Portable stereo battery help

Shawry

Member
2013-02-13 1:58 am
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
 
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.

_______________________________________________________Rick.......
 

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Shawry

Member
2013-02-13 1:58 am

Shawry

Member
2013-02-13 1:58 am
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