How to get 12V-3 amp from 18V-3 amp transformer ?

Discussion in 'General Electronics Chat' started by venkee, Nov 12, 2010.

1. venkee Thread Starter New Member

Nov 12, 2010
4
0
Hi,

I have a 18V-3 amp transformer and I want to get 12 V - 3 amp for an audio amp circuit from this. Is there a simple way to do it or is it better to get a new transformer ( in case the conversion is complicated) ?
[ I am a newbie in electronics and I have been doing only simple circuits, including connecting such circuits to a microcontroller board... ]
Venkee.

2. t06afre AAC Fanatic!

May 11, 2009
5,939
1,222
From you description You want to get 12 volt, 3 amp DC from your transformer. Hmm I am not sure that will be so wise. Take a look here

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3. Audioguru New Member

Dec 20, 2007
9,411
896
A stereo car amplifier using bridged amplifier ICs and 4 ohm speakers produces 14W per channel at clipping when the car battery is 13.6V. Each amplifier produces about 8W of heat so the total power from the battery is about 44W. Then the DC current is 44/13.6= 3.2A when the amplifier is playing as loud as it goes when just barely clipping.
When the power supply is only 12VDC then the power from the amplifiers is less, about 10W per channel at clipping.

4. t06afre AAC Fanatic!

May 11, 2009
5,939
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What are you connecting to your power supply. Does the output need to be regulated? Provide more deatils and we may help better and faster

5. iONic AAC Fanatic!

Nov 16, 2007
1,422
68
The question is, was the measurement AC or DC from this 18V, 3A Transformer?

6. nomurphy AAC Fanatic!

Aug 8, 2005
567
12
Here's something coincidental: if the xfmr has a center-tap, then the 18VAC can be split into two 9VAC lines by grounding the center-tap. Using a full-wave bridge rectifier and appropriate sized filter caps, you will get an output of approximately +12VDC and -12VDC @ 3A total. Now you have a split supply with which to make a decent 10W/Ch stereo amp using 8 ohm speakers.

7. Audioguru New Member

Dec 20, 2007
9,411
896
No.
10W into 8 ohms is 25.3V p-p. An LM1875 amplifier (and many others) will need plus and minus 15V supplies to produce 10W into 8 ohms at clipping.

Your 9V-0-9V transformer will produce a supply that is only plus and minus 11.7V then the LM1875 amplifier produces only 6W into 8 ohms at clipping.

8. venkee Thread Starter New Member

Nov 12, 2010
4
0
WOW ! So many knowledgeable folks responding to a newbie question !!
Thanks a lot to all of you.
---------------------------------

As per the meagre info available with the (readymade amplifier ) board,
it requires 12V - 3 amp DC.

Looks like, as per @t06afre, if it is not a wise thing to do, I'll get a new trasnsformer ( 12V, 3amp).

Venkee.