What are Equalize, boost and fast charging?

How are equalize, boost and fast charge charging different?
Each of these terms describes the same function of the charger where the charger temporarily elevates the batterys voltage above the float level. There are different uses for elevated charge voltage, as shown below: http://www.everexceed.com/
Commonly understood meaning of the term
Equalize Periodic topping up of battery capacity, and correct cell capacity differences
Boost Can refer to equalize, fast charge, and sometimes both
Fast charge Faster recharge of a discharged battery

What does equalize charging do, and why is it needed?
All batteries, even those assembled into unitized blocks, are all built of individual battery cells connected in series to obtain the required DC voltage. Like all manufactured products, there is variation between the capacities of each cell in the battery. As the battery ages this variation increases. Since the battery is a chain of cells that is only as strong as the weakest link some scheme is required to ensure that all cells stay at peak capacity.
A scheme called equalizing is commonly used in both lead-acid and nickel cadmium batteries. Equalizing temporarily elevates the charging voltage of the entire battery string above the normal float voltage. The elevated charging voltage allows all cells, including the weak ones, to accept more current from the charger than they would at float voltage. A consequence of the elevated equalize voltage is that all cells in the battery are overcharged. This is acceptable for short periods provided the battery has sufficient electrolyte.
Overcharging greatly increases the rate at which the water in battery electrolyte is electrolyzed into oxygen and hydrogen gas. Since low electrolyte level will permanently damage the battery it is important to limit when, and for how long, the battery is charged at the equalize voltage.

What is fast charging?
Batteries, like all electrical conductors, suffer from resistance in their conductive metals. Ohms law says that resistance increases in proportion to current flow through the battery (or any other imperfect conductor). This means that the more amperes of charge we attempt to apply to the battery the more will be lost due to internal heating.
Fast charging temporarily increases the chargers output voltage to compensate for the batterys internal resistance. This allows the battery to continue accepting maximum current from the charger for a longer time instead of reducing its charge acceptance early as it would if charged at normal float voltage.

What is the correct charging voltage?
The value of both float and equalize/boost/high rate voltages is determined by the battery manufacturer, and depends on the chemistry and construction of the battery. Deviating from the recommended values, except where needed to adjust for temperature, will under or overcharge the battery both of which will reduce the batterys life and performance.

How do you know when the charger should operate in float or equalize mode?
Regardless of the intended purpose of increasing the chargers voltage there needs to be a way to start and end charging at voltage higher than float.
The most common control methods are shown below.
Control method: Manual switch
Advantage: Simple, cheap
Disadvantage: High risk of forgetting unit is operating at elevated charging voltage
Comment: Not recommended
Control method: Automatically initiated timer
Advantage: Suited for remote sites where users do not visit frequently
Disadvantage: Time must be pre-programmed.
Comment: The correct pre-programmed time cannot be predicted since depth of discharge is likely to vary
Control method: Automatic initiation with battery-determined end
Advantage: Termination of elevated charge voltage is based on battery needs, not a program
Disadvantage: High continuous current can trick system into staying at elevated voltage too long
Comment: Functions like an automatically initiated timer, but can end discharge earlier if batterys state of charge is satisfactory
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