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Author Topic: Automatic Switching to Battery on Power Failure  (Read 671 times)
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Hi, I want my arduino and gsm shield to be powered even on power failure. I have one 12V 3A acdc adaptor and 6V 4.5 AH lead acid battery. I'm thinking of using a relay or a diode. which one is better? I already have a 1N5822 schotkky diode for lower voltage drop.

Here is the schematic. The LED represents the arduino and gsm shield.

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I like the diodes for simplicity. The voltage gets reduced to 3.3V for the shield anyway?
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I thought of that too but with the diode it is still draining a very little ampere on the battery even when not in use. Do you think its okay? yes, the gsm shield has on board regulator.
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How can it drain when the diode is reverse biased by the 12V source?
You can also add a battery trickle charger to keep it topped off.
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Oh sorry my bad. How to add it? Do you have some sample circuit?
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I've not done anything with charging SLA batteries. I would recommend a commercial unit such as this
http://www.batterystuff.com/battery-chargers/6-volt/UPG6.html
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Charging sla's aren't that bad, they are pretty robust(I toture them often with electrically abusive experiments), probably the most effecient way would be a mosfet, a regular diode would only be worth it at low currents, a germanium diode is better but still has current limitations(as well as heat)
Basically for that size battery you will want to charge it @.3-1amp constant current untill it reaches close to 13.8, then you have it constant voltage @13.8
Easiest way is to use a lm317 although @1amp you will need a heatsink
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Those levels sound kind of high for a 6V 4.5 AH lead acid battery.
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Oh wow missed that, thought it was 12v battery,
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I think i already have one. Its this one. http://www.sulit.com.ph/index.php/view+classifieds/id/4771722/Sealed+Lead+Acid+Charger+battery+12v+6v+battery+charger

so i can connect it to my circuit the whole time? no overcharge?
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I believe so.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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