5 volt dc power supply with battery backup

[rizzy_dascal]

Hi,

I am looking for a circuit of a 5 vollt DC power supply that also charges a sealed 12 volt lead acid battery which will take over if the mains fails, the closest I can find is a burglar alarm power supply but it is 12 volt dc and not 5 volt dc.

Regards
Rizzy

 

[Sunny55]

Hi,

I am looking for a circuit of a 5 vollt DC power supply that also charges a sealed 12 volt lead acid battery which will take over if the mains fails, the closest I can find is a burglar alarm power supply but it is 12 volt dc and not 5 volt dc.

Regards
Rizzy

Hi, what about using solar power? You can get a 16V solar panel to charge the battery via a charge controller. From the battery, you can use an LM7805 IC that gives you 5VDC from the 12VDC battery. Hope that answer your question.

 

[rizzy_dascal]

Hi Sunny,

The circuit I am building is to alert me to a mains power failure, so I need to charge the battery from the mains voltage so that I know it is definitely going to work, thanks for the reply though...

cheers
Acestu

 

[Sunny55]

Hi Sunny,

The circuit I am building is to alert me to a mains power failure, so I need to charge the battery from the mains voltage so that I know it is definitely going to work, thanks for the reply though...

cheers
Acestu

Hi, the idea is actually similar to an emergency light whereby the light is charged and when power is down, it starts running. However, you will need around 14Vdc to charge up a 12Vdc battery.

What i suggest is that you use an AC to DC converter circuit to step down mains voltage(110V or 240V) to 14Vdc. The 14Vdc is given to the battery(with a charge controller in between 14VDC and battery for safety) and another IC(14vdc to 5vdc step down IC) to get your 5Vdc. Just check the IC's datasheet to see whats the max voltage it can take in as i am not sure.

Just be careful with the project and all the best !

 

[BradtheRad]

It sounds as though you want to construct a project which consists of three functions:

1) Convert mains AC to 5 VDC.

2) Step 5V up to approximately 15 V, to charge a 12V battery.

3) Stop charging the battery when it is full. Resume charging when its voltage drops. (Charging may be a trickle rate.)

Is this correct?

 

[rizzy_dascal]

Hi Brad, sorry I have been so long replying I have been ill,

Yes that is exactly what I need to do, do you have a schematic or any info for that please ?

thanks
Rizzy

 

[BradtheRad]

It is easier to make a 12V DC supply, and step it down to 5V, rather than vice versa.



If you really want to have the 5V supply first, then use a 6V transformer. You'll need to make or obtain a boost converter, which can step up 5V to 15V.

The battery charger does not need to supply a lot of current. It can take a long time to charge the battery.

The 12V battery should not receive a charge after it is full. Your charger should turn off when it has risen to 14.4V. Then it should wait until the battery is down to 12.4 or 12.5 V before it turns on again.