12V LM350T Lead Acid battery charger question

[khatus]

Hello friends, I want to make this lead acid battery charger.

Here, I want to use 1000pF polyester film capacitor instead of the electrolytic capacitor C3? My first question is can I use 1000pF polyester film capacitor instead of 1000pF electrolytic capacitor?

if i use the DPDT Self-Locking Push-Button Switch, in the place of the S1 Start pushbutton, will there be any problem?

 

[betwixt]

I have no idea why electrolytic is shown in the diagram, the part is not critical and any non-polarized capacitor should work.
Pin 1 is really for internal compensation and not intended to be grounded at all but I don't think any damage will occur if a latching switch is used. I think I would try adding a resistor (100 Ohms?) in series with the switch, if it still works it would be safer. Only in series with the switch, leave the capacitor between pins 1 and 8 or it might oscillate.

Brian.

 

[khatus]

Will there be a problem if I use 15 ohm and 230 ohm 1/4 watt resistors? The value of these two resistors must be high wattage or low wattage? If it is high wattage then how much wattage should I use?

 

[danadakk]

I did a sim of grounding that pin, and sim showed no reak effect on output.
So my guess is Spice model not complete. Looks like Q9/10/12/13 off, so
output goes high allowing LM350 to function as 2A current source ? So
button must be momentary ?

Current thru R2/R3 limited by 15K R4, so low wattage should be fine.

 

[khatus]

Hello friends,I have completed soldering of the circuit on perfboard according to this Lead acid battery charger diagram, and got the exact output according to the formula given in the datasheet.Here is my resistor value,

R2+R3 = 239.6 k Ω
R1 = 3.276 k Ω
According to the formula given in the LM350T datasheet,

Vout = 1.25×(1+ 3276/239.6) + 50×10-6×3276
Vout = 18.34+0.1638
vout = 18.50
and I have got exactly this output voltage.
Now my question is,
1) charging a 12-volt lead-acid battery with this 18.5v output voltage cause any damage to the battery?
2) What is the optimum output voltage to charge the 12V lead acid battery if it is not charged at 18.5 volt.
3) What is the purpose of the 15KΩ resistor in the circuit?
4) If I make the output voltage slightly higher than 12 volts (say 13.5 volts) will the LM301A OPAMP would work properly? Because it requires +/-15 volts at pin 7,4.

--- Updated Nov 3, 2024 ---

Here is my circuit,

 

[KlausST]

Because it requires +/-15 volts at pin 7,4.

It REQUIRES? Where is this information from?

From Datasheet:

DESCRIPTION
The LM101A is a general purpose operational am-
plifier which offers many features: supply voltages
from ±5V to ±22V,

Klaus

 

[betwixt]

.. and yes, 18.5V will fry your battery although the regulator might fry first!
Check with the battery manufacturer but typical charging voltages for 12V lead acid batteries is between 13.2V and 13.8V.

Brian.

 

[danadakk]

Battery ref Handbook, attached.

 

[KlausST]

Hi,

Check with the battery manufacturer but typical charging voltages for 12V lead acid batteries is between 13.2V and 13.8V.

This 13.2V ... 13.8V is the so called float charge voltage .. just to keep the batteries charged.
But indeed it´s not very healthy if the batteries are not "discharged" from time to time due to their memory effect.

*****

There are many good and reliable informations about how to charge a lead acid battery. Nothing is hidden, everything is free to download.
So most battery manufacturers provide informations on how to charge (and discharge) them. ..depending on their use case.
* for fast charging
* for high lifetime
* for high cycle count
* for high capacity usage
* for high efficiency
* for long "lazy time" like in an USV, where it may be unused for years (kept charged)
* for high current draw like for a car starter
* for different temperatures ...
and so on.

And for sure not every lead acid battery is the same. There are different ones, optimized for the one or the other use case.

So it´s on the designer to decide on what to focus. And according this .. what charging type and parameters to chose.
And to keep the life time high .. you even my discharge the batteries from time to time , maybe even with ratherh igh current pulses.

There are ready to buy chargers. Some are cheap and drity, some are really advanced.
There are dedicated charger ICs

***
If I would design my own one.. it surely would be an advanced one with a microcontroller and switch mode technology. Not only to adjust charging voltage and charging current, but also to discharge the batteries (partly) and to monitor the health state. Also with alarm to change batteries before they are completely dead. And an alarm before they are discharged .. and an undervoltage disconnect for them not to be killed ... and so on.

I personally would not spend my time to build the above charger which wastes a lot of energy into heat ... and has no benefit against simple, cheap, ready to buy ones.
Again: my personal way...
***

But we don´t know why the OP wants to build one instead of buying one.

Klaus

 

[danadakk]

Memory effect lead acid batteries (or lack of it) :

8 Myths and Facts about Lead Acid Batteries | Advanced Battery Systems

Here are 8 myths and facts about Lead Acid Batteries and how to help preserve there battery life.

www.advancedbattery.ca

Do AGM or GEL batteries have a “memory” like ni-cad batteries?

One of the significant disadvantages of nickel-cadmium (ni-cad) batteries is that after shallow discharge cycles, the unused portions of the...

discoverbattery.com

Regards, Dana.