BATTERY CHARGING ANS MAINTANCE OF LEAD-ACID BATTERIES.
When suitable mains and Power Packs are available, they should be used as the source of power, but when these are not available then very satisfactory results can be obtained by using a 6 Volt accumulator and a vibrator pack, but only if the battery is fully charged and in good condition. It is therefore essential that the operator who has to rely on batteries should pay special attention to Battery Charging and Maintenance.
A run down battery should be recharged by means of proper charging plant at the rate specified by the makers of the battery until cells are gassing freely and the voltage and specific gravity of the acid in each cell have remained constant for three hours. Trickle charging, or any form of prolonged charging at very low rates, is not recommended. It will impair the performance, reduce the life of the cells and should only be resorted to in an emergency.
That the battery should be fully charged is of first importance consequently, especially when in the field, any means to that end is acceptable and frequently only one method is available.
Electricity for battery charging may be obtained by three methods:
1. The Thermo Couple Charging
This consists of 350 junctions of Constantan and Chromel built into fireclay brazier. With a good brushwood or coal fire burning, a 6 Volt may be chatged at about 1 Amp. This charger is heavy (23 lbs) and is only useful at base or semi-permannent camps.
2. Mains Charges.
These may be divided broadly into three types:
a. Those suitable for DC Mains only.
b. Those suitable for either AC or DC.
c. Those suitable for use on AC mains only.
Firstly examine the electric meter or electrical apparatus in use to ascertain whether the mains are AC or DC and their voltage.
a. Assuming they are DC and 200 to 250 Volts, battery charging is simple.
Connect up the circuit shown below.
If the mains are 200 Volts and the lamp is 100 Watts, the charging current will be 100/200=½ Amp. If a 1000 Watt Electric fire is substituted foor the 100 Watt lamp, then the current will be 1000/200=5 Amps.
It is important that the polarity of the mains should be known and connected correctly. If there is any doubt about this, connect up the circuit shown above using a lamp, but instead of attaching the wires to the battery, hold them an inch or two apart in a glass of water. Bubbles will appear at the negative lead. This wire should be connected to the negative terminal of the battery and the corresponding mains plug marked for future reference.
b. Some chargers may be used on either AC or DC mains and in the absence of switches or moveable plugs it is probably that the circuit will be as shown below.
If the mains are AC, the lamp drops the voltage and the rectifier acts as a rectifier, but if they are DC, the rectifier simply acts as a small additional resistance but only if the mains are connected with the correct polarity, otherwise it will act as a considerable resistance and may be damaged
If DC, test the mains for polarity as before.
c. With chargers for AC Mains only, there is no question of the polarity of the mains connection, but the tappings or switches should be set to the voltage most nearly corresponding to the mains voltage and the accumulator connected, making sure that the positive (+VE) of the battery should be connected to the positive (+VE) terminal of the charger. Similarly, the negative (-VE) of the battery should be connected to the negative of the charger.
If a charger ceases to function, check any fuses on the charger or mains before suspecting other breakdown.
3. Generators. (Coils moving in a magnetic field)
A large range of these generators is available, the chief difference being in the method of driving the armature.
In this case drive is by means of a geared propellor attached to the generator and the whole supported on a 10 ft. steel lattice mast, total weight 100 lbs.
b. Hand Generators.
There are several varieties of hand driven generators, some fitted on a tripod and others with clamps for attaching to a table of shelf. Their weight vary from about 5 lbs to 11 lbs and when turned at 80rpm, charge a 6 Volt battery 2.5 to 3 Amps.
c. Pedal Generators and Cycle Adaptors.
Again there are variations in the method of drive. In the case of the Cycle Adaptor, the generator, together with a stand, is fitted to a standard cycle; which when pedalled at normal cycling speeds, will charge a 6 Volt battery at 4 to 5 Amps.
Similarly, a Pedal Generator is a stand with saddle, generators and pedals which, when pedalled as above, will charge a 6 Volt battery at 3 to 5 Amps.
