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What am I missing?

  • Ignatus Saturday, January 14, 2017 12:02 AM Reply

    I bought two of these modules and they are super simple to program.


    Unfortunately, they can not display the battery capacity while there is a load connected to the battery.


    The display's percentage readings jump unpredictably from 100% to 30% up and down without any proper level-indication being readable. Once the load is disconnected they indicate relatively accurate the level of the left-over battery capacity.


    I was hoping these modules could be used while the battery-pack is in use, just like any other powerbank that has the famous "4 Leds" simplified remaining powerlevel indicators (eg.:1LED for 25%, 2LEDS glowing for 50%, 3 for 75% and 4 for fully charged).


    What am I missing? Is there anything I can do to make these modules accurately display a battery's capacity while it is being discharged?


    Thanks,

    Ignatus




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    post edited by Ignatus on 1/15/2017 at 3:01 AM
  • sheepish Top 10 Forum Poster Saturday, January 14, 2017 4:27 PM Reply

    I just got one of these but haven't used it yet.


    Any load on a battery causes a voltage drop on the battery's output voltage because of the internal resistance of the battery and Ohm's Law. The greater the load, the greater the voltage drop produced.


    The meter calculates the remaining capacity based on the voltage it sees, so the greater the load the further away the voltage will be from the voltage that the meter thinks corresponds to the actual remaining capacity percentage.


    The 4 LED meters aren't actually any better. I can get the same basic effect as I've described above with my 3 mode headlamp and its 3 LED meter in the power button. Depending on the state of charge and the internal resistance of the battery being used, on low the button will light up green, on medium high the button will light up cyan, and on high the button will light up red, but the actual state of charge of the battery hasn't changed significantly.


    In other words, no.

    Remembering 30 years.
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  • Ignatus Saturday, January 14, 2017 5:30 PM Reply

    @sheepish


    Thank you for taking the time to explain to me the laws of electronics.


    It is very much appreciated!


    Kind regards,

    Ignatus



    P.S. Alright, then my only chance to implement this meter is to measure the battery capacity without a load connected, with the help of a little switch.



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  • matrix-neo Moderator Saturday, January 14, 2017 6:10 PM Reply

    indeed internal resistance is a better indicator of the overall battery health(and ability to discharge high current but not capacity), when new the cell will have a very low IR but as it goes through more cycles and ages(remember lithium cells age even when unused in storage) the IR goes up, if you really want to know the true capacity do a discharge graph, or use the accumulated charge figure in a recent charger

    Resistance is futile-give in to DX gadget craving!
    also a voluntary mod-be nice please!
    Have an enquiry? https://cs.dx.com/ticket/index


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  • sheepish Top 10 Forum Poster Saturday, January 14, 2017 6:28 PM Reply

    ... with the help of a little
    switch.


    If you're switching more than an amp, how about using a momentary pushbutton that operates a relay, turning off the circuit?

    Remembering 30 years.
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  • Ignatus Saturday, January 14, 2017 7:15 PM Reply

    @matrix neo


    Thanks for sharing your knowledge.


    Well, it's a portable 4s3p portable battery back that I am assempbling (hopefully completing it today), using LGABF1L1865 possibly doubling it to 4s6p.


    I'd like to avoid building into the box a proper Lipo charger with display and advanced charging and discharging profiles, which would most probably weigh as much or even more than the whole battery-pack by itself and add another $50 to the build. - A true capacity reading is not needed.


    @sheepish


    "If you're switching more than an amp, how about using a momentary pushbutton that operates a relay, turning off the circuit?"



    Oh wow. -That is a SUPER NICE suggestion!

    My initial thought was that I just use a momentary push button to read the battery level when the pack is not in use. I already have some momentary push buttons laying around.


    Yes, the to-be disconnected load is around 3A/ over 1A.


    I'm trying to wrap my mind around as to what type of relay would be needed.


    Could you please advise me of a relay or module that would be suitable for my application?


