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Lead acid battery full charge voltage

mrinalmani

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Hello everyone
What I understand is that a fully charged flooded lead acid battery measures 12.6V.
But different sources mention different charging voltages, such as 13.6V or even as high as 14.6V.
Especially for automobile batteries, multiple sources say that the alternator voltage should be around 14.5V.
This is confusing. When the battery charges fully at 12.6V, why do we need higher voltage?
What is the critical maximum voltage? If we had to set a charging voltage, would it be 12.6V or 13.6V or perhaps even higher?
Thanks
 

KlausST

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Hi,

I think it's well documentend.
Just lookfor dokuments at:
* battery manufacturers
* charger manufacurers
* charger IC manufacturers
* universities

There are internet sites like batteryuniversity.com.

13.6V vs 14.4V:
See it like a glass that you want to fill (charge) from a bottle.
--> Let's say the glass is full when filled up to 13.6cm. But during filling up you may lift the output of the bottle higher than this 13.6cm, maybe 14.4cm.
just to ensure (enough) water can flow out of the bottle into the glass.

Or when filling a tyre with air..
It's different wheter you want to fill in air... or just keep the pressure

Klaus
 

crutschow

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You need a voltage significantly higher than the normal charged voltage to have significant charging current.
Even a partially discharged battery will charge very little with 12.6V charging voltage applied.
Typically using a smart external charger, a 12V lead-acid battery is charged until it reaches about 14.5V, held at that voltage until the charging current drops, and then the voltage is set to about 13.6V for maintenance (trickle) charge.
These voltages vary some with the battery temperature.
 

mtwieg

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You should be familiar with three level charging. Battery university has a good description here: https://batteryuniversity.com/article/bu-403-charging-lead-acid 

Basically there are two important voltages you need to determine for your lead acid battery. The float voltage (aka standby voltage) is the highest voltage you can apply indefinitely without significantly degrading the battery's lifespan. Usually this is around 2.3V per cell. Why would you ever want to exceed the float voltage then? Because charging at the float voltage takes a very very long time. That's where the absorption charging phase comes in. Here a higher voltage, the absorption voltage, is applied, but only for limited periods of time until the battery is near 100% SOC. The absorption voltage is generally 2.4-2.45V per cell.

Any decent manufacturer of PbA batteries should recommend specific voltages to you.
 

Easy peasy

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lead acid batteries are float charged at 13.5V for 12V, 27V for 24V, 54V for 48V ....

wet cell batteries can be equalise charged ( to stir up electrolyte ) at up to 16V for short periods
 

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