Prob with RTC Backup Battery.

[vdharan]

Hello,
Iam using PCF 8583P rtc from Philips. Iam interfacing it with PIC18F452. Iam using a 3.6V Ni-Cd Battery as RTC backup Battery when the system powersupply is off.
When there is system power (+5V) the Ni-cd battery is charged.

My problem is the Backup Battery Drains off too fast with in 30 hrs and the time is lost.

I have attached the circuit that iam using. I dont know where Iam going wrong.

Can any one give me a suggestion to overcome this problem.

Thankyou.

Regards,
vdharan

 

[happy2005]

I think the resistor 2.7k is very big, thus voltage drop on it will be much more. So the battery voltage can not efeciently supply to the rtc. I couldn't find rtc datasheet. But i recommend you that read the datasheet of rtc carefully about connecting backup battery.
For a quik solution for this circuit, you can connect a reverse diode parallel to 2.7k to decrease voltage drop ~0.7V.

 

[prinsloo]

Why not try a supercap capacitor?

 

[vdharan]

Yes Now i have removed the resistor. also I have connected the 33pf to the battery so that it will also be powered when there is no supply. Iam testing it now by charging the battery and switching off the system. will come to know about the battery capacity after few days.