1. Always attach the positive (+VE) lead from the generator to the positive (+VE) terminal of the accumulator and the negative (-VE) to the negative (-VE) terminal.
2. When so attached, unless the battery is very low indeed, the battery will drive the generator will turn the pedals. This discharging the battery still further, so pedalling should be gin at once in order to tun the generator at a greater rate.
Disconnect the battery as soon as pedalling stops.
d. Petrol driven Generators.
Two types of small petrol driven generators are available. That known as the RB-8 is a small two stroke engine, consuming 2/3 pint of petrol per hour, attached to a baseboard 28" x 15" and coupled to the generator. The total weight is 82 lbs. A 12 Volt battery (or two 6 Volt batteries instead) is charged at 6 to 7 Amps.
The RAF 288 Watt JAP 4 stroke petrol electric set frequently met with, is designed to generate over a range of 14.32 Volts for charging a12V, 18V and 24 Volt batteries. The normal charging rate is 9 Amps and the maximum (for ½ hour) is 15 Amps.
Size: 2' 2½ x 10" x 1' 7".
Weight: 90 lbs approx.
e. Steam Powered Generator.
This consists of a boiler suspended in a brazier (weight 48 lbs) and connected with a flexible tubing to a small twin cilinder steam engine directly coupled to a generator (weight 22 lbs). With a steam pressure of 30 to 35 lbs per sq. inch and a consumption of half a gallon of water and 15 to 20 lbs of wood per hour, a 6 Volt accumulator may be charged at 4 Amps.
THE CARE OF BATTERIES.
STORAGE PRIOR TO USE.
1. The batteries are supplied in an unfilled uncharged condition. Any liquid observed in the cells prior to filling in and first charge is water condensate from wet separators. This will have no adverse effect on the operation of the cells..
2. The store room must be dry and should be kept as cool as possible. The cells should preferably be stored in the dark, but, in any case, the must be protected from the direct rays of the sun.
3. The cells are suitable for storage unfilled in temperate climates for 12 months after date of manufacture (6 months in case of storage in the tropics). Longer periods up to twice the above mentioned will not necessarily be harmful, but may cause trouble to develop in odd cells.
OPERATING INTO SERVICE.
4. Fill each cell with cool "accumulator" sulphuric acid of 1:280 specific gravity, up to the red "level line" marked on the box.
5. Allow the cells to stand for about 12 hours (at least 8 hours and not more than 24 hours). Restore the level by adding further acid of 1:280 specific gravity.
6. Charge at the specific rate (2 amperes fot type 3-SAF-15, ¾ ampere for type MFA-13), for not less than 48 hours. This may be given continuously or in stages, but in any case continue the charge until the voltage and the specific gravity of the acid in each cell has remained constant for 3 hours. The final specific gravity obtained will be in the neighbourhood of 1.250. If possible, do not allow the temperatures of the acid in the cells to exceed 100 F. A reduction in temperature may be obtained by interrupting the charge or by reducing the charging current. In the latter event the charging time must be proportionately increased. In tropical climates it may be helpful to immerse the cells up to within 1" 0r 2" of the top in a water-bath during the first charge, but careful preparations against shock and fire risk will be necessary, especially if the voltage of the charging circuit is above, say, 50 Volts.
7. IMPORTANT. At the end of the first charge poor out the electrolyte and refill immediately with fresh acid of1,280 specific gravity. The cells are then ready for service.
OPERATION IN SERVICE.
8. When to recharge. The cells should be recharged:
a. immediately prior to each operational discharge.
b. Whenever the specific gravity has fallen to 1.150 or the voltage has fallen on load to 1.80 Volts. If the cells have been discharged to a specific gravity below 1.150 it is essential to give them a recharge IMMEDIATELY.
c. In any case, even if the cells have been standing idle, they must be recharged at least every month in temperate climates or every two weeks in tropical climates.
