Questions about Battery charging mechnism

Hi
I need some help in understanding the basics of battery charging. I read about the three common stages: Bulk Charging, Absorption Stage and Float Stage, but I can't understand exactly what the controller does and how can it do it?


Let me explain my problem:


Bulk Charging:


"During the Bulk phase of the charge cycle, the voltage gradually rises to the Bulk level (usually 14.4v volts) while the batteries draw maximum current. When Bulk level voltage is reached the absorption stage begins"

1.
Does it mean that the controller voltage is gradually rising so it always will be above battery voltage, while the battery voltage is rising due to the current from difference on voltage (controller-battery)?


2.
Can the current to the battery can be calculated by Ohm's law: (Vcontroller-Vbattery)/Battery Resistance?



Absorption :



"During this phase the voltage is maintained at Bulk voltage level for a specified time (usually an hour) while the current gradually tapers off as the batteries charge up"

1.
The controller voltage is constant, or the battery voltage is kept constant? If it is the battery voltage, how can you keep constant voltage of a battery, if flow of current is into the battery, that means increasing voltage...


2.
Why does the current decrease with time if the Battery Voltage is being set constant? Does the resistance of the battery increase when it's more charged?

that's nice thread, i am also interested in to get answer

Battery charging can be of Simple Charging Mode, Trickle Mode (which I think is absorption mode) and then there is cut of stage when chargers stops charging the battery.
1. Battery is charged with the potential difference between controller and the battery voltage. Most of the time, the charger voltage is foxed about 17 to 18 volts for 12 volts battery. You are right that most of the chargers enter in trickle mode when reach at certain voltage level (approx. 12.5 volts)

The current flow should vary according to the voltage differential.

All batteries have internal resistance. You need to read the chemical composition of battery, lead acid, dry, lion, NiCd etc.

I think that might help you a bit

Bulk charging is limited by battery's thermal rise and tendency to outgas, but it is always Constant Current(CC) and usually rated by values such as C/10, C, or 10C which is the A-hr Capacity in 1 hr.

When V+ rises to limit such as 14.4V, current drops slowly, so now it is in Constant Voltage mode (CV) or phase 2.

When current drops below a certain threshold such as a few hundred mA, it is said to be near full capacity.

Then regulator switches to a lower reference voltage such as 13.8V for float voltage or phase 3 with longest life expectancy and current should be near zero if no leakage.

Good reply by SunnySkyguy....

ok ,got it
thank you for your help