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portable speaker help

Discussion in 'General Electronics Discussion' started by chemacky, Aug 29, 2014.

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  1. chemacky

    chemacky

    3
    0
    Aug 29, 2014
    Hi guys,

    I'm currently in the planning/semi-begun-building stage of my first DIY electronics project, which is in the form of a portable boombox based around the lepai 2020A+ amp and the Sure APT-X Bluetooth 4.0 module (which both run off 12v). Despite searching the entire internet up and down, I just can't seem to make the electrical/power side of the wiring clear in my head. And to be honest, I'm a little worried about burning a house down/killing a battery and would be very grateful for some help.

    I'm looking at incorporating a cig lighter 12v socket for charging accessories like phones/audio players/whatever through a classic car to usb device as the stepdown, as well as a 2.1mm DC jack that can be used to charge the battery via AC mains (240v in Australia) as well as via a small solar panel. I am sort of hoping that I could be playing music and charging accessories while the solar panel or AC mains is plugged in... basically I can have anything plugged in/not plugged in/left overnight by accident and the house wont burn down.

    I have attached a mock wiring diagram that worked in my head, but I really do doubt if this is actually an acceptable circuit. There are also a couple of components I have left off there because I simply wasn't sure where to put them.

    The first is a simple power switch, so that when off nothing can drain the battery. Is this a simple case of wiring in line on the positive lead between the battery and the solar charge controller?

    The second is a small volt/ammeter (http://www.ebay.com.au/itm/251498991739?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) that I would desperately like to use to know both when the battery needs recharging, as well as how much current the amp is drawing. I have absolutely no idea where to begin with this one. The yellow wire is scaring me even though the product hasn't arrived yet! Can anyone help with this?

    Am I at least on the right track?

    I hope you understand my misunderstandings, and are accepting to an enthusiastic novice's questions

    Thanks!
     

    Attached Files:

  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Looks reasonable. Couple of questions.
    1) Do you have a solar charger in mind or are you planning on just connecting the battery to a solar panel?
    2) What is array is this just a direct power connection to the battery.
    3) What is load and why is it not connected to anything?
    4) Will a 2.1 mm jack be able to withstand the amount of current for battery re-charge? What battery is it.

    I don't know whether it's a good idea to have the solar panel and mains charger connected at the same time. If the solar panel it putting out a higher voltage than the charger when in bright sunlight, will this damage the charger by forcing current back the wrong way or will it just draw no current from the charger. I don't know is the answer, you would have to give some details on the charger or PSU you plan to use.

    Looks like your current meter reads up to 10 Amps with a direct connection of the yellow to black, current will be sensed through the black wire. Anything more than this you will need a resistor (1.5 mOhm) to shunt away the remaining current so the unit is not damaged. Then it looks like the yellow is measuring the voltage across the external shunt resistor, it's another volt meter who's reading is converted into a current. We know this because it asks you to not leave this line floating and connect to 0V.

    Adam
     
  3. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Ok I am thinking something along these lines.
    SOLAR.JPG
    The only concern I have is about the power adaptor, we could put another diode in line with it's power lead depending on the type you choose. But if the battery is flat and you plug in the power adaptor and you try to use the amplifier then it could trying and draw too much current from it and possibly damage it. I would put a circuit in that switched out the amp when the battery was charging from the adaptor otherwise to power the amp from this adaptor with a flat battery is going to take some power supply.

    Edit: If the battery charger had current limit, which it should then as long as this is lower than the power adaptors current rating then this should work.

    Just some thoughts
    Adam
     
    Last edited: Aug 29, 2014
  4. chemacky

    chemacky

    3
    0
    Aug 29, 2014
    Thanks so much for the reply!

    I guess I will start with your questions:

    1) I have already bought a solar charge controller (This one: http://www.ebay.com.au/itm/111439015690?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649) Its a 20A charge controller, is this going to be an issue for the small current generated by a small solar panel? I think at max mine is 500mA.

    2) Array is the input for a solar panel on the solar charge controller.

    3) In all honesty I'm not really sure what load is, but from what I can tell, its for lights. The charge controller turns it on once it doesn't detect 'daylight' anymore. I'm quite certain you can have this off completely... and in my mind this makes sense for my application.

    4) I'm not sure, I hope so since i already bought them! Many similar projects seem to use 2.1mm jacks, so I just assumed so. At the moment I have a couple of 6AH 12v SLA btteries, but depending on how much current the amp is drawing at higher volumes I would consider going as high as a 15 or 18AH SLA. Which although I realise will severely detriment the system's 'portability', battery life is also very important to me. I was hoping to charge the system via AC using the amp's current power supply, which form memory, is a 13.2V 5A wall wart. Is this acceptable?

    Sorry, I musn't have been very clear, but I won't be running a solar panel and wall charger at the same time. The solar panel won't be permanently wired in, as its a camping accessory that gets used for other things. I was just planning to use it (wired through the 2.1mm DC jack) to supplement power for long playing sessions sometimes. It will likely mainly be charged using AC mains. I mentioned all this as I was hoping that I could play music and charge accessories while the system is simultaneously plugged in to either the solar panel or AC (but definitely not both). Does that make sense?

    I was sort of hoping that the charge controller was going to take care of all this for me, is that the case?

    Thanks again for your reply, I really appreciate you taking the time to help out!
     
  5. chemacky

    chemacky

    3
    0
    Aug 29, 2014
    I lied sorry, the AC wall adapter for the amp is 13.5v and 3A.
     
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