Friday, August 15, 2014

Increasing performance of Battery; Electrolyte used in Batteries; Inverter Battery Charging

For better performance of Inverter Battery it is always recommended to follow the procedure as given below:-

There are following ways to increase the life and Performance of lead acid batteries:- 

1.     The most important part is the care during initial filling and charging which determines the life & performance and knowledge about how a lead-acid battery works
2.     There should be appropriate followed up proper and regular routine and preventive maintenance of the battery banks.
3.     To take corrective measures, one must have the knowledge of the normal failure modes of lead- acid batteries & the reasons for the failure.
4.     If any one is conversant of the failure mode and the reason for same, then will be in a position to rectify / prevent before it is too late.
Initial filling and Charging a Battery
General requirement

1.        Room in which batteries is kept should be clean, Dry, cool and properly illuminated and well ventilated. Batteries should be well cleaned before filling.
2.        Constant current of same rating as per requirement should be used which should be capable to supply requisite volt & amps designed to give at 6% rate of charge up to 2.75 VPC at to charging voltage.
3.        Sufficient quantity of battery grade sulphuric acid of 1.220 + 0.005 sp. Gravity at 27ºc conforming to be 266 & battery grade water conforming to be 1069 should be available. Some stock of 1.400-sp.gravity sulphuric acids at 27ºc for adjustment after full charging, if required.
4.        Don’t use the blind plugs supplied with batteries. Keep the vent plugs loose in position, to avoid explosions.
5.        Never ever use a Metallic vessel while filling always use plastic vessels and protective wears.
6.        Never take open flame near Batteries.
7.        Never connect the cable loosely with the cells / batteries to avoid sparks & chance of explosion / melting.
General requirement: Making dilute Acid
1.      If dilute acid prepared from concentrated acid at site, care to be taken. Do not use wooden or any other metal stirrer but to use plastic/lead instead of wood only to avoid contamination. Compressed air can be used for mixing but care should be taken to trap oil acid to be used.
2.      To follow all laid down safety rules for diluting acid from 1.840-concentrated acid.
3.      The acid to be used after cooling, specific Gravity corrected to 27ºc.
4.      Use ‘acifil pump’ or siphoning with spring loaded control lever trap, during acid filling to avoid spillage and surface / earth leakage.
Acid Filling Procedure:
1.        The battery should be checked physically for any damages/visible cracks and cleaned prior to filling of acid. Which may otherwise leads to explosion sometimes if there is problem in battery.
2.        Check the specific Gravity of acid prior to filling.
3.        Pour cool dilute battery grade sulphuric acid of 1.220/1.190 sp. Gravity up to the max. Level by ‘acifil pump’, siphoning pipe or with funnel & jug carefully. Do not over fill to avoid spillage.
Polarity check & Rest period Procedure:
1.      Just after acid filling, to check polarity of the cells by checking the voltage of all the cells, if any cell wrongly reverses assembled. The voltage observed is not that important at this point. Also check for any leakage visible after filling.
2.      Allow 12 hours rest for the cooling; allow the plates & separators to soak acid, but not more than 24 hours. Top up again with acid, same as filling- in sp. Gravity.
Putting on First Charge Procedure:
1.        Use only DC ‘constant current’ charger only for initial charging of batteries.
2.        Ensure the charger in working condition and capable of supplying requisite volt & amps required for the batteries to be charged.
3.        Take care of polarity and connect the pos. Terminal of batteries with the pos. & neg. Terminal with neg. Of the charger, respectively.
4.        Charging may be done in 2 steps or single step. In our tropical country advisable to charge in single step, especially in summer
- For ‘2 step charging’ the initial current to be 12% of the C10 capacity of battery upto 2.36 VPC and followed by 6% of the C10 rated capacity of the battery upto 2.75 VPC. (For 500Ah battery 60 amps & 30 amps respectively).
- For ‘single step’ charging, the battery to be charged continuously at the current 6% of the C10 rated capacity of the battery upto 2.75 VPC, till the end of charging e.g. 30 amps upto 2.75 VPC for a 500 Ah battery till end.
Condition of Fully Charged Procedure:
To continue DC charging at ‘constant current’ till the following conditions of fully charged cells are observed:
1.        All cells are gassing freely at voltage, 2.75 VPC at 6% - the finishing rate.
2.        No rise of voltage for 3 to 4 consecutive hourly readings, after reaching 2.75 VPC
3.        No rise of specific Gravity for 3 to 4 consecutive hourly readings, after reaching 2.75 VPC
4.        Theoretical Ah input to be kept at the back of the mind- the input to be approx. 4.5 to 5 times of the Ah capacity of the battery i.e. For a 500 Ah battery the total Ah input to be 2250 Ah to 2500 Ah. (approx. time 75 to 85 hours)
Checks & Record during charging Procedure:
1.        The electrolyte temperature should not be allowed to increase beyond 50ºc, during charging if the temperature goes above 50ºc, the charging to be suspended till the temp. of electrolyte comes down to 40º c, then only start the charging again.
2.        Record the readings of sp. Gravity, voltage and the electrolyte temp. of cells, initially every 4 hourly and every hourly, after the cell voltage reaches 2.4 VPC.
