Why do battery charger need float charging process

[forever074]

I have searched for battery charger. It used boost charging and float charging process. But I think boost charging process is enough.First, Battery was charged with 0.1C of Battery. When battery voltage equal boost voltage, the charging current decrease. When charging current equal Imin(full capacity) , charger switch off. So why charger need float process?
Could you explain this for me?

 

[shumifan50]

This sounds like a lithium battery.
Look here for a brief explanation:
Charging a Lithium battery

If it is a Lithium battery, you should also be aware that if anything goes wrong they can catch fire, which is why you get charging bags which are fireproof. Or place it in a place where a fire will not be a problem if it happens. This is especially true for the LiPos used for RC models where it is easy to get the settings wrong for the variety of available batteries.

Edit: Only just noticed that you charge at 0.1C which is very low for lithium batts, so maybe it is something different. LiPos only charge at 0.1C for the last phase, the rest of the time is normally 1C but can be as high as 20C for some batteries. Several charge controllers are available e.g. TP4056 fir lithium batts.


google is your friend

 

[Arouse1973]

You must not float charge li-ion batteries. Float charge is normally for LA or NIMH batteries. And is designed to prevent self discharge.
Adam

 

[(*steve*)]

You must not float charge li-ion batteries. Float charge is normally for LA or NIMH batteries. And is designed to prevent self discharge.
Adam

There's an interesting issue here. What happens when you have two of these batteries in parallel? Is that not similar to having them on a float charge?

The difference is that no current is (or should be) flowing in this case.

If you "float" charge with a voltage that causes zero current to flow, you're OK

Essentially that's the same thing as saying "don't float charge" because you normally terminate the last stage of charging when the current falls to a particular low value as distinct from zero.

 

[forever074]

Edit: Only just noticed that you charge at 0.1C which is very low for lithium batts, so maybe it is something different. LiPos only charge at 0.1C for the last phase, the rest of the time is normally 1C but can be as high as 20C for some batteries. Several charge controllers are available e.g. TP4056 fir lithium batts.
google is your friend

I mean Lead Acid Battery. It is recommended to charge at 0.1C.

 

[forever074]

You must not float charge li-ion batteries. Float charge is normally for LA or NIMH batteries. And is designed to prevent self discharge.
Adam

So if it is Lead Acid Battery, after boost charging process, is its capacity is fully.? Or need float charging process to make its capacity fully.

 

[Arouse1973]

You have fast charge, Trickle charge and float charge. The battery will be fully charged after the correct amount of time after trickle charge or some people call it topping off.

Constant current charge for 6 to 8 hours and trickle charge for the remaining 6 to 8 hours. As I mentioned float charge is not used to finish charging. it is used to replace what is loss through self discharge.

FYI
Li-ion are similar but you terminate the charge after the current is about 3% of the maximum recommended charging current. If you don't then plating occurs inside the battery which can cause in worse case damage to the battery and possible fire.

When you connect two lithium cells in parallel they have to be both discharged. Then the small variation between the cells will balance out after a short while and no current should flow between cells. This is ok because the cells are in a discharged state and can readily accept a charge anyway.

Thanks
Adam

 

[Kiwi]

This should answer your questions on charging lead acid batteries.

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

[forever074]

This should answer your questions on charging lead acid batteries.

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Float charge compensates for the loss caused by self-discharge. I understand it.
But in this article, it say "The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation" Does it mean If Battery is not full charged frequently, it will loss ability to be full charged later( its capacity decrease) ???

 

[shumifan50]

When you connect two lithium cells in parallel they have to be both discharged

They have to be at the same State of Charge(SOC), which could be partially discharged as well. In any event anything more than 1S serial packs should be charged with a balancing charger and the associated cable. It is not recommended to ever charge Lithium batteries in parallel, at least it will reduce their life, at most it could cause a fire, depending on SOC differences between the cells. Bear in mind that most cells are rated at 15C or more and that the current during inter-cell balancing can be huge, well above the rated/recommended current per cell, unless a balancing charger and cable is used. In the case of parallel cells balancing is not possible as the cells interact independently.
In any event, unless your battery or battery pack specifically state otherwise, they shoud always be charged at 1C, meaning the charge time will always be around 1 hour for discharged cells(around 3V). When around 4.2V is reached the charging should be reduced to 0.1C. Single chip charge controllers are available e.g. TP4026 and one from Microchip(cant remember the part number).

I never knew lead-acid batteries had special charging requirements, so I am pleased to have learned about that. I will now be a lot more dubious about the battery chargers sold by car spares shops as 'universal' when the AH rating differences can be huge, especially between motorcycle and car batteries - I have just been lucky that I have always used special m/cycle battery chargers for my bikes.

@forever074:
Yes lead-acid batteries should be kept fully charged at all times while watching the acid level. On the other hand Lithium batteries should be charged to around 3,8V when stored for extended periods of time.

 

[jpanhalt]

<snip>If deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation"

A fully charged lead-acid battery has two electrodes. One is pure lead (Pb), and the other is lead oxide [Pb(IV)O2], which is also called lead dioxide.. The electrodes are submersed in an electrolyte made of diluted sulfuric acid.

As the battery discharges, the lead electrode gives up electrons, which is called oxidation, to give Pb(II); the Pb(IV) electrode accepts electrons and the Pb(IV) is reduced to Pb(II). The Pb(II) forms sulfates, that is, Pb(II)SO4. When the battery is completely discharged, it will theoretically have just two electrodes of Pb(II)SO4 in water*.

Recharging the battery reverses that process. It regenerate the Pb(IV)O2 and Pb electrodes and produces sulfuric acid. That's the theory.

In reality, lead sulfate does not completely return to its original states. It effectively ages, becomes stable, and cannot be returned to its prior state of Pb or Pb(IV)O2. It forms a crystalline precipitate that insulates and or flakes off of the electrodes. That state is called "sulfation." For most practical purposes, sulfation is irreversible without disassembling and reprocessing the battery. The more sulfate present, the higher the internal resistance and lower charge capacity of the battery. Thus, it is important to avoid sulfation.

Does it mean If Battery is not full charged frequently, it will loss ability to be full charged later( its capacity decrease) ???

Yes.

John

*Note, a completely discharged battery is somewhat symmetrical, since both electrodes are Pb(II)SO4. It can be recharged in either direction and result in a battery with reversed polarity from the original. That is not good for the battery and is not recommended. Attaching a charger with reversed polarity to a battery can result in an explosion.