DS1307 & Rechargeable battery

[lats]

ds1307 battery

Hi friends....I'm using DS1307 RTC in a application. For Battery Backup I have attached a small 3.6 volt 60mAH NiCd battery. But the battery discharges & comes in a poor charged condition from the market. Does DS1307 charges the battery attached to it or will I have to charge it sepeartely from 5 volt. If I put a 1N4007 diode in series with 5 volt & battery +ve terminal will that be sufficient for charging the battery.(As I have tried to show in the attached diagram). I have attached the Battery photograph also.

I request you to please reply as soon as possible.

Thanks.

 

[pranam77]

ds1307 battery charge

The DS1307 will not charge any battery connected to its terminals. You'll have to charge the rechargeable battery through an external source as you have mentioned. Rather using a CR2032 3volt Lithium button cell in the place will have life more than a year. Whats the need for a rechargeable battery? Good luck

 

[lats]

5 volt rechargeable battery

Thanks for replying. Actually the same battery I have mentioned has been provided by my client. i also asked him to changeover to CR2032 but he refused. after placing 1n4007 diode (as I have shown indiagram) it will make the charging voltage = 4.3volts, will it solve the problem ? or will i have to place TWO 1N4007 diodes in series which will make the charging voltage = 3.6V, Will this method of charging be OK?

 

[wp100]

ds1307 backup problem

Hi,

Couple of similar things - the DS1340 has an inbuilt trickle charger - but think its only in SMD

According to Maxim this battery should last 11 years without any charge when used with the ds1307

"A BR1225 lithium primary cell is rated at 48mAh. Therefore, (0.048 / 500e) - 9 = 96,000 hours, or 4,000 days (almost 11 years)"

 

[lats]

battery charger in ds1307

In my conditions when the battery is not in a charged condition when installed for the 1st time, will the diodes be ok for charging?

 

[pranam77]

ds1307 batterie

Yes you may use the diodes in series to 5volts for charging. But limit the current by uusing a 22E 0.5 watt resistor in series to the diode. Good luck.

 

[lats]

ds1307

Thanks pranam. For knowledge I want to know how did you calculated this resistor value. & should I use One or TWO diodes in series?

 

[pranam77]

ds1307 + microcontroller + rechargeable battery

Using one 1N4007 diode in series to 5volts will drop it to 4.4V to charge a 3.6 volt battery and any excess current will drain through the resistor. The value is just an practical guess which should work fine. Without the battery and the actual power supply in hand, it is difficult to calculate the precise value. Good luck.

 

[IanP]

cr2032 ds1307 battery charge

[+5V -> 0.7V diode -> 22Ω] configuration can be rather unhealthy for your 60mAh NiCd battery ..
Most NiCd makers suggest a C/50 rate for constant trickle charging ..
Consider something like R≈560Ω ..

Rgds,
IanP

 

[BABESH]

trickle charge and rtc battery

FOR nIMH BATTERIES,
we can leave for ever when the charged at trickle charge c/20, it may take 36 hours to charge a drained batteries.

In your case 60mA/20=3mAmp.
So( 5V - 0.7V diode drop - 3.6V) = 0.7V
use a 240 Ohms as resistor
Diode will protect from reverse conducting to 5V and resitor will limit the charging current.

--Babesh