First C10 Capacity test Procedure:
Batteries now charged ready - give a rest period of 12 hours for cooling & settling but not more than 24 hours.
Connect the batteries with suitable load and conduct C10 capacity test at constant current, upto ‘end voltage’ 0f 1.85 VPC e.g. For a 500 Ah battery at 50 amps for 10 hours. Take hourly readings and record the volt, specific Gravity & electrolyte temp. Of all cells. If any cell voltage comes to 1.85 volt before 10 hours, the cell to be recharged / checked before taking for commissioning.
Recharge after C10 Capacity test Procedure:
Recharge the batteries immediately after discharge by constant current charging at 6% of the rated Ah capacity of the battery upto 2.75 VPC, till the batteries are fully charged- i.e. All cells are gassing freely, constant voltage, constant sp. Gr., theoretical 130% Ah   input given, when 100% of Ah taken out during discharged.
Adjustment of Sp. Gravity Procedure:
1.        After batteries are fully charged, the sp. Gravity of the electrolyte of all cells to be adjusted to the service gravity i.e. 1.210 /1.250 ± 0.005, at 27ºc. the batteries to be put on charge for proper mixing.
2.        If sp. Gravity in cells more than service gravity corrected to 27ºc. Take out acid and add battery grade water, when on charge for proper mixing. adjust sp. Gravity to the service gravity corrected to 270 c. As applicable with respective batteries.
3.        If the sp. Gravity of the cells less than the service gravity at 270 c take out acid and add 1.400 sp. Gr. Acid by few drops, on charge for proper mixing. Adjust the sp. Gravity to the service gravity at 270 c as applicable.
4.        After adjustment of the specific gravity, continue the charging for 1- 2 hours for proper mixing of the electrolyte. Stop the charging and allow the batteries to cool, before commissioning.
The normal failure modes of lead - acid batteries
Sulphation in cells
1.        Over discharge
2.        Allowing a battery to stand idle
3.        Starvation
4.        Allowing electrolyte to fall on earth
5.        Impurities in electrolyte
6.        Adding Acid instead of water.
Bucking of plates:
1.        Over discharge
2.        Continued operation with battery in starved condition
3.        Charging at high rates
4.        Non- uniform distribution of current over the plates, due to repeated deep discharge
Shedding of active materials:
1.      Normal Shedding
2.      Excessive Charging rate or Overcharging.
3.      Charging sulphated plates at too high rate
4.      Charging only a part of the plate
5.      Deep discharge battery on normal charge.
6.      Freezing.
Container trouble:
1.        Rough handling: any storage battery to be handled as if made of glass, though the containers made with hard rubber, SAN or FRP. Heavy batteries should be handled by more than one person or by mechanical handling and not to be dropped / dragged. This will lead container crack/ damage.
2.        Explosion in cell: may cause due to open flame, electrical sparks and clogged vent holes.
3.        Bulging of container: this is be due to under curing of the container.
4.        Stacking should be restricted to max. 3 high, with hard board in between layers
Terminals/ connector corrosion:
1.        Too much topping water added to cells
2.        Battery poorly sealed
3.        Loose vent caps / float guide
4.        Electrolyte spillage
5.        Battery cable damaged, or loose
6.        Connecting bare wires directly to battery terminals.
7.        Loose terminal connections
8.        Non application or renewal of petroleum jelly for protection
Loss of capacity:
1.        Impurities in the electrolyte
2.        Sulphation
3.        Loose active materials
4.        Incorrect proportions of acid and water in the electrolyte
5.        Separators clogged
6.        Shedding
7.        Low level of electrolyte
8.        Effect of age
Internal short circuit:
1.        Worn out separators
2.        Lead run
3.        Foreign material
4.        Accumulation of sediment
Reversal of plates:
1.        Assembling of the cell in reverse direction.
2.        Charging a battery in wrong direction.
3.        Lagging / defective cell in battery bank will be reversed if not taken care in time
Earth / surface leakage in battery:
1.        Over filling of battery water.
2.        Careless hydrometer use, spillage of electrolyte.
3.        Careless acid filling during initial filling & charging.
Problems in Electrolyte:
1.     Higher specific gravity of electrolyte.
2.     Lower Specific gravity of electrolyte.
3.     High Level of electrolyte.
4.     Lower Level of electrolyte.
5.     Impurities in electrolyte.
The importance of equalizing charge:-
To ensure that every cell in a battery bank is maintained in healthy state to give enhanced life & performance it is advisable to give ‘equalising charge’ atleast once in a year. Under ‘constant potential’ mode during operation a passive layers form on the plates. This causes variation of sp.gravity & voltage from cell to cell. To take care the battery bank to be put on ‘constant current charging at 6% of rated capacity upto 2.75VPC, followed by an extended charge for 12 to 24 hours on ‘constant current’ charging at 3% of rated capacity. By this the cells are rejuvinated with fresh layer of active material, all the cells will show approx. Same sp. Gravity & voltage. As low current was given during 3% rated amps of the Ah capacity. This will not affect the activated portion of the plates, but will remove the patches of sulphate from the plates back to the solution, increasing the sp. Gravity of cells. so, it is mandatory to give equalising charge, once in ayear,if not earlier.