled Lead Acid batteries there is no need to take special ventilation precautions. Ensuring that the air surrounding the battery bank e.g. via air slots (or Limber Holes) is in contact with the outside air, is sufficient. Careful voltage regulation is compulsory for safe use and long life of the product!

The values found for the sealed lead-acid battery assembly 30 V 130 ah VG 96 924 T 05 ( A212/110 )can be applied to other sealed lead-acid batteries according to VG 96 924.That means that a maximum of 4ml of hydrogen per installed Ah of battery will be freed within 19 hours when recharging new-conditioned 24v battery sets at 28.5v.That equates to 1.6 liters from a 24v set comprising NBB 248 12v 100Ah VG 96 924 T 09 (A212/110 or Prevailer series-DF230 )in series parallel circuit.

  September, 2009        Sonnenschein contacts in  Australia   Asia    N & S America   Europe   Africa        
 
  N.America Tel 954 525 5557 Fax 954 522 3748 - Lauderdale Battery & Alternator, 2415 SW 3rd Ave, Ft Lauderdale Fl 33315