How to improve 6v sla battery charger?

[SR19]

Hi all,

I need to power up a 5V 3A load with the 6V battery whenever mains(9V adaptor) fails.I have designed this charger circuit with the help of sample schematics available on internet. I have no confidence that this circuit will work or not as i dont knw how to calculate the exact resistor values, so roughly i put 10k.


Battery : TRONTEK 6V 4.5Ah
Charging current : 1.35 Max.-- I kept 0.5A (10% of battery capacity)
Charging voltage : 7.25V to 7.45V


I need your suggestions to improve this design.

Thank you

 

[neddie]

Re: 6v sla battery charger

That seems far more complicated that necessary. For your application a simple TO220 LM1117 (Adjustable) will probably work fine.
Add a small current limit circuit to limit the current to 500mA.
Cheers
Neddie
P.S You should probably put protection diode across the regulator. Cathode at input , anode at output.

 

[Revathysrini]

Re: 6v sla battery charger

@neddie
Does your circuit keep on charging the battery even after get fully charged?

 

[neddie]

Re: 6v sla battery charger

Yes , but if you set the voltage to the float voltage of the battery (about 6.9V) , it's no problem.
The battery will stop drawing current when it charged and it's terminal voltages equal that of the charger.
It will keep the battery charged and won't over charge the battery.

 

[SR19]

Re: 6v sla battery charger

Hi ,
Thanks for your reply. i have modified my circuit as per your suggestions..Pls go thro' the attached schematic..& tell me your suggestions.

Thank you.

 

[neddie]

Re: 6v sla battery charger

Still think it's way to complicated. Do you need LED indication of MAINS/BATTERY?
No need to switch the circuit via a relay. Just connect it directly to the battery.
While power is present the circuit will run off the charger and when mains fails the battery will take over.
Only caveat of this solution is if the battery is flat and the charger can't supply enough to run the circuit AND
charge the battery FAST ENOUGH.

 

[SR19]

Re: 6v sla battery charger

Thanks for your reply. yes , i need to know whether the load is powered by mains or battery.what is the problem with using relay? Shall i use p mosfet ?
i don't want to use the battery power always..is there any other option?

Thank you!

 

[neddie]

Re: 6v sla battery charger

You won't be using the battery always , the charger will deliver the current when needed.
If you need led indication , then you can use the LED circuits as you have them , but you don't need the 5V regulator , unless it is powering something not shown. Just connect the +5v , going to the mains monitoring led to the input of the 1117.

 

[SR19]

Re: 6v sla battery charger

Does battery takes much time to get fully charged with float voltage?
As you said, charger can provide supply to battery only, not to the load when the battery is down.so that the load is not powered until battery get charged?
if so , how can i overcome this problem?

 

[neddie]

Re: 6v sla battery charger

It all depends on you charger capacity.If it can supply enough current to charge the battery and run you circuit , not problem.
In all likelihood it won't be a problem at all.

 

[SR19]

Re: 6v sla battery charger

Hi neddie,

Thanks for your help.