Part 38 (1/2)
The rates of discharge given here for the ”starting-ability” tests may be varied if experience with a particular make of battery shows some other rate to be better. The important thing is to use the same rate of discharge for the same make and type of battery at all times. In this way the repairman will soon be able to distinguish between good and bad batteries of a particular make and type.
Cadmium Tests may be made during the Starting Ability Discharge Tests.
See page 174.
”Cycling” Discharge Tests
New batteries, or rebuilt batteries which have had new plates installed, or sulphated batteries which will not ”come up” on charge, should be discharged when they have ”come-up,” as far as they will go.
In some cases it is necessary to charge and discharge them several times before they will be ready for service. This charging and discharging is often called ”cycling” the battery.
New batteries are generally ”cycled” at the factory before sending them out. The forming charge generally does not convert all the pastes into active material and the battery using plates which have been treated in the forming room is put through several discharges and charges after the battery is fully a.s.sembled. In service on a car, the battery is being ”cycled” constantly and there is generally an increase in capacity after a battery is put on a car. Positive plates naturally increase in capacity, sometimes up to the very clay when they fall to pieces, while negatives tend to lose capacity with age.
Batteries which are a.s.sembled in the service station, using new plates, generally require several cycles of charge and discharge before the specific gravity will rise to 1.280 before the positives will give 2.4-2.5 volts on a Cadmium test, before the negatives will give a reversed voltage reading of 0.175 to 0.20 volt on a Cadmium test, and before a satisfactory ”starting-ability” or ”breakdown” test can be made.
A battery which has been abused by failing to add water to replace evaporation, by allowing to remain in a partially or completely discharged condition for sometime, or which has been allowed to become sulphated in any other way, will generally require ”cycling” before it will ”come-up” to a serviceable condition.
The rates for a ”cycling” discharge should be such that the battery will be discharged during the daytime, the discharge being started in the morning, and the battery being put back oil the charging line in the evening in order that it may be charging during the night. The rate of discharge should be somewhat higher than the rate used when the plates are formed. Two or three amperes per positive plate in each cell will generally be satisfactory.
Discharge Apparatus
A simple discharge rheostat is shown in Fig. 180. The terminal on the end of the cable attached to the right hand terminal of the battery shown in the ill.u.s.tration is movable, and it may be clamped at any point along the coils of wire so as to give various currents. The wire should be greased lightly to prevent rusting.
[Fig. 180 Simple high rate discharge rheostat]
Another simple apparatus consists of a board on which are mounted six double contact automobile lamp sockets which are all connected in parallel. A pair of leads having test clips attached is brought out from the sockets for fastening to the battery terminals. Lamps of various candlepower may be turned into the sockets to obtain different currents.
Discharge tests are helpful in the case of a battery that has lost capacity. The battery is first fully charged, and is then discharged at the 5 hour rate. When the voltage of the battery has fallen to 1.7 volts per cell (measured while the battery is discharging) a Cadmium test is made to determine whether the positives or negatives are causing the lack of capacity. For further descriptions of the Cadmium Test see Page 174.
In reviving sulphated batteries, it is sometimes necessary to charge and discharge the battery several times to put the active material in a healthy condition.
Discharge tests at a high rate are very valuable in diagnosing the condition of a battery. A description of such tests will be found on Page 267. For making the heavy discharge tests a rheostat of the carbon plate type is suitable. With such a rheostat currents from 25 to more than 200 may be drawn from a six volt battery, and a smooth, even variation of a current may be obtained from the minimum to the maximum values. Such a rheostat is on the market and may be purchased complete with ammeter and leads for attaching to the battery.
PACKING BATTERIES FOR s.h.i.+PPING
Batteries which are s.h.i.+pped without electrolyte need merely have plenty of excelsior placed around them in a strong crate for protection from mechanical injury.
Batteries which are s.h.i.+pped filled with electrolyte must be protected from mechanical injury and must also be packed so that it is difficult to turn the crate upside down and thus allow the electrolyte to run out. A very popular crate has been the so-called ”dog-house,” with a gable roof such as is actually used on dog-houses. The idea of such a roof is that it is impossible to place the crate with the roof down, since it will tip over if this is done. However, if these crates are placed side by side, it is a very simple matter to put a second row of crates on top of them, turning the second row up-side-down, as shown in Fig. 181, and allowing the electrolyte to run out. The men who load freight or express-cars have often shown great skill and cunning in packing ”dog-house” crates in other ways so as to damage the batteries. Many have attained a high degree of perfection in breaking the crates.
[Fig. 181 ”Dog-house” crates for s.h.i.+pping batteries]
Some sort of a roof on a battery crate is required by law, the idea being to make it difficult to turn the crate up-side-down. Perhaps the best crate would be one with a flat top marked ”This Side Up,” but such a crate would not comply with the law.
[Fig. 182 Steps for construction of a crate for s.h.i.+pping battery]