Sealed Nickel-Cadmium Batteries
Gassing occurs as a conventional battery approaches full charge, and increases during any overcharge due to electrolysis of water in the electrolyte by the current supplied but no longer being used in charging. The gas is released through the vent to prevent pressure build-up and this loss together with loss from evaporation makes topping UP necessary. While on charge, the active material of the plates is being changed, but when the change is complete and no further convertible material remains, the electrical charging energy starts to break down the electrolyte. Oxygen is evolved at the positive plates and hydrogen at the negative
Sealed batteries (Fig. 1.3) are designed to be maintenance-free and although developed from and having a similar chemical reaction to the open type, will not lose water through gassing or evaporation. The seal stops loss by evaporation and gassing is inhabited by modification of the plates.
Sealed cells are made with surplus cadmium hydroxide in the negative plate so that it is only partially charged when the positive plate is fully charged. Oxygen is produced by the charging current at the positive plate (40H ˉ2Hˉ2O+4eˉ+O2) but no hydrogen is generated at the negative because some active material remains available for conversion. Further, the oxygen from the positive side is reduced with water at the negative plate (2Hˉ2O+4eˉ+O2 40H ˉ) so replacing the hydroxyl ions used in the previous action. The process leaves the electrolyte quantity unaffected. The hydroxyl ions acting as current carriers within the cell travel to the positive electrode.
Sealed batteries will accept overcharge at a limited rate indefinitely without pressure rise. Charging equipment is therefore matched for continuous charging at low current or fast charging used with automatic cut-out to prevent excessive rise of pressure and temperature. Rise of pressure temp and voltage all occur as batteries reach the overcharge area but the last two are most used as signals terminate the full charge.
Friday, June 11, 2010
Marine Engine Q & A- Electrical-Nickel-Cadmium Battery Plates
Plates
The active materials for nickel-cadmium cells are improved by additions of other substances. Positive plates carry a paste made up initially of nickel hydroxide with a small percentage of other hydroxides to improve capacity and 20% graphite for better conductivity. The material is brought to the charged state by passing a current through it, which changes the nickel hydroxide to hydrated nickel oxide NiO(OH). Performance of cadmium in the negative plates is improved by addition of 25% iron plus small quantities of nickel and graphite.
Active materials may be held in pocket or sintered plates former are made up from nickel plated mild steel strip shaped to form an enclosing pocket The pockets are interlocked at their crimped edges and held in a frame. Electrolyte reaches the active materials through perforations in the pockets.
Sintered plates are produced by heating (to 900°C) powdered nickel which has been mixed with a gas-forming powder and pressed into a grid or perforated plate. The process forms a plate which is 75% porous. Active materials are introduced into these voids
The active materials for nickel-cadmium cells are improved by additions of other substances. Positive plates carry a paste made up initially of nickel hydroxide with a small percentage of other hydroxides to improve capacity and 20% graphite for better conductivity. The material is brought to the charged state by passing a current through it, which changes the nickel hydroxide to hydrated nickel oxide NiO(OH). Performance of cadmium in the negative plates is improved by addition of 25% iron plus small quantities of nickel and graphite.
Active materials may be held in pocket or sintered plates former are made up from nickel plated mild steel strip shaped to form an enclosing pocket The pockets are interlocked at their crimped edges and held in a frame. Electrolyte reaches the active materials through perforations in the pockets.
Sintered plates are produced by heating (to 900°C) powdered nickel which has been mixed with a gas-forming powder and pressed into a grid or perforated plate. The process forms a plate which is 75% porous. Active materials are introduced into these voids
Marine Engine Q & A- Electrical-Nickel-Cadmium Battery Gassing, Topping up,
Gassing
The gases evolved during charging are oxygen (at the positive plates; and hydrogen (at the negative plates). Rate of production of gas increases in periods of overcharge. When hydrogen reaches a proportion of about 4% and up to 74% it constitutes an explosive mixture. Good ventilation of battery compartments is therefore necessary to remove gas. Equipment likely to cause sparking or arcing must not be located or introduced into battery spaces. Vent caps are non-return valves, as shown diagrammatically (Fig. 1.2) so that gas is released but contact by the electrolyte with the atmosphere is prevented. The electrolyte readily absorbs carbon dioxide from the atmosphere and deterioration results because of the formation of potassium carbonate. For this reason, cell vent caps must be kept closed
Topping Up
Gassing is a consequence of the breakdown of water in the electrolyte. This together with a certain amount of evaporation means that topping up with distilled water will be necessary from time to time. High consumption of distilled water would suggest overcharging.
Electrolyte
Potassium hydroxide solution is strongly alkaline and the physical and chemical properties of potassium hydroxide closely resemble those of caustic soda (sodium hydroxide). It is corrosive, so care is essential when topping up batteries or handling the electrolyte. In the event at skin or eye contact the remedy is to wash with plenty of clean water (for 15 minutes) to dilute and remove the solution quickly. Speed is vital to prevent burn damage; and water, which is the best flushing agent, must be readily available. Neutralizing compounds (usually weak acids) cannot always be located easily, although they should be available in battery compartments.
