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Old 13th February 2013, 02:56 AM   #1
Shawry is offline Shawry  Australia
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Default Portable stereo battery help

Alright so I'm looking at building a portable stereo like this.

6x9 speakers portable boom box mp3 dock apple ipod music usb mini amplifier | eBay

The problem I am having is figuring out what size battery to use since battery life is important to me. From what I have found most amps this size( 20+20 watts) use around 5ah does this sound right? So if u have a 20ah 12v battery then I would get about 4 hours use out of it?

I dont see how the eBay item above can have 36 hours of use when It is so small and weighs only 7kg.

Can someone clear this up or me
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Old 13th February 2013, 03:45 AM   #2
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Recall the concept of duty cycle.....An amp isn't going to be drawing a steady current..At regular listening levels the amp will be drawing a shockingly low current load, allowing a total Ah supply of seemingly tiny size.
Back in the mid-eighties I built such an elaborate "portable" "boombox" using A Pioneer cassette head, and a GM120(60WPC) amp...driving a pair of Minimus 7s. Heavy SOB. A very impressive device....dozens would stop to interrogate me & listen.
Inside the wooden box housed a Motorcycle battery. According to the numbers it should have "lasted" half a dozen hours only.........It took about a week to draw it down.
Also, there is a low-voltage limit to where the various devices will shut-down (10.2V?). Take your ammeter & check what values you get & I'd bet you'd be surprised.

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Old 14th February 2013, 05:00 AM   #3
Shawry is offline Shawry  Australia
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alright i am just trying to get an idea of what battery life to expect. any ideas on if i used the following battery and amp?

Battery - eBay Australia: Buy new & used fashion, electronics & home d?r

Amp - eBay Australia: Buy new & used fashion, electronics & home d?r


connect to one 6 by 9 of 110 watts rms
is that enough information to get an accurate idea of battery life assuming it will be at close to full volume?
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Old 14th February 2013, 05:14 AM   #4
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Quote:
Originally Posted by Shawry View Post
connect to one 6 by 9 of 110 watts rms
is that enough information to get an accurate idea of battery life assuming it will be at close to full volume?
Given that the amp is a class A/B amp and not a class D amp. It will run about 2 hours on that battery at near full volume.
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Old 14th February 2013, 07:10 PM   #5
Shawry is offline Shawry  Australia
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Dang I am hoping to get around 10 hours.

Would a 20+20 watt amp make a massive difference in terms of battery life?

Also can any one confirm wether the bellow link is realistic in battery life?

6x9 speakers portable boom box mp3 dock apple ipod music usb mini amplifier | eBay

It has 36 hours of battery and the guy selling them told me they only weigh 7kg, he wasn't keen on discussing what parts he had used.

Thanks for your help
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