Lead Acid Battery Charging Circuit for 24V

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Hi all,
I have to charge a 24V 12Ah Lead Acid battery with combination of two 12V batteries in series.

I have selected UC3906 charging IC for to charge the battery.

I gone through the application note of UC3906, https://asmith.id.au/files/uc3906-battery-charger.pdf
in that they had given, there is a three state of charging. Bulk Charge State, Over State, Float state.


I have constructed this circuit for to charge the battery. by this circuit battery is getting charge, but i couldnt identify the state of the charge. for this they given the formulas to calculate. in the formula, i couldnt get the vref value, from where i can take this vref.
And they mentioned, when the battery get the full charge, Over charge indication pin get low. but i couldnt get that things.
and also please explain how to identify the charging rate of the battery in this circuit.

And i give the resistor details of the circuit for your ref,
Ra = 200K
Rb = 27K
Rc = 47K
Rd = 400K
Rt = 330E
Rs = 0.5E
Source Resistor at 15th Pin - 470E

Please guide me regard the charging circuit and its calculation.
 

Hi,

I didn't go through the whole application note:
But it says:
As the battery is charged its voltage will
rise; when the scaled battery voltage at PIN 13, the invert-
ing input to the sense comparator, reaches 0.95Vref the
sense comparator output will go low.
Click to expand...

Hint: use the pdf viewer's search on "ref"

Klaus
 


The Vref is 2.3V, you can see it on the block diagram in the PDF.
 

Thanks Vbase,
Ok. for various input supply, that vref 2.3v will be same or it will be different for different supplies.

- - - Updated - - -

KlausST said:
Hi,

I didn't go through the whole application note:
But it says:


Hint: use the pdf viewer's search on "ref"

Klaus
Click to expand...

Thanks Klaus,
I couldnt get that over charge indication to low.
I monitoring the battery voltage for every hour, it has been increasing by 0.4V/hr. it keep on going upto 24.8V from 22.0V. after that there is no more charging, during this period, it has to be change in the state of the OC indication pin, but no response in the pin.
 

The Vref is a stable voltage. It can vary with temperature and from one chip to another from 2.3 to 2.4. If you cannot get the right resistors add a trimmer in series to Ra. Fully charged batt is 28.4V. This voltage depends on the charge current and the size of the batt. With a trimmer you can test if the over charge works and at what voltage. Using the trimmer will help you to study the circuit operation like some do with a simulator.
 

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