is it safe to charge a 12v lead acid battery with 16v?

 

Monitor the voltage across the battery while charging.
Stop charging when the voltage reaches 14.5V.

 

so the lead acid battery have a maximum charging capacity until 14.5 before it gets destroy?

tnx

 

No. The battery voltage will gradually increase as it gets up to being fully charged.
After that electrolysis takes place producing hydrogen and oxygen gases.
The battery gets very hot and creates a potentially explosive situation.
If the battery is a sealed lead acid battery the battery case will start to bulge and melt, like this:

You don't want your battery to reach this stage.

 

Yeah. It magically goes poof at 14.51 volts.

NO. It depends on temperature, the age and health of the battery, and a few other things. I does not magically go poof at 14.51 volts. The simple fact that it is a lead acid battery does not tell all there is to know about that particular battery. Go look at batteryuniversity.com and learn the many factors that affect a lead acid battery, including the Sealed Lead Acid and the Absorbent Glass Mat versions.

 

i noticed the battery is charging every 5 secs in 16v, example 12.0 ~ 12.5 when i remove it from the circuit it, the battery voltage turns to 12v again. how that happen?

 

If you applied 16V from an unlimited source of current with no limiting resistance in series the battery could take a very high charge current of perhaps several hundred amps and go poof (or perhaps blooey) in short order. You need some method (either a resistor or a current limiter) to limit the maximum charging current to whatever the particular battery can safely tolerate.

 

It's not exactly safe to charge at 16v since that would be like forcing an enormous amount of power all at once. However, that depends on how many amps your charger is. If it can charge it without dropping much in voltage then it would be charging too fast, which would eventually cause the battery to get extremely hot resulting in a dangerous environment.

As stated before put a separate load (resistor/light bulb/etc) in series with the battery and charger to draw some of the current away so it will not stress the battery as much. Most 12v lead acid batteries fully charge around 14.4v anyway.

 

It's not exactly safe to charge at 16v since that would be like forcing an enormous amount of power all at once. However, that depends on how many amps your charger is. If it can charge it without dropping much in voltage then it would be charging too fast, which would eventually cause the battery to get extremely hot resulting in a dangerous environment.

As stated before put a separate load (resistor/light bulb/etc) in series with the battery and charger to draw some of the current away so it will not stress the battery as much. Most 12v lead acid batteries fully charge around 14.4v anyway.

I don't mean to be contradictory, but I don't think this is true. I regularly use a capacitive transformer that limits CURRENT (1 amp or so.) A heavily sulfated battery can often be revived by applying 120VDC (not a typo) to it. No damage happens at all. (Although dealing with those voltages, utmost care must be taken as handling mistakes could be lethal.) As is the case with most electrochemical reactions, the cells will only rise to the voltage needed to pass current. As the voltage across the cells drops, the current rises (which is why current needs to be limited, or it would certainly damage it.) The higher voltage can overcome the sulfation resistance and start moving current, breaking up the sulfation.

I've seen voltage rise close to 50 volts on starting, with very little current moving, and then gradually lower to normal levels as current raises to the 1A limit of the capacitor. Overcharging can still happen, which is wasteful and burns off water (and can be dangerous because H2 is explosive.)

Nevertheless, it is worth mentioning that it's more complicated than forcing power into the cells. It just doesn't work that way.

 

...I don't think this is true...

Maybe not always, for example in the case you note where the battery has extremely high internal resistance. But it is certainly true for the normal case of a well-maintained battery. And even in the case you noted, the charger quickly drops into current-regulation mode once the hurdle is overcome.

Charging a 12V battery with unlimited current at 16V would be a very bad idea.

 

Maybe not always, for example in the case you note where the battery has extremely high internal resistance. But it is certainly true for the normal case of a well-maintained battery. And even in the case you noted, the charger quickly drops into current-regulation mode once the hurdle is overcome.

Charging a 12V battery with unlimited current at 16V would be a very bad idea.

Completely agree! My point was not well stated. The point: CURRENT is actually more important than voltage above the point that allows current to flow. Moderating the voltage supplied in a normal battery is one way of limiting current. The lower voltage (say 13.2V) reduces current flow significantly. (Floats)