Relay switching time control using capacitor

[Naveed Ahmed]

Hello dears!

I have designed Energy meter using ATMEGA32 MCU. For powering it, i have used separate power supply. When power is loss, MCU is turned off and all parameters are erased.

So, i have used a separate battery, which is used incase of power failure. The switching between power supply and battery is done using 5 pin SPDT relay using following config...

NO------Power supply
NC------Battery
C--------Output given to my circuit

When power is switched from battery to power supply, there is no problem . But when power is switched from power supply to the battery then MCU restarts, and all the static RAM parameters are lost

my circuit current consumption is 300mA at 5V.

I think i have to use Farad capacitor. so that it can maintain power for some time when relay switches???

I have 1F capacitor (5.5V) available at market.



Thank you...

Suggestions and ideas plz...........



Regards

Naveed Khowaja

 

[cyberrat]

power it always from the battery, no relay.

Just charge the battery when mains is on, use diodes to isolate charger from battery.

That way you do not lose anything except for when the battery goes flat.

 

[Naveed Ahmed]

Thanks dear.

But will it be a problem when we switch from Power supply to the battery??