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Powerbank battery level meter?

Discussion in 'Power Electronics' started by tomadom, Nov 20, 2018.

  1. tomadom

    tomadom

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    Jan 18, 2013
    I have a portable solar charger and a small hand cranked generator and use them to charge a portable Power Bank.
    The only problem is I want o see how full the battery is at any time. It's connections are USB 2.0.

    Would anyone know of a small gadget used specifically for this kind of thing. I've looked on the web and it seems they all start at 12 volts when I need on which will go as low as 5 volts.

    I want something like this: https://ae01.alicdn.com/kf/HTB1ngvL...m-battery-coulombmeter-voltmeter-electric.jpg with the percentage and the level bars.

    I was hoping to find something already made but if it's not too difficult I could easily make a USB version providing I could find a meter like this which matches the voltage I want to test (USB 5.0 volts I believe).

    I know there are plenty of these things: https://c.76.my/Malaysia/[email protected] but this is not what I'm looking for.

    Any suggestions?
    Thanks
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Evaluating the charge level of a rechargeable battery is notoriously difficult. You need to know the nominal capacity as well as e.g. temperature, age etc. (read here). I know of no universal meter for this purpose.
    In addition you cannot measure the battery's state on the USB port of the power bank. The powerbank has an internal battery at ~3.7 V and a switch mode step-up regulator to deliver 5 V on the USB port. You'd have to connect a metering circuit directly to the internal battery.

    I recommend you buy a power bank with integrated state-of-charge indictaor similar to e.g. this one
     
  3. BobK

    BobK

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    Jan 5, 2010
    All of the 5V power banks I have seen have 4 LEDs to show the state of charge.

    Bob
     
  4. dave9

    dave9

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    Mar 5, 2017
    I have a 18650/USB output power bank with a % indicator LCD display, but it's not very accurate.

    If your power bank design uses cells in parallel instead of series, then they will self-balance and you could just use a voltmeter module to see remaining voltage. While not a percentage, it would instead have the benefit of more granularity, and give you some positive mental reinforcement while you're cranking away at the generator, that it's doing something. :p
     
  5. tomadom

    tomadom

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    Jan 18, 2013
    Thanks for the replies. I'm not looking for a precision instrument. I want something to take travelling which can be used to see if I am actually putting any power into my power bank or not. Something with an actual Percentage and bars would be great.

    I'm really surprised something like this doesn't exist. My power bank has 4 or 5 bars on it but I would like something external to the power bank. I want to know, if camping/travelling whether my solar panel or hand cranked generator has put anything into my battery.

    The aliexpress kits look interesting.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If it is a lithium battery (or lead acid) then the cell voltage is an indicator of charge. For lead acid you also need to take the temperature into account.
     
  7. tomadom

    tomadom

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    Jan 18, 2013
    So I just need a volt meter to tell me how full the battery is?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    24,860
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    Jan 21, 2010
    If all the cells are equally charged and not under load (or being charged) then there are battery voltages that will correspond to empty, 1/4, 1/2, 3/4, and full.
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    1,691
    Nov 17, 2011
    Remember: you need to measure at the battery poles, not the output of the power bank.
     
  10. tomadom

    tomadom

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    Jan 18, 2013
    Thanks for the help everyone.. I haven't come up with a compact solution yet but am working on it.
     
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