# 12VDC Battery Question

#### mpcotuong

Joined Aug 26, 2010
170
Hi All,

I am using 12VDC battery for my circuit. How do I know when I need to recharge the battery? Do you have any circuit to tell that the battery need to recharge by display LED?

Thanks,
Kevin

#### crutschow

Joined Mar 14, 2008
33,342
What type of battery?

#### mpcotuong

Joined Aug 26, 2010
170

Thanks,
Kevin

#### crutschow

Joined Mar 14, 2008
33,342
Then you just use a comparator set to trip at about 12V (12.6V is full charge). That will indicate a discharge of the battery to about the 50% point. Going lower than that will tend to shorten the life of the battery.

#### mpcotuong

Joined Aug 26, 2010
170
What is the voltage need to recharge? can you more specific? Anh if you have the circuit is great.

Thanks,
Kevin

#### Vahe

Joined Mar 3, 2011
75
If this is an automotive lead acid battery, then you may be able to use the technique that is used there. The alternator voltage is regulated at about 14.2V or so that the terminal voltage at the battery is about 13.5V. This is to account for the voltage drops along cables. So I think if you can have the terminal voltage at about 13.5V, you can push current into the battery to charge it. The open-circuit voltage of the automotive lead-acid battery is about 12.6-12.8V (2.1-2.15V per lead acid cell, 6 cells per battery pack).

#### mpcotuong

Joined Aug 26, 2010
170
Thanks, Vahe for explain but I need circuit to tell once need recharge the battery?

Kevin

#### stanman11

Joined Nov 23, 2010
228

#### mpcotuong

Joined Aug 26, 2010
170
Thanks, Stanman11. It help. I will try it.

Kevin

#### stanman11

Joined Nov 23, 2010
228
Thanks, Stanman11. It help. I will try it.

Kevin

#### Bernard

Joined Aug 7, 2008
5,784
Kevin, I think you have a low battery warning ckt mixed in with weight dpop ckt. composed of a LM 393 comp, V divider, precision ref Lm 385Z- 1.233 V, & red LED.

#### mpcotuong

Joined Aug 26, 2010
170
Thanks, Bernard. You mean the reference circuit you sent to me last time?

Kevin

#### Bernard

Joined Aug 7, 2008
5,784
Before that- think it may be in picture file

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#### mpcotuong

Joined Aug 26, 2010
170
Thanks, Bernard so much.

Kevin.