Battery backup for the BS2p24

Husky X3

I am looking to build a battery backup circuit for a BS2p24 Demo Board that will enable a smooth power transfer in the event of a power outage. Currently, it is powered via a 9V AC adapter-- which will remain its primary source of power. I have been all over the web trying to find something on the subject , since my knowledge of this is very limited. Unfortunately, that didn't take me anywhere.






Any advice or ideas?? One thing: it must operate between 9-6V


THANK YOU.

Post Edited (Husky X3) : 6/25/2006 7:43:02 PM GMT

bennettdan

http://forums.parallax.com/forums/default.aspx?f=5&m=132186
Look at this forum

Husky X3

Also:

I want to know if i can integrate some kind of Zener diode settup into the circiut to regulate the flow of the voltage to the demo board, and thus allow the battery to run in the background with the charger. Should power B lost, the battery would then be able to take over completely without a delay.


{ BATTERY BACK UP }
DEMO BOARD

---

{ WALL CHARGER }



thanx

ccevt

Husky X3,

Attached (I hope!) is a quick sketch of two circuits which should give you a starting point. I have used both techniques sucessfully. The diode OR circuit is simple and works well as long a you allow for the forward drop of the diodes. Rchg is used to trickle charge the battery from the power supply and the value can be calculated by Ohms law based on available voltage, diode drop, battery voltage, and maximum desired charging current. It works as long as the power supply voltage is higher than the battery voltage. The circuit is powered by the heigher of the power supply voltage ---- OR ---- the battery voltage, so that the battery takes over in with power supply failure or brown outs.

The relay circuit requires some power to keep the relay powered but as almost no voltage drop. Select a zener that will allow the relay to drop out at a voltage somewhat above the level that the circuit being powered will remain functional. C1 would typically be about 1000 uF electroltic for light loads, and larger for heavier loads. Select R1 to provide a base current about 1/20th of the relay coil current.

In both cases, the determination of proper values is application dependent, and calculation of appropriate values is left to the student!

Hope this helps

Horace - N1HC