ChronoDot RTC Backup Battery Consumption Rate

by owendelong on Mon Feb 27, 2012 2:09 pm

Not sure if this belongs in this forum, but it's my best guess...

I purchased one of your ChronoDot RTC modules.

How long should it operate on battery before the battery voltage drops below
the expected nominal voltage of 2.7v?

Is 2.7v a reasonable anticipated voltage level on the BAT pin as detected by
the Arduino Analog input?

I'm asking because I'm now on my second 1632 and it is now reporting 2.5v.

I'm measuring the voltage by connecting the BAT pin on the ChronoDot
directly to pin 15 on my Arduino Mega 2560.

The readout is based essentially on this (it's part of a much larger
application):

setup()
{
pinMode(15, INPUT);
digitalWrite(15, LOW);
}

loop()
{
int vlvl;
vlvl = analogRead(15);
Serial.print("Voltage: ");
Serial.print((float)(vlvl*5/1024));
}

Should I be using a lower discharge-detection battery value than 2.7v? Is
2.5v reasonable?
The Chronodot has probably had a total of ≤10 hours run time without Vcc
since installing this battery.
The previous battery also lasted about 10 hours of non-Vcc time before
dropping below 2.7v.

This seems like an awfully fast drain of a backup battery for an RTC.

Any thoughts/information greatly appreciated.

I wish you guys made a 1672-based clock. Then again, I wish Maxim made a
hyper-accurate module like the one ChronoDot is based on, but, in a 32-bit
counter instead of BCD. (My application is setting the clock from internet
when available, so, all time storage and manipulation is seconds-since-epoch
(midnight Jan. 1 1970, UTC) and only the display is in human-readable
time/date format. Having to convert the ChronoDot back and forth is a bit of
a pain.
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Re: ChronoDot RTC Backup Battery Consumption Rate

by adafruit_support_bill on Mon Feb 27, 2012 2:49 pm

MaceTech are the designers of the ChronoDot. They estimate battery life in excess of 8 years: http://docs.macetech.com/doku.php/chronodot

What circuit are you using to monitor the battery level? Make sure that it is not inadvertently draining it.
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Re: ChronoDot RTC Backup Battery Consumption Rate

by macegr on Tue Feb 28, 2012 2:00 am

I'll second the warning that the voltage reading circuit may be draining the battery.

You'll also want to make extra sure that the ChronoDot is actually getting VCC. "Well it works" you might say, but remember that the DS3231 will actually communicate via I2C while on backup battery only. That will drain the battery faster.

There are also some settings that will output the square wave signal while on backup power. None of those settings are enabled in example code.

I have ChronoDots a couple years old, running all that time with no VCC and the backup battery is still good.

Finally, just use the Arduino Time library. Anything in there designed to work with the DS1307 will work with the DS3231. It already handles communication with the RTC, syncs at an interval you define, and time is handled internally as an Jan 1 1970 epoch timestamp. Look here for a project I just did with the Time library: http://www.macetech.com/blog/node/115
macetech LLC - http://www.macetech.com
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Re: ChronoDot RTC Backup Battery Consumption Rate

by 02.anand.m on Tue Feb 28, 2012 8:51 am

hii guys..i also got a problem working with ds1307...in my case i got ds1307 working with atmega 8 and i get the correct time display..but when i use atmega 168...it shows 0:0:0...time is not getting display.... my hardware is working perfect.......can anyone help me with this????
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Re: ChronoDot RTC Backup Battery Consumption Rate

by adafruit on Tue Feb 28, 2012 10:58 am

02.anand.m wrote:hii guys..i also got a problem working with ds1307...in my case i got ds1307 working with atmega 8 and i get the correct time display..but when i use atmega 168...it shows 0:0:0...time is not getting display.... my hardware is working perfect.......can anyone help me with this????


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