Specific of electrolyte in a Ni-Cd cell is about 1.210 and this does not change with charge and discharge as in lead-acid cells. However, over a period of time the strength f. the solution will gradually drop and renewal is necessary at about a specific gravity of 1.170
Containers
The electrolyte slowly attacks glass and various other materials. Containers are therefore of welded sheet t which is then nickel plated or moulded in high-impact polystyrene casings are preferred when batteries are subject to shock and vibration. Hardwood crates are used to keep the cells separate from each 2t and from the support beneath. Separation is necessary cause the positive plate assembly is connected to the steel casing.
The gases evolved during charging are oxygen (at the positive plates; and hydrogen (at the negative plates). Rate of production of gas increases in periods of overcharge. When hydrogen reaches a proportion of about 4% and up to 74% it constitutes an explosive mixture. Good ventilation of battery compartments is therefore necessary to remove gas. Equipment likely to cause sparking or arcing must not be located or introduced into battery spaces. Vent caps are non-return valves, as shown diagrammatically (Fig. 1.2) so that gas is released but contact by the electrolyte with the atmosphere is prevented. The electrolyte readily absorbs carbon dioxide from the atmosphere and deterioration results because of the formation of potassium carbonate. For this reason, cell vent caps must be kept closed
Topping Up
Gassing is a consequence of the breakdown of water in the electrolyte. This together with a certain amount of evaporation means that topping up with distilled water will be necessary from time to time. High consumption of distilled water would suggest overcharging.
Electrolyte
Potassium hydroxide solution is strongly alkaline and the physical and chemical properties of potassium hydroxide closely resemble those of caustic soda (sodium hydroxide). It is corrosive, so care is essential when topping up batteries or handling the electrolyte. In the event at skin or eye contact the remedy is to wash with plenty of clean water (for 15 minutes) to dilute and remove the solution quickly. Speed is vital to prevent burn damage; and water, which is the best flushing agent, must be readily available. Neutralizing compounds (usually weak acids) cannot always be located easily, although they should be available in battery compartments.
Specific of electrolyte in a Ni-Cd cell is about 1.210 and this does not change with charge and discharge as in lead-acid cells. However, over a period of time the strength f. the solution will gradually drop and renewal is necessary at about a specific gravity of 1.170
Containers
The electrolyte slowly attacks glass and various other materials. Containers are therefore of welded sheet t which is then nickel plated or moulded in high-impact polystyrene casings are preferred when batteries are subject to shock and vibration. Hardwood crates are used to keep the cells separate from each 2t and from the support beneath. Separation is necessary cause the positive plate assembly is connected to the steel casing.
Thursday, June 10, 2010
Marine Engine Q & A- Electrical-Nickel Battery Discharging & charging action
Discharge Action.
During discharge the complicated but uncertain action at the positive plates (hydrated oxide of nickel) cause’s hydroxyl ions (OHˉ) to be introduced into the electrolyte. As the action progresses the nickel hydrate is changed to nickel hydroxide. .Simultaneously, hydroxyl ions (OHˉ) from the electrolyte form cadmium hydroxide with the cadmium of the negative plates. Effectively, the hydroxyl ions (OHˉ) move from one set of plates to the other, leaving the electrolyte unchanged. There is no significant change in specific gravity through the discharge/charge cycle and the state of charge be found sing a hydrometer
Charging
A direct current supply for charging is obtained from ac. mains, through the transformer and rectifier in the battery charger. The positive of the charging supply is connected to the positive at the cell, and negative to the negative terminal. Flow of current from the charging source reverses the discharge action. The reactions are complicated but can be summarized by the simplified equation:
Marine Engine Q & A- Electrical-Nickel-Cadmium Storage Batteries
Nickel-Cadmium Storage Batteries
The active materials of positive and negative plates In each cell of a charged nickel-cadmium battery (Fig 1.2) are nickel hydrate and cadmium, respectively. The chemicals are retained in the supporting structure of perforated metal plates and the design is such as to give maximum contact between active compounds and the electrolyte.
The strong alkaline electrolyte is a solution of potassium hydroxide in distilled water (with an addition of lithium). The ions produced in the formation of the potassium hydroxide solution (K+ and OHˉ) act as current carriers and take part in an ion transfer.
The active materials of positive and negative plates In each cell of a charged nickel-cadmium battery (Fig 1.2) are nickel hydrate and cadmium, respectively. The chemicals are retained in the supporting structure of perforated metal plates and the design is such as to give maximum contact between active compounds and the electrolyte.
Marine Engine Q & A- Electrical-Plate Construction,Electrolyte
Describe the plate construction of lead-acid battery.
Describe the eletrolyte reaction of lead-acid battery.
