# Potential Difference between Charger and Battery

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#### abdulwahababid

##### Member level 3
What will be ratio of voltages between charger and battery in order to charge the battery safely and without reducing the life of battery.

e.g
if the battery is of 12v/10Ah(car battery) then how can I select the voltages of the charger.

I am asking as general. car battery is an example to explain my question.

Charger Voltage should be how much greater than that of battery...!!!!!

any (x)battery, any (?)charger...

charger voltage>how much of battery voltage.

I'm not asking about particularly of car battery. I am talking about general concept of battery and charger

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#### fethiyeli

##### Full Member level 4
The battery voltage should not exceed 13.8V for long periods and 14.4V for short periods. (8hours maximum)

ı have taken this information from battery charger guide document.

#### abdulwahababid

##### Member level 3
ı have taken this information from battery charger guide document.

I was asking as general. car battery was an example to explain my question.

Charger Voltage should be how much greater than that of battery. any formula or concept to explain this

#### tpetar

What will be ratio of voltages between charger and battery in order to charge the battery safely and without reducing the life of battery.

e.g
if the battery is of 12v/10Ah(car battery) then how can I select the voltages of the charger.

I am asking as general. car battery is an example to explain my question.

Use battery manufacturers datasheet. Lead Acid 12V have 6 cells, each cell is charged is full at 2,12V.

Float charging 13,8V 2,3V x6
Cyclic charging 14,4V 2,4V x6

* According to temperature this voltages can be changed.

Max charging current for that 10Ah battery should be around 1A, but check datasheet.

That small batteries usually are constructed for C/20. General Lead acid (starter) is C/10.

For car battery (starter lead acid) use C/10 that means discharging and charging in 10h. That time will keep battery healthy and battery in that time can give declared capacity.

Lead Acid charging stages graph :

I personally skip usage of Equalisation step.

Battery can stay long on float charge voltage, as in standby mode, but cycling voltage should be used only for charging cycle of discharged battery.

Its very important to limit current when you charge discharged battery.

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#### abdulwahababid

##### Member level 3
Use battery manufacturers datasheet. Lead Acid 12V have 6 cells, each cell is charged is full at 2,12V.

Float charging 13,8V 2,3V x6
Cyclic charging 14,4V 2,4V x6

* According to temperature this voltages can be changed.

Max charging current for that 10Ah battery should be around 1A, but check datasheet.

That small batteries usually are constructed for C/20. General Lead acid (starter) is C/10.

For car battery (starter lead acid) use C/10 that means discharging and charging in 10h. That time will keep battery healthy and battery in that time can give declared capacity.

Lead Acid charging stages graph :

View attachment 87895

I personally skip usage of Equalisation step.

Battery can stay long on float charge voltage, as in standby mode, but cycling voltage should be used only for charging cycle of discharged battery.

Its very important to limit current when you charge discharged battery.
Charger Voltage should be how much greater than that of battery...!!!!!

any (x)battery, any (?)charger...

charger voltage>how much of battery voltage.

I'm not asking about particularly of car battery. I am talking about general concept of battery and charger

#### tpetar

Charger Voltage should be how much greater than that of battery...!!!!!

any (x)battery, any (?)charger...

charger voltage>how much of battery voltage.

I'm not asking about particularly of car battery. I am talking about general concept of battery and charger

For start you should not change original question in first post, because this change meanings of all other posts.

Each battery chemistry have their voltage and charging method, charging methods are different, voltage also.

I give you answer for lead acid that is what zou ask in first post before modification.

12V Car Battery (starter type of lead acid) voltage is in range from 11,9V to 12,73V
Charger in float charge voltage is 13,5V-13,8V
Cyclic charging voltage si 14,4V

#### abdulwahababid

##### Member level 3
For start you should not change original question in first post, because this change meanings of all other posts.

I'd not change my question but only explained further

#### tpetar

Battery voltage is measured 24h of resting time, after charging process stops.

If you use float charger just use this 13,8V - 12,73V = 1,07V difference. This is when battery is full of charge, and its stay on float charger.

