12 V SLA Battery Cutoff circuit required

[cyberpks]

Hi All,

Actually I have a 12v 14AH SLA battery and I was wondering :-? that if I can make a auto-cutoff charger for the same, I can easily make a simple charger for the same but I don't know how to get that cutoff section work for protecting the battery to get overcharged. I guess I'll require a voltage comparator (LM324 - I saw it in most of the circuit ideas available) or a relay switch. Any Ideas how do I get that switch working:roll:? I only need the cutoff part and not the charger.Please HELP!!!

 

[Qaisar Azeemi]

I am using IRF3205 N-channel mosfet with the positive rail of the charger with the gate connected to via a GP transistor C828. the transistor is driven by the output of LM741 comparator. so whenever the voltage of the battery reaches to 13.7V the op amp drives the Transistor which grounds the gate and cuts OFF the supply to the battery. this is one of the safest logic that i have successfully implemented to my charger. Try it.

 

[tpetar]

Hi All,

Actually I have a 12v 14AH SLA battery and I was wondering :-? that if I can make a auto-cutoff charger for the same, I can easily make a simple charger for the same but I don't know how to get that cutoff section work for protecting the battery to get overcharged. I guess I'll require a voltage comparator (LM324 - I saw it in most of the circuit ideas available) or a relay switch. Any Ideas how do I get that switch working:roll:? I only need the cutoff part and not the charger.Please HELP!!!

You need complete battery charger, not just cutoff voltage solution.

Do you need simplest as possible or with uC ?

I advise that you first read some article about lead acid batteries and ways of charging of them. Also get manufacturer datasheet about your battery and see data about max allowed charging current or consider C/10, in your way 1,4A.

Post existing circuit of charger if you have.


There is tons of circuits on Internet and on EDABoard forum, just use search option.

 

[cyberpks]

I am using IRF3205 N-channel mosfet with the positive rail of the charger with the gate connected to via a GP transistor C828. the transistor is driven by the output of LM741 comparator. so whenever the voltage of the battery reaches to 13.7V the op amp drives the Transistor which grounds the gate and cuts OFF the supply to the battery. this is one of the safest logic that i have successfully implemented to my charger. Try it.

Can you post a circuit diagram for the same.

 

[tpetar]

Can you post a circuit diagram for the same.

Of course my friend, but you didnt answer on my question :

Do you need simplest as possible or with uC ?

 

[cyberpks]

You need complete battery charger, not just cutoff voltage solution.

Do you need simplest as possible or with uC ?

I advise that you first read some article about lead acid batteries and ways of charging of them. Also get manufacturer datasheet about your battery and see data about max allowed charging current or consider C/10, in your way 1,4A.

Post existing circuit of charger if you have.


There is tons of circuits on Internet and on EDABoard forum, just use search option.

Check this out https://www.circuitstoday.com/simple-battery-charger-circuit.

Here a simple ammeter can be used to detect the complete charge of the battery but it can't be left off without shut down. I mean there should be a person who would keep an eye on the ammeter for its reading to get to 0 and then switch off the circuit. But I want a solution where the charger automatically cuts off the charging. Any Ideas how we can change this circuit to cut-off one.
Can't we introduce some other device that detects this 0 amps (of ammeter) to cut down with a relay switch or some other mechanism.

Of course my friend, but you didnt answer on my question :

Do you need simplest as possible or with uC ?

Ok, let it be the simplest one.

 

[tpetar]

I was afraid exactly of that, and I suspect on bad design. This cannot be used as good charger, with this you can charge bad neighbor battery not yours, just look voltage which you give to battery, also capacitor should not be used, cells will should rest in pulsed current, for some uC controlled chargers on end of charging process, chargers go to float charge with one skiped half-periode with float charge voltage (not trickle chargers):

I strongly dont recommend this design !!! Maybe in mad Max movies.

At first, any person who whant to design and build battery chargers must know battery needs, charging/discharging ways, and accept manufacturers proposal. Also battery life depends from way of usage, environment, aging, duty cycle, temp, charging/discharging ways.... and many other parameters.

For start see this link :

Charging Lead Acid



You cant charge that 12V 14Ah battery with 5A current, You should respect C/10 lead acid charging. That meas 14Ah/10=1,4A max current. That means that You can use LM317 IC for simple float charger, because LM317 IC have auto current limit to 1,5A.


You can see some examples of simple circuits :

https://www.eleccircuit.com/6v-or-12v-lead-acid-battery-charger-using-lm317/

https://www.circuitstoday.com/battery-charger-circuit-using-lm317


Float charge voltage depends from temperature and should be 13,5V-13,8V at 25C (12V 6 cells).
Lead Acid is full when battery voltage OCV shows 12,72V-12,73V. 2,12V per cell (measured 24h after charging).
Maximum discharging for starter batteries without load should be 11,9V or 1,98V per cell.

