Normal/Alternative DC uninterruptable power supply with battery back lighting circuit

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Hi guys.

I need some help designing a Normal/Alternate DC uninterruptable power supply with battery back-up to illuminate a 14v lighting circuit.

I will be using Locktronics to build the circuit and it needs to be as simple as possible.

SPECS: Normal Alternative supplies to be rated @ 14v
Battery back-up yo be 12v
supply available lamps are to be red LED's
supply in use lamp to be red for N/A supply and green for battery supply

I'm not really to sure where to start as my electronics knowledge is very basic.

I am thinking of using relays to switch between the supplies as one drops out or drops below 20% of its required power.

Also using transistors to act a a switch so if the power drops and I don't have 0.6 volts on the base then that leg of the circuit will be closed.

I have a basic idea but any help or assistance that can be offered would be greatly appreciated.
 

See this :


Just ensure battery voltage to be under voltage of power supply, and done. No need for transistors and microcontrollers for this.

This is simple circuit.
 
Good idea about 1 relay needed for the switching to batt.
now all u need is a charger supply that will charge your batt from the supply u using currently for the leds.
 

Thank you tpetar.

Part of the brief I've been given is that it must switch from normal to alternate supply if power drops below 80% power and then again to battery backup if the second supply again drops by more than 20%.

I can't seem to get my head around it and as I have the least electronics experience in our group I seem to have been lumbered with the more difficult project.

I have relays, caps, transistors, resistors, led's and diodes in the toolbox I have been given so I'm guessing I can get a solution using just these items.

I have searched for basic circuit diagrams that fit my needs and that I can easily understand but I have so far come up with nothing.
 

Like example :
over/under voltage cut out circuit diagram

You must adjust voltages, this is just like one example of principe.

Consider relay current consuption from batteries! Better use impulse relay or mosfet. Or use other contacts on relay, when on battery source relay coil is not energized.
 
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Unfortunately I'm not sure what any of that means. I have only a rudimentry understanding of electronics. Is there any UPS circuits that would work for my situation just using relays and transistors. I feel I'm a little out of my league with this project and don't really know where to begin.
 

Hello mrnoob
u need to work a little harder to stop being newbie.
just google what u need ... batt charger circuit diagram and u will get the link about .
just go 1 by 1 thats what i do .
there are miilons of diagram on the internet.
Battery Charger Circuits | CircuitDiagram.Org
 

variation of tpetar s circuit
normally supply will energize the relay and contact no will supply the load .
when pwr falls the relay goes nc and batt will supply.
resistor and diode will trickle charge the batt all the time.
 
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    MRnOOb

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Good idea! There is no need for transistors and microcontrollers. You just need a charger that can provide AC power to your battery.
 

"drops below 20% of its required power." We all forgot about that
 

Hi everyone,
my circuit is suppose to be uninterruptable power supply but whenever I turn off the supply, my PIC restart. The swtiching in the relay is not fast enough to prevent my PIC from restart.

My question is what modification can I do to my circuit for it to be uninterruptable. Or is it that nothing can be done to make it uninterruptable.
Any idea?



thanks in advance!
 

To prevent the PIC from restarting, use a bulk capacitor between the 5V and ground (pins 1 and 2 of the connector). Try with 2200uF and see if that's enough. If not, you can increase it.

Instead of relay, use solid-state switching with transistors to make the switching really quick and to avoid problems associated with mechanical switch such as relay.

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I know this is late, but it might help others who stumble upon this thread.
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Hope this helps.
Tahmid.
 

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