9. How to recharge. Whilst on charge, the cells should stand on a dry bench or floor of some insulating material. A wooden bench covered by glass sheets makes a very suitable arrangement. Charge at the specified rate (2 amperes for type 3-SAF-15, ¼ ampere for type MFA-13) until the cells are gassing freely and the voltage and specific gravity of the acid in each cell have remained constant for 3 hours. the final specific gravity should be in the neighbourhood of 1.280. The time required for recharge will depend on the length of time and the amount of discharge taken out since the previous recharge. The cell vent plugs should be left in position during the recharge. Endeavour to keep the temperature of the acid in the cells below 100°F during charging. In this connection, it will help to interrupt the charge occasionally or to reduce the charging rate, to say, half the specified rate. In tropical climates it will help considerably if charges are only given during the night-time.
10. Topping up. maintain the level of acid at the red line marked on the box by the addition of distilled water as required. The best time to add the water is just before commencing a recharge. Do not allow the tops of the plates to become exposed to the air, otherwise they will deteriorate. Do not overfill above the red line, as this will lead to spillage. If distilled water is not obtainable, use clean rainwater which has been collected and stored without coming into contact with any metal (other than lead), Alternatively use clean melted snow. If in emergency, impure water has to be used (such as river water or chlorinated drinking water) change the acid as soon as possible afterwards in the manner described in paragraph 13. Never add acid to the cells except to compensate for spillage.
11. Cleanliness, etc. Keep the cells clean and the filling plugs and connections tight. Keep the terminals lightly smeard with pure vaseline or petroleum jelly, so as to prevent corrosion.
12. Safety. Never bring a flame or spark near the cells at any time, but particularly during or shortly after the recharge.
13. Changing Acid. Once every 6 months in temperate climates, or once every three months in tropical climates, give the cells a full recharge as described in paragraph 9, and then pour out the existing acid. Refill the cells immediately with fresh acid of 1.280 specific gravity. Never change the acid without first giving the cells a full recharge.
14. Idle Batteries. If the batteries are standing idle, then once per month in temperate climates or once in every two weeks in tropical climates, they must be topped-up as described in paragraph 10, and then recharged as described in paragraph 9. Batteries which are standing idle should be disconnected from all external apparatus.
15. Trickle Charging. Continuous trickle charging or any form of prolonged charging at very low rates, is not recommended. It will impair the performance and reduce the life of the cells.
16. Frothing. If cells are found to froth on charge, this may be stopped temporarily by dropping a small pinch of dry soap into the cells. A rather more lasting care may be effected by changing the acid as described in paragraph 13.
17. Special Precautions in Tropical Climates. In tropical climates pay special attention to the following points:
a. Cells which are being first-charged may with advantage be immersed in a water bath (see paragraph 6).
b. Topping-up will be required more frequently (see paragraph 10).
c. Charge the cells at least every two weeks, even if they are not in regular use (see paragraph 8).
d. pay special attention to the temperature of the acid during recharge (see paragraph 9).
e. Change the acid regularly every three months (see paragraph 13).
f. Keep the cells shielded from the direct rays of the sun.
g. It is advantageous to work the cells in 1.250 specific gravity acid instead of 1.280, but it must be remenbered that this will reduce the available capacity by about 10%.
18. Special Precautions in Very Cold Climates. In very cold climates some reduction in performance must be expected. Pay special attention to the following points:
a. When putting new batteries into service, the temperature of the charging room, and also of the filling acid, should preferably not be lower than 32°F (0°C).
b. Top-up with water, only when the cells are gassing towards the end of charge, and add not more than a teaspoonful of water at a time.
c. Recharge the cells frequently so that they are never more than partially discharged. Take care never to discharge the cells to a greater output than the following:
If the above outputs are accidentally exceeded, it is essential to recharge the cells immediately. If these precautions are not taken, the acid in the cells may freeze, in which case they will be ruined.