We speak about starter lead acid batteries, for deep cycle there is other datas.

All things can be done somehow, on good or bad way. If you whant long life for your battery with good capacity you should have good charger and carefully disharge. Also environment terms like temperature, vibrations, moving,... have very important rule for battery health.

 

[cyberpks]

I was afraid exactly of that, and I suspect on bad design. This cannot be used as good charger, with this you can charge bad neighbor battery not yours, just look voltage which you give to battery, also capacitor should not be used, cells will should rest in pulsed current, for some uC controlled chargers on end of charging process, chargers go to float charge with one skiped half-periode with float charge voltage (not trickle chargers):

...................

Thanks for your help ;-), the third circuit that you have mentioned is a good choice. This circuit as mentioned in the site will automatically reduce the current and will shift to trickle charge when the battery is fully charged.

One more circuit that I have found,

This may be an alternate, and it is quite simple as well. May be I should try this one.

 

[tpetar]

This may be an alternate, and it is quite simple as well. May be I should try this one.

Yes my friend, try why not. :wink:

 

[cyberpks]

Yes my friend, try why not. :wink:

Really appreciate your help, Thanks.
Well, what you have mentioned is "LM317 IC have auto current limit to 1.5A" and it is also mentioned that the charge current should be 1/10 of the battery's AH rating so I must assume that it'll take approx 10-11 hours of time to charge it completely. Can't we decrease that time span for some fast n hot charging.... :?

 

[tpetar]

Really appreciate your help, Thanks.
Well, what you have mentioned is "LM317 IC have auto current limit to 1.5A" and it is also mentioned that the charge current should be 1/10 of the battery's AH rating so I must assume that it'll take approx 10-11 hours of time to charge it completely. Can't we decrease that time span for some fast n hot charging....:?

Of course everything is possible, I saw some people charging mobile phone battery on 12V lead acid direct!

You can use LM350 its 3A, this will make charging process faster or LM338 its 5A, but you must know battery health will suffer.

There is way with uC guided fast chargers which can charge 55Ah per 1h of time (C/1), but my suggestion just as almost all lead acid battery manufacturers is to avoid this. Also lots of people appearing with fishing stories about this. What you think when people eat food, does people love to take whole big pizza in 1min or to eat for longer time? (I consider that that people have normal apetite, and usual/normal frequncy of eating).

I have several car lead acid batteries 13 years of life and still working and have good internal resistance and capacity. Last winter they cold crank car on -20C on LPG without problem, just for testing. Of course I use them for other purposes not in car.

 

[cyberpks]

Ok, do you have any idea about how will **broken link removed** work?

 

[tpetar]

Ok, do you have any idea about how will **broken link removed** work?

My friend, there is proverb "Ammount of music according to ammount of money."




I think maybe is smart thing for start to buy one small fire extinguisher, to have in just case near hands, when you experimenting with this circuits.

Before few month one "expert" try to charge car battery only with trafo AC current. :smile:


Always when working with lead acid batteries I suggest to always have near baking-soda, few liter of water, and wear protecting googles for eyes. Specially if you dont know what you are doing. Lead acid batteries can explode in some conditions and can make sirious damage to property and body. Dont play with this.

 

[Qaisar Azeemi]

My friend, there is proverb "Ammount of music according to ammount of money."




I think maybe is smart thing for start to buy one small fire extinguisher, to have in just case near hands, when you experimenting with this circuits.

Before few month one "expert" try to charge car battery only with trafo AC current. :smile:


Always when working with lead acid batteries I suggest to always have near baking-soda, few liter of water, and wear protecting googles for eyes. Specially if you don't know what you are doing. Lead acid batteries can explode in some conditions and can make serious damage to property and body. Don't play with this.

so what happens to the battery when "expert" tried to charge it with pure AC ? was it Exploded? Boiled? an intrusting experiment. here in our office such and "Expert" shorted the Terminals of a 200AH Lead Acid battery and it Exploded out? ha ha ha..... ;-)

as i think Lead acid batteries are the safest batteries. they can not explode even if they get overcharged they just boiled and then dried out.

for the charger circuits you have shown above have no cutoff circuitry. and the original post is about cutoff circuit. zener diodes and Transistor combinations do not cut the supply OFF as effectively as you may expect from it. I there for used an N channel mosfet before the input of the Lm317 or LM338; with the gate of the mosfet is driven by a Comparator IC. try this circuit and get Fantastic cutoff result .

