Why do they call them 12/24 volt batteries?

[Timbeck2]

12 volts on a 12 volt battery is too low. I ran across this chart, some may know it, some may not.

Recommended Bus Voltage
Temp. 12V Battery 24V Battery
120F 13.8 volts 27.5 volts
90F 14.0 volts 28.0 volts
60F 14.3 volts 28.5 volts
30F 14.5 volts 29.0 volts
<0F 14.8 volts 29.5 volts

Just thought I'd share.

 

[GRG55]

There needs to be a differential between the bus or source voltage and the battery or it won't charge. Something about the electrons having to be "forced" into that little plastic battery container against their will.

I always thought if the battery was lower than the alternator then the electrons would just flow downhill into it. Apparently not...

btw, those little covers that parents of young children like to put on the electrical outlets in their homes...they aren't really for child protection. They are to keep the electrons from flowing out and making a big mess on the living room floor.

 

[Bell206]

12 volts on a 12 volt battery is too low.

FYI: There are 2 separate voltage ratings on batteries under different names but basically a running voltage and a neutral voltage. On a "12 volt" battery with 6 cells being actively charged (running) it works out to be 13.2 volts or 14 volts and for a "24 volt" battery it's 28.2 volts. The neutral rating is close to 12.6v and 24.4v.

 

[chemgeek]

12 volts on a 12 volt battery is too low. I ran across this chart, some may know it, some may not.

Recommended Bus Voltage
Temp. 12V Battery 24V Battery
120F 13.8 volts 27.5 volts
90F 14.0 volts 28.0 volts
60F 14.3 volts 28.5 volts
30F 14.5 volts 29.0 volts
<0F 14.8 volts 29.5 volts

Just thought I'd share.

These are charging voltages. There is a quantity known as an "overvoltage" required to overcome the theoretical battery voltage in order to reverse flow of electrons to charge the battery. The amount of overvoltage necessary depends on charging rate and other factors. The output voltage of the battery is determined by the chemistry of the anode and electrode reactions. For lead-acid batteries the theoretical cell voltage is in the neighborhood of 2.1 V per cell, with 6 cells making up a 12 V battery. A fully charged 12V lead-acid battery should actually be around 12.6-12.8 V.

 

[Capt. Geoffrey Thorpe]

Round off to nearest integer before multiplying by the number of cells.

 

[flyingron]

Chemgeek is right. A lead-acid battery is about 2 volts per cell (2.1 if fully charged and not under any load). The BUS voltage is provided by the ALTERNATOR and is higher. It is more correct to say that a 12V battery is used in a 14V electrical system.