See full version: How To Charge A Lead Acid Battery
If too low a charge voltage is applied, the current flow will essentially stop before the battery is fully charged. This allows some of the lead sulfate to remain on the electrodes, which will eventually reduce battery capacity. more
Power Sonic recommends you select a charger designed for the chemistry of your battery. This means we recommend using a sealed lead acid battery charger, like the the A-C series of SLA chargers from Power Sonic, when charging a sealed lead acid battery.
The constant voltage charge method applies a constant voltage to the battery and limits the initial charge current. It is necessary to set the charge voltage according to specified charge and temperature characteristics. Inaccurate voltage settings can cause either over-charge or under-charge. This charging method can be used for both cyclic and standby applications.
When using a taper current battery charger the charger time should be limited or a charging cut-off circuit needs to be incorporated to prevent over-charge.
The BULK stage in a 24 volt charger involves about 80% of the recharge, wherein the charger current is held constant (in a constant current charger), and voltage increases. The properly sized charger will give the battery as much current as it will accept up to charger capacity (25% of battery capacity in amp hours), and not raise a wet battery over 125� F, or an AGM or GEL (valve regulated) battery over 100� F. The target voltage for a 24 volt charger for AGM or some flooded batteries is 2.4 to 2.45 volts per cell, which is 28.8 to 29.4 volts. more
24 volt charger technology has kept pace with the technology revolution, and so current battery charging philosophy uses 3 stage (or 2 or 4 stage) microprocessor regulated charging profiles. These are the "smart chargers", and quality units generally are not found in discount stores. The three stages or steps in lead acid battery charging are bulk, absorption, and float (or sometimes complete shut off in some cases). Qualification, or equalization are sometimes considered another stage, usually for promotional purposes. A 2 stage unit will have the bulk and float stages. It is important to use battery manufacturer's recommendations on charging procedures and voltages, or a quality microprocessor controlled charger to maintain battery capacity and service life.
True Gel batteries generally require a specific charge profile, and a gel specific or gel selectable or gel suitable charger is called for. The peak charging voltage for Gel batteries is 2.3 to 2.36 volts per cell, and for a 24 volt charger this works out to 27.6 to 28.3 volts, which is lower than a wet or AGM type battery needs for a full charge. Exceeding this voltage in a Gel battery can cause bubbles in the electrolyte gel, and permanent damage, as the bubbles in the gel do not dissipate when the over voltage condition ceases.
The ABSORPTION stage (the remaining 20%, approximately) in the AGM/flooded 24 volt charger has the charger holding at the absorption voltage (between 28.8 VDC and 29.4 VDC, depending on charger set points) and decreasing the current until the battery pack is fully charged. If the battery won't hold a charge, or the current does not drop after the expected recharge time, the battery pack may have some permanent sulphation.
A circuit that is set for the maximum allowable charge voltage, but has a current limit to control the initial absorption current can produce a very nice charger. This type of charger can both charge at a reasonable rate and maintain the battery at full charge without damage. Not all constant voltage chargers are made equal, however, because the maximum voltage is a function of temperature. A temperature compensated charger is a little more expensive, and should be used where the temperature varies significantly from room temperature and the battery is on float permanently. The large chargers at An example of a switching type taper charger is here are constant voltage chargers. here
Sealed lead acid batteries are higher in charge efficiency, depending on the bulk charge voltage it can be higher than 95%.
Big battery applications such as fork lifts, floats, and golf carts have traditionally used what is called rectifiers to charge their batteries because of the relatively low price for large power levels. The "rectifier" consists of a transformer and diode bridge array and possibly some control or readout electronics. These work well, but the voltage might not be well regulated, which is made up for by using flooded batteries where the water can be topped off. These chargers are not appropriate for sealed lead acid batteries because their water cannot be replaced. And modern switchmode technology has made it possible to make inexpensive well regulated lead acid battery chargers such as this 8000 watt 48V charger.
Any multistage charger that has a "float" mode can be used to maintain batteries during the 'off-season.' Particularly useful are the small, inexpensive switchmode chargers that consume very little excess power , or the small low-power chargers that can automatically desulfate lead acid batteries.
These are the absolute cheapest chargers around. They consist of a wall mount transformer and a diode. The transformer is designed to deliver 13 to 14 volts over a reasonable current range. The biggest problem with this approach is that when the current tapers off, the voltage raises to 15, 16, 17, even 18 volts. At these high voltages electrolysis of the water in the battery starts in. These must not be left to trickle or float charge a battery, they must be disconnected when the battery is fully charged. This is not a problem with flooded batteries as long as you check the water periodically and refresh it. Sealed lead acid batteries can recycle the generated gasses as long as they are being overcharged at less than C/3. However, leaving the battery to be overcharged even at C/10 will corrode the plates if left on for weeks at a time. more
Float Voltage: 2.25 VPC
- A 4500-watt Solar Array Configured to charge a 48-volt battery bank. This array is connected to an 80 Amp charge controller that will peak at 80 Amps of solar power. This value will be de-rated by 20% due to typical, solar array in-efficiencies caused by shading, heat, improper angle and soiling. (ex. adjusted to 65 Amps) here
If you do not have a battery temperature sensor (BTS) installed, then you must test and actively adjust the charging voltages based on the temperatures of the batteries, not the ambient temperatures of the battery bank.
In this example, the solar array is undersized for adequate charging. The charge source should be capable of a current output between 10% to 20% of the C/20 rate of the battery bank. A rate of 10% will require 4.2 hours of Absorption charge which is considered a typical daily charge time using a PV array. Undersizing the system and charging at a rate lower than 10% will result in undercharging due to limited charge time (solar). [links]