How to manage battery life in small area

Discussion in 'The Projects Forum' started by Jlwoodfloors, Apr 2, 2016.

  1. Jlwoodfloors

    Thread Starter New Member

    Apr 2, 2016
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    First I hope I'm in the right forum. I am running 2 3w leds with a 5v rf transmitter. Having problems fitting enough voltage and mah in a small area. I'm trying to fit all this in a 1inch square aluminum tube by 2inches long. Batteries are a big issue was wandering if there is anything I can do toto prolong batteries it seems the rf transmitter draws a lot of juice. Have tried li-poly batteries but die out to quick. Trying to get at least 6 hours of work out of the leds. With the 2 3.7 volt lipoly in series only getting 1hr 250 mah per battery . Also tried aaa rechargeable 1.2v with 800 mah per battery. Maximizes space leds last for about 4 to 5 hours but can only use rf in the first hour. Please help me it's driving me crazy.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Start by measuring the current drawn by the transmitter and leds, this will give you a start as to how long these batteries will last,
    Only then can you select your battery, size and capacity.


    Try looking at 2/3 aa nimhi 1800maH, or 18650 lion.
     
  3. John P

    AAC Fanatic!

    Oct 14, 2008
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    For the LEDs, it sounds as if you need 36 watt-hrs from a battery that occupies 2 cubic inches of volume, so 18 wh/in^3, and there are 61 cubic inches in a liter, so it would be 1098 wh/liter.

    Supposedly the LiPo battery in an iPhone 6s has an energy density of 703 Wh/l, so you may be too ambitious there, but not by a huge amount. Are you running your LEDs with an inductor-based constant current regulator, or just a resistor? If it's just the resistor, you've wasting a lot of power.
     
  4. Alec_t

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    Sep 17, 2013
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    If you can pulse the Tx and/or LEDs with a low duty-cycle you can reduce the average power consumption dramatically.
    Just curious; is this a recovery beacon you're building?
     
  5. John P

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    Oct 14, 2008
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    The LED brightness can be traded off for longer battery life, to any extent you want, but I assumed 2 3W LEDs meant 6W power consumption. Actually if it is a beacon being used for maximum visibility, a flashing light would probably work better than a steady light, and would use less power.
     
  6. Jlwoodfloors

    Thread Starter New Member

    Apr 2, 2016
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    No just a resistor can you tell me more about this current regulators
     
  7. Jlwoodfloors

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    Apr 2, 2016
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    Not a beacon how would I pulse the TX and or LEDs with a low duty cycle please tell me more
     
  8. Jlwoodfloors

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    Apr 2, 2016
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    How do I measure draw of current I have a voltage meter.
     
  9. Dodgydave

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    Jun 22, 2012
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    You need an Ammeter, if you only have a voltmeter you need a 1ohm resistor in series with the battery.
     
  10. bertus

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    Apr 5, 2008
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    Hello,

    Do you have a multimeter or a pure voltmeter?
    A multimeter will have a current setting.

    Bertus
     
  11. Jlwoodfloors

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    Apr 2, 2016
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    Multi meter
     
  12. Dodgydave

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    So set it to mA amps, and measure the current from the batteries with the transmitter working.
     
  13. Jlwoodfloors

    Thread Starter New Member

    Apr 2, 2016
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    Thanks I will try that
     
  14. bertus

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    Hello,

    Do you also have details on the leds to be used?
    The 3 Watt leds I know of use a current of 700 mA.

    Bertus
     
  15. Jlwoodfloors

    Thread Starter New Member

    Apr 2, 2016
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    I will have to do some more research on that all it says on packagING is 3w
     
  16. atferrari

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    The 200 mA setting of the DMM could be not enough. Betjer to do a first test with the higher setting which is quite often, unfused. 10A maybe?
     
  17. Alec_t

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    The pulse circuit could be based on the ubiquitous '555 IC, but the details would depend on how much current the LEDs and Tx need and the duration of acceptable 'on' and 'off' periods.
     
  18. John P

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