Why is my RTC loosing time?

Microcontrolled

I have a DS1302 RTC (Real Time Clock) with the proper Xtal and low noise connections. However, it has lost ~20 seconds since I set it last night. It has been running off the backup battery overnight. I know that it looses some time, but not this much! The parts I am using are here:
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&productId=176778&catalogId=10001&freeText=176778&app.products.maxperpage=15&storeId=10001&search_type=jamecoall&ddkey=http:StoreCatalogDrillDownView

And here:
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&productId=325244&catalogId=10001&freeText=325244&app.products.maxperpage=15&storeId=10001&search_type=all&ddkey=http:StoreCatalogDrillDownView

Phil Pilgrim (PhiPi)

According to its datasheet, the DS1302 is designed for a 6pF crystal. The crystal you're using is spec'd at 12.5pF. That might make a difference. Also, what's the temperature environment surrounding your RTC? That can make a difference, too.

-Phil

erco

Time definitely goes by faster as you get older...

sam_sam_sam

This work real well keep time
DS32kHz 32.768kHz Temperature-Compensated Crystal Oscillator

Tis very inportant follow what it has here

Figure 6

shows one circuit that

can be used to reduce the current consumption of a DS32kHz and an RTC. The values of R1 and C1 may vary

depending on the RTC used. However, values of 1.0M

Ω and 100pF are recommended as a starting point. R2 is
used to shift the input waveform to the proper level. The recommended value for R2 is 33kΩ.

I had adj the value of R2 a little bit for it to keep the time right on the mark

http://datasheets.maxim-ic.com/en/ds/DS32kHz.pdf

I hope this helps