If battery is empty 40-50%, lets say 13,8V - 12,50V = 1,3V difference.

I'd not change my question but only explained further

If you are interesten in Li-Ion max charging voltage is 4,20V per cell and cell should go up to this level, after charging process is terminated. Charger should be current limited and controlled, also with temperature monitoring and protection. Minimal voltage is 2,75V.

NiMh have top charging voltage up to 1,45V - 1,5V, full battery is at 1,25V empty at 1V.

#### ZASto

@abdulwahababid:

Yesterday, 20:25
Last edited by abdulwahababid; Today at 15:08.

And tpetar gave you some examples based on a LedAcid batteries.

There is no "universal equation" that will answer your question, as it varies with battery chemistry (LedAcid, NiCd, NiMH, LiIo, LiPo, ...)

Do not be so stubborn, it can hurt your head as you try to break a wall with it. :grin:

#### abdulwahababid

##### Member level 3
@abdulwahababid:

And tpetar gave you some examples based on a LedAcid batteries.

There is no "universal equation" that will answer your question, as it varies with battery chemistry (LedAcid, NiCd, NiMH, LiIo, LiPo, ...)

Do not be so stubborn, it can hurt your head as you try to break a wall with it. :grin:

Yes I explained my question added further lines not change the question.

There is no "universal equation" that will answer your question, as it varies with battery chemistry (LedAcid, NiCd, NiMH, LiIo, LiPo, ...)

i just want to know equation nothing else if it exist.As u said it is not. its fine than no explanation was asked by me

#### bill66656

##### Member level 2
Dear abdulwahababid,

First, you'd better get to know the process of charging: trickle charge, CC and CV.

Consider it in this way:

If CC(constant current) stage needs 1A charging, and the resistance between the source and the battery is 1 Ohm, Also if the battery will be charged to 10V (CC stage will end at this threshold when it's reached) in your car battery case, then the source should be at least 10+1=11V. but if the resistance is 4 Ohm, the souce should be at least 10+4=14V.

So in the 1 Ohm situation, the source needs to be at least higher than 12V, but in the 4 Ohm situation, the source needs better to be at least 14V. While, if it doesn't reach 14V, only longer charging time I think, won't do severe harm.

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abdulwahababid

### abdulwahababid

Points: 2

#### tpetar

Car starter lead acid battery, 55Ah range of size, as new or battery is in good health, internal resistance should be less then 10mΩ, if internal resistance is higher then 25-30mΩ, battery should be replaced. Batteries with higher then 90mΩ can have sirious battery case deformation, and for sure heating, during charging process.

abdulwahababid

### abdulwahababid

Points: 2

#### abdulwahababid

##### Member level 3
thank you bill6656 & tpetar...
now i m not confuse...

#### tpetar

Sneak around and search some charger circuit, maybe you will get some additional idea.

Try to understand how charging circuit works, read description of projects.

Read battery tutorials for charging, discharging, general informations,.....

Internet is free for all.

;-)

#### babatundeawe

##### Full Member level 5
please can you explain a little on current limiting in battery charging. it gets me a little confuse.

does it mean dat you measure the charge current (take for instance a shunt resistance place on the the low side for cuurent measurement). do i use this ti stop the charging process or what?

again how can i ensure a constant current for charging?

thanks

#### bill66656

##### Member level 2
Dear Tpetar

'Car starter lead acid battery, 55Ah range of size, as new or battery is in good health, internal resistance should be less then 10mΩ, if internal resistance is higher then 25-30mΩ, battery should be replaced. Batteries with higher then 90mΩ can have sirious battery case deformation, and for sure heating, during charging process.'

I don't doubt your knowledge about lead-acid battery. The resistance I mentioned is that from source to the contact on battery, and it includes the pass transistor's and the leads (charger's pass transistor). The 'large signal' resistance of the pass transistor will depends on its bias, but it will be smaller at the end of CC stage, so this resistance should be adopted in my method.

Thank you for your comment anyway.

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