making a power supply

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Metal Frost

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hello,

I have an very nice and compact speaker set. I want to make the speakers portable, but the problem is that they need a AC-DC power supply.

Now I was wondering if I could replace the AC-DC adaptor with a DC-power supply.
The speakers need 12V & 1000mA.

I found some batteries that produce what I need, but is there a possibility that I can use a single 1.5V 2450mAh NiMH rechargeable battery, that can produce what I need through a circuit?

I it is possible, the power supply can stay as small as possible, because a 12V battery is heavy and a bit on the large side for a portable speaker set.

Can anyone help me?

Thanks

Metal Frost
 
It's not possible to power the speakers from a single AA battery.

You need to connect at least eight in series to power the speakers properly.

There are circuits that boost voltage but they also suck more current from the battery so a single AA battery wouldn't last for five minutes.
 
Ok, But can I use a boosting circuit and 2 (or max 4) batteries?
I also found that the speakers will work with 9V, so the boosting doesn't has to be so large.

And if that couldn't work, is there an alternative for a large and heavy 12V battery (or 8 single AA batteries)
Something small and not to heavy?
 
How about using eight AAA batteries?

You could use a single 9V battery but it won't last for long. The smaller the battery the shorter the life will be.
 
You forgot to say which amplifier and speaker you have but if the speaker is 8 ohms and the amplifier is single-ended then the power is only 1.5W at clipping if the supply is 12.0V. Then the max current from the 12V power supply is about 225mA.


If the amplifier is bridged then the power into 8 ohms at clipping is about 5W and the max power supply current is about 600mA.

If the amplifier is bridged then the power into 4 ohms at clipping is about 9W and the power supply current is about 1A.

If the amplifier is bridged and has a supply that is only 9V then the power into 4 ohms is only 4.2W and the power supply current is about 700mA.
 
There is an amplifier inside of the speakers.
The speakers self: max power = 2 x 5W and impedance of 4Ohm
The amplifier: max power output = 2 x 4W and impedance of 150 Ohm

Is this amp then bridged or not?
 
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I don't know if your speakers and amplifier is rated in phoney Whats or in real Watts.
Amplifiers drive 4 ohm or 8 ohm speakers, not 150 ohms.

I think each amplifier has a phoney peak output of 4W at 10% distortion into 4 ohms. Then its RMS real power at clipping is only 1.5W into 4 ohms so the amplifiers are not bridged. Both amplifiers produce a total of 3W to the speakers and about 3W of heat so they draw 0.5A from 12V.
 
The speakers will not draw 1A continuously, it'll be the peak current rating.

My guess is that 5W is the peak power, not the RMS power.

150R is probably the amplifier's input impedance.

None of this really matters anyway, you'll need at least either NiMH cells in series to power the speakers. AAA cells will probably do, if you're tight on space. You can buy battery holders which carry four AAA cells and connect them in series.

EDIT:

You can use a booster circuit for four AA batteries but it isn't a very good solution. Any voltage converter will loose some power so you're better of using more smaller batteries. If you really think a voltage converter is the only solution, you can buy converter ICs to do this or even ready made converters but the latter might be expensive. You also have to take into account the size of the converter.
 
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OK, Thanks!

I will probably use some AAA batteries. But does anyone have an idea how long the will survive, if I should use the speakers at their maximum output?
 
It depends on the music.

Some heavy metal or drum 'n' bass will flatten the battery quicker than more something more gentle.
 
Metal Frost said:
OK, Thanks!

I will probably use some AAA batteries. But does anyone have an idea how long the will survive, if I should use the speakers at their maximum output?
Click to expand...

1.5v at 2450 mAh = 3.675 watt hours. So continuously supplying 12W you will get about 18 (3.675/12 x hours) minutes in a perfect world.

In the real world however, battery capacity is rated over longer periods (perhaps 245mA over 10 hours) and will probably only output half it's rated capacity over such a short time period. Also DC-DC converters are not 100% efficient.

All-in-all you can probably expect around 5 minutes, as already suggested by Hero.
 
Gobbledok said:
I would hope an amplifier doesn't have an input impedance of 150R! An amplifiers input impedance is usually around 50K.
Click to expand...

It's probably designed to be connected to a headphone sound card outlet.

I have a pair of amplified speakers which have an input impedance of 8R.

1.5v at 2450 mAh = 3.675 watt hours. So continuously supplying 12W you will get about 18 (3.675/12 x hours) minutes in a perfect world.
Click to expand...
Sorry but it's not a continuous load, the power is continuously changing so you can't calculate it as simply as that.

Play some gentle easy listening classical music and it'll probably last for ages.

Play some thumping hip-hip and it'll last five minutes.
 
Hero999 said:
It's probably designed to be connected to a headphone sound card outlet.

I have a pair of amplified speakers which have an input impedance of 8R.
Click to expand...

Fair enough.



The question says at full power output.
 
The OP doesn't know that when the peaks of music are at the maximum output then the average level is at 10% or less.

An AAA alkaline cell is not 2450mAh. An Energizer cell is 1200mAh with a load of only 25mA and when its voltage has dropped to only 0.8V.
Its voltage drops to 1.2V in one hour when it supplies 0.25W or 220mA continuously.
 
Ok, thank you all!
Because I used AAA cells, there was room for 2 more.
And Hero was right, when I play some classic music, it last for +- 10h
And some heavy metal => 55 min
So when I play heavy metal, I turn the volume down a bit, that way the cells last a bit longer.
 
10 hours listening to classical and under an hour of heavy metal?

Have you got that right?

I'm surprised there is such a difference.

How many AAA cells did you use in the end?
 
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