    I do have here a relay that is not in use, but it is far too big even if I disconnect the aluminum cooler and ... I also just realize it is for a very differnt type of application:


    AC voltage... SSR-25DA solid state relay which I may use some day in conjunction with an un-used digital timer that is catching dust here.


    - Damn, this forum always reminds me of all the electronic components that I bought, catching dust for DIY projects that I never even started :P


    However, I intend to solder this battery pack together ASAP, so your advice will really be implemented!




    Kind regards,

    Ignatus


    Edit: added the name of the cells in use...  LGABF1L1865

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    post edited by Ignatus on 1/14/2017 at 7:28 PM
  • sheepish Top 10 Forum Poster Saturday, January 14, 2017 8:23 PM Reply

    You want a 5 pin relay, which has a "normally closed" pin as well as the usual "normally open" pin (which closes when the relay operates). By connecting the circuit to the normally closed pin, when the relay operates the normally closed contact opens and the circuit turn off.


    The relay from sku.192902 has the right contacts but it's a 24 V relay, so you might not have enough voltage from a 4S li-ion battery to operate it reliably. It might work OK, just a little slower, or it might only work when the battery is at least half full (for example).


    Maybe sku.289783 would be your best option, using a resistor to drop the excess voltage.


    @desolder any thoughts? Maybe just using a low contact resistance switch would be easiest.

    Remembering 30 years.
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  • Ignatus Saturday, January 14, 2017 10:15 PM Reply

    @sheepish


    Thank you for your feedback! SKU: 192902 is also what I looked at, after you came up with this brilliant idea ... and thought that I could open it up and manually stretch the spring a little, then it should possibly work with the lower voltage.


    Edit: I did a little reading on relays and understand now that the spring trick is only possible with relays that have a spring.


    Anyhow, sku.289783 + resistor (or any similar automotive version sourced locally without long delivery time) seems like a more solid choice, and is something I wouldn't have thought about.


    Edit: Do I understand it right that I should be looking for a 12V SPDT Relay?


    Using a low contact resistance switch? Maybe grandmaster Desolder will join this conversation and share his invalueable 2 cents.


    Greetings,

    Ignatus

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    post edited by Ignatus on 1/15/2017 at 3:36 AM
  • sheepish Top 10 Forum Poster Sunday, January 15, 2017 5:40 AM Reply

    Edit: Do I understand it right that I should be looking for a 12V SPDT Relay?


    Yes, since there are two positions the relay can be switched to. With automotive relays the switched pins are normally labelled 87 and 87a, while a SPST relay just has the 87 pin (and three others).

    Remembering 30 years.
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  • Ignatus Sunday, January 15, 2017 2:48 PM Reply

    Thank you so much for confirming, Sheepish! Also, thanks for letting me know the Pin laypout of a 5pin NO/NC automotive relay!!! I'll get mine from the rainforest place.


    Unfortunately, the project takes longer than expected. I moved away from an initial 3s3p 11.1V pack design with a booster module, to a 4s3p pack design with a buck/booster.


    I was planning to integrate everything into a single box, but only realized today that an additional buck module that I used in my intial design, for charging the 11.1V pack is obviously not working with the higher voltage 4s3p pack (when connected to a high quality 12V 5A power supply that I alreday own).


    So, now I'm on the lookout for a decent booster with current limiter for charging the 4s3p pack and since I don't yet know the dimensions of the new booster module, I won't be able to build the case/box and can't complete the project immidiately.


    I'll post some pictures of the completed project when it is done.



    There is a wealth of information that you, Desolder and others have provided over the years on DX. Thank YOU!!!


    - I wish they had a section here on DX where people showcase their projects, sku/s used and some pics of the end products.


    I think it could increase DX sales slightly, if people want to copy projects and use a BOM provided by the original project creator.


    Anyhow, on a second thought I should most probably look around for a decent DIY / hobby electronics portal.



    Success and regards,

    Ignatus



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    post edited by Ignatus on 1/15/2017 at 3:13 PM
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