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Getting correct wattage from lead-acid battery

  1. Mar 7, 2013 #1

    So I have a question that I feel is best suited for people who know much about electricity and circuits. I have a 12V 7Ah sealed lead-acid battery (here, FYI http://www.parts-express.com/pe/showdetl.cfm?Partnumber=140-366).

    I also have a small stereo amplifier, 12VDC 2A, that is 15W/channel (2 channels, found here: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-385).

    Finally, I have a simple 12V USB adapter, the kind for a car's cigarette lighter (here: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=125-362).

    I know that this circuit board works well with this battery, but I'd like to charge my phone at the same time as I listen to music! Is it possible (and safe), to wire the battery to the stereo amplifier and to the 12V adapter in parallel to power both devices? Are there any problems I should consider?

    Thanks for your comments!
  2. jcsd
  3. Mar 8, 2013 #2

    jim hardy

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    no takers yet?

    should work fine, from looking at what datasheets i could find..

    Stereo board appears to have a filter capacitor
    http://www.daytonaudio.com/media/resources/300-385-dayton-audio-dta-2-manual-43360.pdf [Broken]
    so you shouldn't need one external. If it "motorboats" try a large capacitor right across the battery; probably it won't.

    and the phone charger doesn't say a thing about its internals.. so dont plug the phone into the stereo with another cable....

    There's a very remote chance the phone charger will upset the stereo y switching noise. If so you'll have to add filtering, but i doubt it'll happen.

    Phone charger can output two amps so it might draw one amp.
    Stereo will draw small fraction of an amp unless you use it for one of those earth-shaker car stereos. If it approaches an amp i'd be surprised.
    Last edited by a moderator: May 6, 2017
  4. Mar 8, 2013 #3


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    Way off topic here.

    I knew exactly what you meant but hadn't heard it for a long time, so I did a search and this is all I could find; electrically that is.

  5. Mar 9, 2013 #4

    jim hardy

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    Thanks Don i'm getting old and forget everybody wasn't messing with electronics fifty years ago (nice article there from 1927 !)

    "Motorboating" sometimes happens when a battery powered audio amp is playing loud material with a lot of low frequency content. A big bass passage demands a large "gulp" of current which may briefly overload the battery. So battery voltage sags and the amp distorts. It can cause a sound resembling an inboard motorboar exhaust that's not quite under water 'burbling'. Nowdays nearly everybody has outboards so i guess the term is outdated.

    old jim
  6. Mar 9, 2013 #5
    Assuming you aren't operating the stereo amp at max volume, it's going to consume much less than the rated 2 amps, so battery life should be pretty good. Of course, besides the previously mentioned issues, the battery will discharge faster with each additional load you connect.
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