About how to control overcharging and over discharging of lead acid battery using microcontroller.

Reloadron

Joined Jan 15, 2015
5,646
Hi sir
I have some ambiguity about how to control overcharging and over discharging of lead acid battery using microcontroller. If it is your pleasure help me please.
This thread dates back to 2012. You would do well to start a new thread asking your question(s). Describe your ambiguities in detail. You may also want to read what is covered at Battery University regarding the charging of lead acid type batteries.

Ron
 

MrAl

Joined Jun 17, 2014
7,813
Hi,

Over discharging is easy. Just detect the lowest voltage you should be using with your battery and shut off until it is charged again later.

Over charging is another story though. This could mean you want to control the charge cycles or you just want to protect against an accidental over charge.
 

MisterBill2

Joined Jan 23, 2018
7,035
Although this is an old thread, the way to avoid an overcharge is to limit the charging source voltage to the acceptable "float charge" voltage level. That voltage is available from the battery maker, it is the voltage that can be applied continually without causing any damage.
 

MrAl

Joined Jun 17, 2014
7,813
Although this is an old thread, the way to avoid an overcharge is to limit the charging source voltage to the acceptable "float charge" voltage level. That voltage is available from the battery maker, it is the voltage that can be applied continually without causing any damage.
Hi,

Yeah good idea. That's the way i used to do my lead acid batteries. Connect them to the power supply through long jumper leads with resistance so as the voltage went up the current went down, until the voltage of the battery was very nearly the voltage of the power supply then the current was extremely low effectively zero.
 

crutschow

Joined Mar 14, 2008
25,441
how to control overcharging and over discharging of lead acid battery using microcontroller.
Below is the recommended 3-stage charging sequence for a lead-acid battery from Battery University, that Reloadron referenced.

You would need to measure and control both the voltage and current from the charger with the microcontroller, and adjust them accordingly.

The 1sl-stage constant-current charge value is determined by the recommended value for the specific battery size (typically about 1/10th its AH capacity).

The 2nd-stage constant-voltage topping charge is the highest allowed charging voltage (typically about 2.4V/cell).

The 3rd-stage drops the voltage to a lower float charge value (typically about 2.25V/cell) when the charge current drops and levels off at a nominal low value
That prevents the battery from being overcharged.
1575099329159.png

Over discharging is simply done by disconnecting the load when the battery voltage drops below a specific voltage.
For standard lead-acid batteries you generally don't want to discharge the below about 50% of capacity or 2.05V/cell, for best life.
 

Tonyr1084

Joined Sep 24, 2015
5,081
Many years ago I worked for an emergency lighting company that serviced emergency lights. Most were the 12 volt kind you saw in K-Marts all over the US. Hotels typically have smaller units in the hallways and the exit signs were also lit via battery during power failures. Bigger systems used generators at hospitals and movie theaters. But we're not here to discuss generators.

On a typical 12 volt SLA battery we'd set the float charge at 13.6 volts. Batteries were maintained at a constant voltage and if memory serves - they were charged through a small incandescent lamp. So when the battery was drawing a high amount of current (sorry can't define what that current was - probably around 5 amps max) the lamp would glow brightly. But as the battery voltage came up to float level the lamp would dim out. In some cases the lamp would always glow even a little but in most cases the lamp would go so dim you couldn't tell if there was any current going into the battery at all.

Today I have a charger in my garage. I converted a 12 volt wall wart (5 amp) into a 13.6 volt (less amp) float charger and keep it on a battery that has been on the shelf for around 2 1/2 years now. That battery is typically used to play a car radio when I'm out there using the garage as a wood shop. Honestly couldn't tell you if the battery has its full capacity, but every so often I check the voltage just to see how things are going. Test #1 is to check for 13.6 volts. Test #2 is to disconnect the charger for an hour and to check for battery voltage of at least 12.4 volts. Test #3 is to turn the radio on and watch the voltage. If it's dropping fast then I'd surmise the battery has reached the end of its life. So far all three tests show the battery to be in decent condition. I suspect that if the need arose it could be thrown into a car and used to start it up. Wouldn't take any long trips on it though. It IS an old battery. In fact, it came out of my friends van - after he burned it up (no coolant). He had the battery for a few years before donating it to me.

For my experience, keeping a battery maintained at 13.6 volts has caused no harm.

[edited] researched my threads regarding my battery charger modification. It was posted May 2017 so it was 2 1/2 years ago and not the 4 years ago I thought. Here's a link: AND PLEASE DO NOT POST ANY COMMENTS THERE - THE THREAD IS OLD AND DOES NOT NEED TO BE REVIVED. If you have questions you can PM me. —> the link: https://forum.allaboutcircuits.com/threads/modifying-smps-from-12-volts-to-13-6-volts.135256/
 
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