Why exactly 13.8V is special?

[Willen]

I found few circuit which recomends 13.8V DC as a final supply. Why they are saying exactly 13.8V? Related to cell of battery?

 

[KeepItSimpleStupid]

Think of it as (13.8-12)/12 or about 150 mV per cell of a 12 V battery. It can safely be supplied continuously without overcharging the battery.

An Automobile's electrical system is about 13.8 V with the engine running and not 12. 13.8 V is the operating voltage. The battery can actually dip to about 8 v when starting. When starting a vehicle, most loads are disconnected during start. i.e. Note the radio goes off.

 

[MikeMl]

13.8V is the nominal voltage used to "maintain" a sealed lead acid (AGM or RG or VRLA) 6-cell battery. Such a battery, when fully charged, will measure ~12.85V at room temperature, 24 hours after being disconnected from the charger, provided it is isolated from any load. During recharging, the voltage can rise to as much as 14.7V.

13.8V is too low to recharge a flooded-cell lead acid battery, and is too high to float the battery for long periods of time. Most commercial chargers float at ~13.2V. Automobile charging systems typically hold the battery at 14.2V to 14.5V while the engine is running.

 

[Nigel Goodwin]

I found few circuit which recomends 13.8V DC as a final supply. Why they are saying exactly 13.8V? Related to cell of battery?

To make it even simpler than the previous answers - 13.8V is simply the nominal voltage of a standard 12V car battery.

 

[Willen]

I found it on few basic RF amplifier circuits on internet.

 

[Nigel Goodwin]

I found it on few basic RF amplifier circuits on internet.

That because they are intended for in-car use

 

[cowboybob]

Off topic message.

KISS, your PM in-box is full and won't accept any new messages.

I apologize for the intrusion into this thread.

CBB

 

[MrAl]

Hi,


Yeah usually when they state 13.8v they mean it is meant to work from a car battery, running engine or not even though it is a little lower when not running.

The actual voltage of a battery partly depends on temperature too, but i think they usually state voltages for around 20 deg C without stating any specific temperature.