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Boombox wiring (Noob question)

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  • Boombox wiring (Noob question)

    Hi Guys,
    I'm building a small boombox for my daughter. I'd like to power it with a drill battery and a power supply.
    From what I understand it's ok to put the power supply and battery in parallel with a diode in between and everything should work fine.
    If I connect them as in the wiring am I doing the right thing?
    I want to be able to power the amp with battery alone, without battery and in case charge the battery while listening to music.
    I already measured the original battery charger and the battery output, those are 21V and 19V so I'm getting a 21V 2A battery charger to plug in the wall.

    Amp: TPA3110D2 2.1
    Battery: 20V Ferrex Activ Energy (Aldi)
    Power supply: 21V 2A
    Diode: 1N5822 SCHOTTKY DIODE 3AMP? (Is this the right one?)

    Thanks guys and sorry for the noob questions!


    Click image for larger version

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  • #2
    It looks fine to me - someone more knowledgeable will be along shortly to chime-in.

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    • #3
      Not me, but I did build a nice boombox using one of PE's ammo can kits and an oak cabinet. PE has several kits with 18650 batteries and power brick chargers, 2.0 and 2.1.

      https://www.parts-express.com/speake...type/Bluetooth

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      • #4
        Hi Guys, thanks for the answers!

        @Steeve Lee: Thanks I'll go on and try it out until someone tells me differently!
        @DJG: I've seen them, but I already have all components and a drill battery should bea lot easier to manage than a simple battery pack as it already have all the electronics embedded. Easier if you know how!!!

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        • #5
          This is NOT a good idea... You're feeding the power supply directly to the battery via the diode, which could result in significant damage to the battery (fire/explosion). Lithium batteries can be easily damaged if not charged properly. A power supply and a charger for lithium batteries are NOT the same thing. Lithium batteries require a very precise CC/CV charge profile (constant current/constant voltage).

          You need another diode to prevent the power supply feeding unregulated/uncontrolled power into the battery. This creates a diode "or" which allows the battery OR the power supply to provide power. I've taken your drawing and added the second diode. Also, just a nit-pick on my part, but where you've drawn the power coming in to a typical amplifier symbol is the signal input. I re-drew where the power lines typically feed in.

          Click image for larger version

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          • #6
            Depends where you are in the world, maybe instead of that you could try a Dayton Audio LBB battery board and head down to your local vape store and grab a couple of LG, Samsung or Sony 18650 cells. That would give you 12v (3*18640) but I believe they may have a 5 cell board as well. It has the charging circuit on the LBB's where the KAB ones don't (from memory).

            Food for thought as originally I was thinking using a drill battery and slot.it and out to charge it, but went down a different path.

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            • #7
              Thanks all, and especially thanks for saving my home from fire! :-)
              I'll see if I can tear down a charger and eventually use the pcb to charge the battery, but for the moment I'll stuck with the dual diode solution!
              Cheers!

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