During use, a battery alternates between two states, fully charged and fully discharged. When you test a battery and determine that it requires charging, you will have to decide how it is to be recharged.
While an engine is running, the battery charge is maintained by the charging system. Occasionally, however, the battery charge may wear down and if not attended to, the battery will not have enough power to start the engine. When a battery ’s state of charge is low, it should be recharged. Recharging can be done on the battery either while it is in the vehicle or after is has been removed. There are a number of different battery chargers classified as constant current or constant voltage.
Constant current chargers
A constant current charger supplies a constant or set amount of current to the battery. The recommended charging rate is 1 amp per positive battery plate per cell. For example, if a battery has five positive plates per cell, it should be charged at 5 amps. most batteries which are slow charged with a constant current charger will take 5 to 6 amps.
Constant voltage chargers
A constant voltage charger supplies the battery with a constant voltage during the charging period, for example,15 volts for a 12 volt battery. This charger will charge the battery at a fairly high amperage when the battery is low and then as the battery builds up charge, the amperage tapers off almost to nothing as the battery becomes fully charged. Constant voltage chargers are much more common than constant current chargers.
Charging conventional batteries
Time is usually the main factor when you decide whether to fast charge or slow charge a battery. Obviously, it is better to slow charge a battery because you get a more thorough charging job. However, you do not always have the time (24 to 48 hours) to do a slow charge and in such cases fast charges have to be done.
Constant current slow chargers
A slow charger can be either constant current or constant voltage (constant voltage is more common). Chargers have printed on them the maximum amount of voltage that they will produce. For example, a 60 volt charger could be used for five 12 volt batteries (total 60 volts)or ten 6 volt batteries (total 60 volts).
The term slow charging refers to a charge rate of 10 Amps or less. When there are a number of batteries of different sizes on the charger, average out the charge rate. On some of the new chargers, you do not have to bother counting or averaging out the new positive plates.
These chargers have a yellow, green and red band on the charge rate indicator and it is recommended the control be set in the green range.
To connect a constant current charger, start with the black lead (negative) from the charger and connect it to the positive post of the last battery. Now, using good jumpers, connect the batteries, positive to negative to complete the series circuit.
Recheck all the connections by turning the connections slightly on the posts. Finally, turn the charger on and adjust it to the correct charge rate.
The state of charge of a battery being charged should be checked with a hydrometer twice a day, if possible. The total charging time will vary depending on the strength of the charge to begin with, but at the end of 48 hours batteries should be fully charged.
If a battery becomes fully charged (its specific gravity is 1.275 or over) before 48 hours are up, remove it.
Constant voltage slow chargers
Constant voltage chargers are connected to batteries in parallel. The maximum number of batteries a charger can handle will be marked on the charger. The voltage control is set at a specified voltage, such as 15 volts for a 12 volt battery. The charge rate is automatically sensed by the charger.
The charge rate will be high when the discharged battery is first connected to the charger and will gradually taper off as the battery becomes fully charged. When connecting batteries in parallel to a constant voltage charger, from the charger and connect it to the negative (-)post of the first battery. Now using good jumper cables connect the batteries negative to negative and positive to positive. As with a constant current charger, check the specific gravity of the charging batteries twice a day and remove the batteries when they are fully charged.
Fast chargers will give a battery a high charge for a short period of time, usually no more than one hour. They are portable in contrast to slow chargers that are usually mounted to a wall or sit in a permanent position on a bench. Portable fast chargers can charge a battery while it is still in the machine. Generally, only one battery at a time is
charged on a fast charger. Many modern fast chargers have a capacity to slow charge a battery as well.
Precautions when fast charging
Whenever a battery is charged, especially fast charged, never allow the electrolyte to exceed 51 °C (125 °F). Watch the color of the electrolyte when fast charging batteries. As a battery ages the electrolyte will become discolored by sediment.
During a fast charge the sediment is stirred up and could get trapped between the plates, causing a short. Check the color of the electrolyte during charging with the hydrometer and, if sediment begins to appear, reduce the charging rate.
Correct battery charging practice
Before connecting conventional batteries to a charger make sure that the battery tops are clean and the electrolyte is up to the correct level.
All chargers, slow or fast, need 110 V alternating current supply. Always make sure the charger is turned off before connecting it to a battery.
When connecting any charger, observe the correct polarity. Always be sure to connect negative to negative and positive to positive. Most chargers are polarity protected.
Check the charger voltage settings before turning it on. On a constant voltage slow charger set the voltage to match the number of volts in the batteries you are charging. On a constant current charger, set the voltage for 6 or 12 V depending on which battery you are charging.