Connect with us

Help with a battery / charging circuit (can i bypass the battery?)

Discussion in 'Power Electronics' started by Tom lakovic, Apr 2, 2017.

Scroll to continue with content
  1. Tom lakovic

    Tom lakovic

    5
    0
    Jun 6, 2014
    Hi Guys. So I have a project (too wacky to describe in this space) :) that i need help with.

    Part of it is a hacked into portable speaker system... one those jambox type look alikes, that is charged by usb and plays for about 8 hours on battery. For my wacky project i have it embedded in a case where i can't get at it easily and just want to leave it on main power USB the whole time (without a battery even). Problem is when I switch off the main power for too long, the speaker's internal battery goes low and then the thing starts beeping like crazy.

    I *thought* that the simplest thing would be to unplug its battery's 2 prong molex type connector and run it like that (off USB power). When USB 5v is present, it should work (i thought wrongly), and when it's not, it's good and off and battery dead, and therefore no chance of incessant beeping.

    BUT it doesn't work that way does it. I believe the USB power must only be there to charge the little batteries. (via the same 2 prong connector), but me unplugging the battery side of that circuit disables the whole freakin thing. so obviously i can't leave that 2 prong connector unpluged.

    SO... the question: in order to close the circuit i need to plug it back into the battery connector and i don't want to. Which leads me to think: i should short the connector. But with what? a wire? a resister (value?) or a transistor?

    This is low voltage stuff guys, and LOW value, no danger here.
    so I am looking for simple macgyver hack to try, not etching a circuit or flashing new firmware if you follow me? just a kind of: if we were stuck on an island, what and that was the way to radio home, and there was no battery but there was a usb outlet on this island ;) then what would you short that battery connector with? resistor? wire? or transistor? and if so what value should i try.

    Thanks
    Tom.
     
  2. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    A charged battery can supply much more power than a 5V USB connection so maybe the speaker system cannot be powered from USB.
    You and we do not know what the battery voltage is (probably less than 5V) so shorting the 5V USB connector to the battery wire with the battery disconnected might damage the amplifier.

    1) What chemistry is the battery? Ni-Cad? Ni-MH? Lithium Ion?
    2) How many cells or what is its voltage?
     
  3. Tom lakovic

    Tom lakovic

    5
    0
    Jun 6, 2014
    Good point(s)! very good. Doh.

    Bat. was unlabeled, but i'll put it on a meter and post what I find today.
     
  4. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    It is extremely important to know details about the battery:
    1) Its chemistry. A Lithium battery can explode or catch on fire if it is charged or discharged wrong. There are two different lithium battery types each with its own voltage ratings.
    2) How many cell in it.
    Fully charge the battery then measure its voltage.
     
  5. Tom lakovic

    Tom lakovic

    5
    0
    Jun 6, 2014
    Okay measured battery at 6v detached. and 5.5v under load, and so felt confident jumping the battery connection, and voila, it works with USB power, "tricking" the charge circuit. For now anyway.
     
  6. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    Maybe the charging circuit boosts the USB 5V to maybe 7V so that the battery charges to 6V or more.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-