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Battery backup

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maxmanclive

New Member
Hi
I need some help! With my project
I have a 12 volt feed from a Vehicle battery that I have fitted with a Regulator Adapter, Step-Down to 4.5 volts, what I need is to run a battery pack of 3 AA batteries that are only used if the main supply is disconnected.im not sure weather to use a relay,
Any help will be appreciated.
Cheers
Clive
 

ericgibbs

Well-Known Member
Most Helpful Member
maxmanclive said:
Hi
I need some help! With my project
I have a 12 volt feed from a Vehicle battery that I have fitted with a Regulator Adapter, Step-Down to 4.5 volts, what I need is to run a battery pack of 3 AA batteries that are only used if the main supply is disconnected.im not sure weather to use a relay,
Any help will be appreciated.
Cheers
Clive
hi,
Relay circuit, contact rating to suit equipment current.

If the equipment can tolerate a approx 0.7V drop, you could use diodes, shown in Red, in instead of the relay.

Use diode current rating to suit current drawn by equipment.
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Gayan Soyza said:
Hi! Clive can do that with a SINGLE diode.
A single diode is dependent on the incoming power supply having reverse blocking, and as we don't have a circuit of that PSU you can only use two diodes to make sure it works correctly.
 

maxmanclive

New Member
Hi
Thanks for your replies,im a bit of a novice at this’but learning fast’
Is this what you mean about the Diodes and are they in the right place, or is this not right at all, I was wondering if the 3AA Batteries would be getting used as well as the main supply ( would they be going flat as if they were being used).
Thanks again
Clive
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
That's right, the main supply needs to be a little higher voltage than the battery supply, so that power is drawn from the main supply - as the main supply drops lower, the battery takes over.
 

maxmanclive

New Member
Hi
Just one more Question...
If the Main supply is a constant 4.5 volts and the battery backup is slightly higher, does this mean that that the appliance will run off the Battery Backup untill it drops below the fixed main supply, then if' the main supply is stoped the battery will take over untill the main is reconnected...
Thanks
Clive
 

Nigel Goodwin

Super Moderator
Most Helpful Member
maxmanclive said:
Hi
Just one more Question...
If the Main supply is a constant 4.5 volts and the battery backup is slightly higher, does this mean that that the appliance will run off the Battery Backup untill it drops below the fixed main supply, then if' the main supply is stoped the battery will take over untill the main is reconnected...
Yes it does!.
 

maxmanclive

New Member
Thanks everybody, youv'e all been a big help
just got to get on a make it now..i know where to go now for good advice
Thanks
Clive
 
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