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[tpetar]

so what happens to the battery when "expert" tried to charge it with pure AC ? was it Exploded? Boiled? an intrusting experiment. here in our office such and "Expert" shorted the Terminals of a 200AH Lead Acid battery and it Exploded out? ha ha ha..... ;-)

as i think Lead acid batteries are the safest batteries. they can not explode even if they get overcharged they just boiled and then dried out.

for the charger circuits you have shown above have no cutoff circuitry. and the original post is about cutoff circuit. zener diodes and Transistor combinations do not cut the supply OFF as effectively as you may expect from it. I there for used an N channel mosfet before the input of the Lm317 or LM338; with the gate of the mosfet is driven by a Comparator IC. try this circuit and get Fantastic cutoff result .

- - - Updated - - -

Lead acid dont need cutoff they can stay on float charge voltage, they dont need cutoff. Of course charger can be made like that when charging cycle finished then turn off charger. Point of this chargers is to slow down current. Charging of Lead Acid batteries should be controlled over current.

Lead Acid can explode its very dangerous battery in several aspects, one chemical with dangerous chemical gases and liquid and second on 14,2V-14,4V and over that, water from cells start evaporating and production of hydrogen gas started. Hydrogen and small spark can give explosion.


Exploded batteries:
http://www.onlinecomponents.com/blog/52-adopt-safe-battery-handling-practices.aspx




also read this

http://jgdarden.com/batteryfaq/carfaq14.htm

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This link will be useful to read:

http://www.vonwentzel.net/Battery/00.Glossary/

 

[Qaisar Azeemi]

Lead Acid can explode its very dangerous battery in several aspects, one chemical with dangerous chemical gases and liquid and second on 14,2V-14,4V and over that, water from cells start evaporating and production of hydrogen gas started. Hydrogen and small spark can give explosion.

- - - Updated - - -

But my 3 stage charger charge the battery up to its boost voltages i.e; 14.5V...... y is it not exploded???

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[tpetar]

But my 3 stage charger charge the battery up to its boost voltages i.e; 14.5V...... y is it not exploded???

We drink water, and we dont die. Water can kill. :smile:

For some situation several terms must be fulfilled.

Try to give 14,5V to full battery, and wait that water is losed and lead plate is in air, wait some time that some hydrogen is produced and give some spark on terminals. :smile: Or put discharger battery with air exposed lead plates to your charger. :smile:

Of course I dont recommended this.

When a lead-acid battery is recharged, some of the electrolyte may evaporate and hydrogen gas will escape from the battery cell vents. Hydrogen gas is flammable, so lead-acid batteries should be stored and recharged away from any sources of fire or flame.

During normal operation, water is lost from a non-sealed (or flooded) battery due to evaporation. During charging, lead acid batteries produce hydrogen and oxygen gases (highly flammable/explosive) as electrolysis occurs.

Many lead acid explosions are believed to occur when electrolytes are below the plates in the battery and thus, allowing space for hydrogen/oxygen to accumulate. When the battery is engaged, it may create a spark that ignites the accumulated gases and causes the battery to explode.

If your charger give 14,5V on finish of charging process replace charger, its bad charger.

You can see example of explosion on youtube video is "Car Battery Explosion - Acid Shed".

People unfortunately best learn from some accident. :sad:

 

[Qaisar Azeemi]

my charger is heating up the battery. battery is new. initially its charging was normal and it was getting charged without heating up with the same 3 stage charger which is charging it with 10A and also it cuts of when battery got fully charged. but now during charging the battery got heating up? what can be the reason and what is the remedy.

 

[tpetar]

Its simple, your battery charger make wonder, he transform new into bad battery.

Battery should not go worm during charging process. This is common for fast chargers, and its normal for this situation but its bad for battery.

Check stages during charging. Check internal resistance of your battery, its increased probably.

Best timing to charge lead acid is within 10 hours or more, but starting immediately after discharging, and avoiding big discharging, discharge it max 30%, this will give longer life for battery (for starter).

 

[Qaisar Azeemi]

How? i am wondering about that. it is written on the charger that it is a 3 Stage Automatic charger. my battery is 115AH and it charges the battery with a constant current of 10A (C/10 approx and when the battery gets most of its charge it gradually reduces the current and when battery is fully charged it cuts OFF. its behavior is normal. another point is that i placed the battery on a place where there is no or less Ventilation but now i placed the battery at open place to provide panty of air to keep it cool. plates of the battery are now darker then the new battery................... :-( ..... and the battery is approximately 3 months old...... :-(