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Thread: USB powe bank and dual 5730 LED USB stick runtime?

  1. #1
    Flashaholic* fire-stick's Avatar
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    Default USB powe bank and dual 5730 LED USB stick runtime?

    I have an "11,000 mAh" USB power bank and a dual LED 5730 USB stick.
    The LED stick has 2 resistors: R1=06E and R2=390.
    I was wanting to know how long this would run. I am hoping to use it for emergency type lighting like a candle if the lights go out.
    I looked up online that the LED's are 60 mAh but didn't know if they would be getting the full power due to the resistors.
    I did some rough math and didn't know if I was even remotely close. I know the power bank is probably not going to deliver the full "11,000 mAh" and the LED's may be 60mAh or possible less due to resistors. Rough math displays that 11,000mAh / 120mAh is 3.8 days but I may be off by a large factor due to above mentioned reasons. Even if the resistors reduce the power by 25% I could be off by a large amount.
    I looked up the resistors and am stumped because it said R1 was 1.13Mohms and R2 is 39ohms... I have no clue what that means, I mean I know its mega ohms but I don't know what to do from here.

    http://kiloohm.info/eia96-resistor/06E
    http://kiloohm.info/smd3-resistor/390

    Any help would be appreciated. If anything this should be very educational!!! Thanks!!

  2. #2
    Flashaholic* DIWdiver's Avatar
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    Default Re: USB powe bank and dual 5730 LED USB stick runtime?

    Turn the 06E upside down, and it becomes 390. This is a very reasonable resistor value for that purpose.

    if the LEDs are white, and the powerbank puts out 5V, you'd have (5V-3V)/39 ohms = 0.051A, or 51 mA. Sounds about right.

    Times 2 for two LEDs is 102 mA, that would run theoretically 108 hours.
    Last edited by DIWdiver; 12-02-2020 at 05:51 PM.

  3. #3
    Flashaholic* fire-stick's Avatar
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    Default Re: USB powe bank and dual 5730 LED USB stick runtime?

    Quote Originally Posted by DIWdiver View Post
    Turn the 06E upside down, and it becomes 390. This is a very reasonable resistor value for that purpose.

    if the LEDs are white, and the powerbank puts out 5V, you'd have (5V-3V)/39 ohms = 0.051A, or 51 mA. Sounds about right.

    Times 2 for two LEDs is 102 mA, that would run theoretically 108 hours.
    Well I took one for the team and carried that thing around all weekend! It ran 2 full days and 10 hours so 58 hours. I guess that 11000 mah block was not all it was cut up to be but figured that much! But heck though, you wouldn't need a light during the day so that's be almost 6 days at 10 hrs a day.

    PS I got a good laugh out of reading that resistor value upside down. Glad I'm not working on a space ship or someone would be in big trouble!!!

  4. #4
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: USB powe bank and dual 5730 LED USB stick runtime?

    You have to remember that power banks are typically powered by lithium ion batteries that are 3.7v nominal and are boosted to 5VDC and the process of boosting reduces the total mah of the power bank delivered to the LEDs. Some power banks are more efficient than others without knowing how efficient the power bank is you can only guess how long it will run. When people ask me how many times they can charge their phones from power banks I tend to divide the mah by 2 because there is 2 voltage conversions going on, one is boosted from the power bank then bucked (hopefully) in the phone charging circuitry. Better power banks are more efficient than others and the rated mah can also be exaggerated too. As the batteries deplete the circuitry will try and keep the 5V level on the power bank and more current will be drawn from the batteries to keep the voltage boosted leading to reduced runtimes.
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