# Understanding Battery Chraging

Discussion in 'Renewable Energy' started by R.G, May 14, 2014.

1. ### R.GNew Member

Joined:
May 14, 2014
Messages:
1
Likes:
0
We(University) bought a power system with a Wind Turbine ,Ac2DC Converter ,Charge Controller and a Battery ,
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?

2. ### NorthGuyWell-Known Member

Joined:
Sep 8, 2013
Messages:
1,218
Likes:
206
Location:
Bulk. The controller pushes as much current into the battery as it can. Battery voltage rises, but not dramatically because battery "takes" charge.

1. It is up to the controller.
2. No

Absorption. Battery doesn't take charge as easily and its voltage wants to rise, so the controller limits current to make sure the battery voltage doesn't go above the set value.

1. Battery voltage is kept constant. It is kept constant by limiting current into the battery. Wind controller simply directs the excess current to a diversion load.

2. Battery gets more and more charged. As it approaches the full charge, it can take less and less current. So, the controller has to decrease the current to maintain the same voltage.

• Dislike x 1
3. ### Traveller30New Member

Joined:
Jul 11, 2009
Messages:
5
Likes:
0
NorthGuy , thank you for the fast reply
you wrote " Battery gets more and more charged. As it approaches the full charge, it can take less and less current. So, the controller has to decrease the current to maintain the same voltage."
1: Why it can take less and less current? I understand that's the battery is more charged ,does it mean its resistance is rising? if the voltage of the battery is constant , the voltage of the Controller is constant, why the current between them changes? I guess I need a battery model , does it behave like a resistor ,capacitor or coil , some superposition of them?

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### NorthGuyWell-Known Member

Joined:
Sep 8, 2013
Messages:
1,218
Likes:
206
Location:

Imagine a capacitor. All the current that it takes is converted to voltage. It cannot take any current without its voltage going up.

Now imagine that the capacitor is submerged into an encironment where a chemical reaction takes place taking off the charge from the plates. You push current into it, but it's immediately consumed by the chemical reaction. The battery takes current. The voltage doesn't rise.

It is only so much of chemicals in the battery, so as it runs out of chemicals, the chemical reaction slows down more and more, and therefore the battery strarts behaving more as a capicitor.

Controller is a complex device which is capable of changing voltages and currents to meet its goals.

6. ### nsaspookWell-Known Member

Joined:
Mar 24, 2010
Messages:
1,141
Likes:
219
Location:
Fairview, Or
I really don't like to compare batteries to capacitors because they are truly different in the method of energy storage. It's usually better to think of a battery as a generator with a energy source that can be replenished (electrical to chemical to electrical) instead of recharged with electricity like a capacitor.

The plates of the battery readily accept surface charge which is about 80% of total charge in a lead-acid battery (this is bulk). Once the surface charge has all been converted the Redox reaction moves below the surface to react with more of the plates(Absorption). To do this it has to overcome the equilibrium voltage of the cells current conduction to continue the chemical reaction so we increase the voltage but limit the amount of current because the energy to required to overcome the equilibrium causes the reaction to heat and decompose the water into the gases.

7. ### 4pyrosWell-Known MemberMost Helpful Member

Joined:
Oct 22, 2010
Messages:
4,368
Likes:
282
Location:
Pennsylvania, USA
8. ### Traveller30New Member

Joined:
Jul 11, 2009
Messages:
5
Likes:
0
again , thank you all for you help

Joined:
Jun 3, 2010
Messages:
2,611
Likes:
129
Location:
Caribbean
10. ### RCinFLAWell-Known Member

Joined:
Jul 23, 2009
Messages:
1,065
Likes:
31
Location:
FLA, USA
Bulk phase - constant current, limited to size/type of battery to avoid damage to battery due to excessive charge rate. Typical current level held to less then 15-20% of AH rating in amps.

Absorb phase - held at constant absorb voltage (typ. 14.2-14.5v) until current drops off to some determined value, typically 3 to 10% of bulk phase current level.

Float - maintain trickle charge on battery. typically 13.2-13.8v for six lead acid cells in series.

Equalization - (not to be done on sealed / maintenance free lead acid batteries) - controlled overcharge, typically 15.0-15.5v for 20 minutes to couple of hours. Breaks up soft lead sulfate and returns blocked plate sites. Can bring back specific gravity balance between cells. Is stressful on battery and should not be done too often. Cracks water in electrolyte (lots of electrolyte bubbling) to oxygen and hydrogen which needs to replace water consumed. Be aware of released hydrogen/oxygen gas during process in poorly ventilated area with possible ignition source.

Electrolyte begins to crack more water above about 14.2v so some gassing happens as battery approaches absorb voltage level during normal charging process.