# Simple 12v 3amp power supply

Discussion in 'Electronics Homework Help' started by Suny, Sep 20, 2016.

1. ### Suny

7
1
Sep 20, 2016
I have a 12v 3 amp transformer.how can I supply 3 amp power?? Pls give a simplest circuit.

2. ### duke37

5,364
769
Jan 9, 2011
Just connect to the transformer output. You will get 12V AC at up to 3A, the maximum power will be 12*3 = 36W.
What will be using the power?

3. ### Suny

7
1
Sep 20, 2016
I need dc power for charge my 12v 9AH battery.

4. ### duke37

5,364
769
Jan 9, 2011
To change AC to DC you need a rectifier. The best solution is to use a bridge which can be made from four diodes or a bridge rectifier which is a square block with four connections, two for AC and positive a negative output. You may need a heat sink if running at the full 3A.

To limit the current to a safe level, you could place a bulb in series. I have a tame mechanic friend who saves me headlight bulbs which have one broken filament. An ampere meter whould be advantageous as would a voltmeter. Car alternators are usually set to limit charge to 13.8 to 14V for lead/acid batteries.

5. ### Suny

7
1
Sep 20, 2016
I also need a full charge mediam and low charge indicator. Would u help me?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,418
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Jan 21, 2010
You won't get 3A DC unless you use a switch mode regulator. With a linear regulator the max current without overloading the transformer is a little over 2A.

7. ### davennModerator

13,671
1,892
Sep 5, 2009
what sort of battery ? lead acid, sealed lead acid, something else ?

different batteries require different charging methods

8. ### Suny

7
1
Sep 20, 2016
Lead acid battery

davenn likes this.
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