Plate Construction
A lead-acid battery is made up of a number of cells each with a nominal voltage of 2 volts Thus three cells separated by divisions ii common casing and connected in series make up a 6 volt battery, and six cells arranged in the same way make a 12 volt battery. Each cell has, say, seven positive and eight negative plates which are interleaved and arranged alternately positive and negative. Common practice is to have both end plates negative. Plates are prevented from touching by porous separators of insulating plastic; the design of the plates is such as to give the greatest possible surface area, adequate strength and good conductivity. The porous paste active material extends plate area to give maxi mum contact between active material and the electrolyte, and therefore good capacity. The oxide paste has little strength and is a poor conductor of so the deficiencies are made by a lead-antimony grid into which the taste is pressed.
Electrolyte
Sulphuric acid used to make .electrolyte for lead-acid batteries is, in its concentrated form. a non-conductor of electricity. In solution with water it becomes an electrolyte because of the break down of the H molecules into hydrogen (H+) ions and sulphate (SOˉ ˉ) ions as current carriers in the liquid.
Concentrated sulphuric acid has a great affinity for water and this, together with the heat evolved when they-come Into contact makes the production of electrolyte hazardous. A violent reaction results if water is added to concentrated sulphuric acid. Successful safe mixing is only possible if the acid is very slowly added to pure water while stirring .Normal the electrolyte is supplied ready for use in acid-resistant container.
Electrolyte is strongly corrosive and will damage the skin as well as materials such as paint wood, cloth, etc. on which it may spill it is recommended that electrolyte on the skin be removed by washing thoroughly (for 15 minutes) with water . Acid resisting paint must be used on battery room decks.
Describe the eletrolyte reaction of lead-acid battery.
Plate Construction
A lead-acid battery is made up of a number of cells each with a nominal voltage of 2 volts Thus three cells separated by divisions ii common casing and connected in series make up a 6 volt battery, and six cells arranged in the same way make a 12 volt battery. Each cell has, say, seven positive and eight negative plates which are interleaved and arranged alternately positive and negative. Common practice is to have both end plates negative. Plates are prevented from touching by porous separators of insulating plastic; the design of the plates is such as to give the greatest possible surface area, adequate strength and good conductivity. The porous paste active material extends plate area to give maxi mum contact between active material and the electrolyte, and therefore good capacity. The oxide paste has little strength and is a poor conductor of so the deficiencies are made by a lead-antimony grid into which the taste is pressed.
Electrolyte
Sulphuric acid used to make .electrolyte for lead-acid batteries is, in its concentrated form. a non-conductor of electricity. In solution with water it becomes an electrolyte because of the break down of the H molecules into hydrogen (H+) ions and sulphate (SOˉ ˉ) ions as current carriers in the liquid.
Concentrated sulphuric acid has a great affinity for water and this, together with the heat evolved when they-come Into contact makes the production of electrolyte hazardous. A violent reaction results if water is added to concentrated sulphuric acid. Successful safe mixing is only possible if the acid is very slowly added to pure water while stirring .Normal the electrolyte is supplied ready for use in acid-resistant container.
Electrolyte is strongly corrosive and will damage the skin as well as materials such as paint wood, cloth, etc. on which it may spill it is recommended that electrolyte on the skin be removed by washing thoroughly (for 15 minutes) with water . Acid resisting paint must be used on battery room decks.
Marine Engine Q & A- Electrical-Gas Emission,Topping up
Gas Emission
Towards the end of charging and during overcharge, the current wing into the cell causes a breakdown or electrolysis of water in electrolyte shown by bubbles at the surface. Both hydrogen and oxygen are evolved and released through cell vent caps into battery compartment. There is an explosion risk if hydrogen is allowed to accumulate (flammable range is 4% to 74% of hydrogen air). Thus regulations require good ventilation to remove gas and precautions against naked lights or sparks in enclosed battery compartments (see below)
Topping up
Batteries suffer water loss due to both gassing and evaporation, with consequent drop in liquid level There is no loss of sulphuric acid from the electrolyte (unless through spillage) checks are made to ensure that liquid level s above the top of the plates and distilled water is added as necessary. Overfilling will cause the electrolyte to bubble out of the vent.
Towards the end of charging and during overcharge, the current wing into the cell causes a breakdown or electrolysis of water in electrolyte shown by bubbles at the surface. Both hydrogen and oxygen are evolved and released through cell vent caps into battery compartment. There is an explosion risk if hydrogen is allowed to accumulate (flammable range is 4% to 74% of hydrogen air). Thus regulations require good ventilation to remove gas and precautions against naked lights or sparks in enclosed battery compartments (see below)
Topping up
Batteries suffer water loss due to both gassing and evaporation, with consequent drop in liquid level There is no loss of sulphuric acid from the electrolyte (unless through spillage) checks are made to ensure that liquid level s above the top of the plates and distilled water is added as necessary. Overfilling will cause the electrolyte to bubble out of the vent.
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