battery backup plan

[MrDEB]

Building a clock and decided to include a battery backup.
I wanted a MOSFET, but a small DPDT relay is perhaps easier.

here is my schematic that I am consifering.













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[aliarifat794]

Looks OK. However, it is better to simulate the circuit.

 

[Nigel Goodwin]

Jesus, all you need is a single diode, or at most two - but the second isn't usually needed (as the bridge rectifier usually serves that purpose).

 

[Diver300]

It doesn't look right that the relay needs to be energised to connect the backup battery.

 

[MrDEB]

it is an N.Closed relay unless I have it wrong?

 

[crutschow]

You want the 5V through the NO contacts, and the NC contacts to the battery backup.
You appear to have that opposite.

 

[Pommie]

Why not just backup the timekeeping circuit like most normal people do. Your battery will go flat very quickly (assuming it's powering the LEDs) and you won't realise your power has gone off - or will you?

Mike.

 

[For The Popcorn]

Why not just backup the timekeeping circuit like most normal people do. Your battery will go flat very quickly (assuming it's powering the LEDs) and you won't realise your power has gone off - or will you?

Mike.

If you think way back to the start of this project (which has spanned several threads), the use of an RTC chip is somewhat beyond MrDEB's abilities. He's counting clock cycles in the micro, which makes battery backup somewhat more complex.

It looks like MrDEB is planning on using a 9 volt battery. An alkaline 9 volt battery supplying 33mA will last less than 24 hours a day based on an hour use each day.

 

[MrDEB]

as of today 11/14/24 the battery backup is no longer in the plan