# Simple 12v 3amp power supply

#### Suny

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

#### duke37

Jan 9, 2011
5,364
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?

#### Suny

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

#### duke37

Jan 9, 2011
5,364
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.

#### Suny

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

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
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.

#### davenn

Moderator
Sep 5, 2009
14,271
I need dc power for charge my 12v 9AH battery.

what sort of battery ? lead acid, sealed lead acid, something else ?

different batteries require different charging methods

#### Suny

Sep 20, 2016
7
what sort of battery ? lead acid, sealed lead acid, something else ?

different batteries require different charging methods

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