LED double staffs

Discussion in 'The Projects Forum' started by Ross Thebridge, Oct 29, 2015.

  1. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    Hi,

    I am working on a LED double staff project and currently working through a power solution.

    I am using 6 x AA Eneloop batteries for power. I will be running 2 banks in parallel. Each bank will be 3 x 1.2V 2500mAh providing a total of 3.6V at 5000mAh.

    I am now looking for a step-up converter to go from 3.6V to 5V (the controller and lights are 5V). It would also be good if the converter was able to cut power when the voltage dips below around 3.5 volts (not essential though).

    Any ideas?

    StaffWiring_3.jpg
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    There are all kinds of regulators to do that, but why don't you just use 4 series batteries? Step up regulator efficiency for 3.6 to 5V will probably be 70-80%. If you add 2 more batteries, you can eliminate the complexity and power consumption of a step up regulator.
     
  3. #12

    Expert

    Nov 30, 2010
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    Intentional over-complication? Why not use 4 batteries in series to get 5 volts?

    Edit: Darn, got here second this time.
     
  4. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    Thanks Dennis. It's a weight thing. The staffs are for twirling (1 for each hand) and 8 AA's per staff is quite heavy, so trying to reduce weight where possible. I guess the bonus of 8 is I may end up with massive arms!

    I've tried 8 and would like to try scaling back to 6.
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
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    What about switching to AAA? Looks like they're 1800mAh. You'll probably get similar runtime because you won't be losing 20-30% of your battery capacitor in the step up regulator.
     
  6. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    The AAA Eneloop Pro's are 950mAH. From reading around, anyone claiming above that is basically to be read as BS. So a big drop from the 2550mAh of the AA's.

    The lights at full brightness draw 6,240mA. They won't generally be at full brightness so will prob only run at around 1/3 of that (2,080mAh). I need the AAA's as the AAA's just won't last very long at all.
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    There are step up regulators to do what you want, but efficiency is in the 70-80% range, so you're going to lose a quarter of your battery capacity in the regulator.
     
  8. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    So does that mean the 2500mAh would reduce to around 1875mAh?

    If that's the case, that may work considering there will be 2 bays, so that gives me 3750mAh in total. Any chance you can point in the direction of something that would do that?
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    There was a post within the last month or so where someone was trying to steup up 3.3 or 3.6V to 5. Google step up regulators.
     
  10. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    Haha ... I already did that! That's why I came on here.
     
  11. dl324

    Distinguished Member

    Mar 30, 2015
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  12. DickCappels

    Moderator

    Aug 21, 2008
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    An aside: Are those prefabricated strings of LEDs that are matched for voltage? If running parallel they should be matched and if possible kept at the same temperature, such as being on the same heatsink.
     
  13. Ross Thebridge

    Thread Starter New Member

    Oct 29, 2015
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    Getting a bit out of my depth now. They are from 1 strip which has been cut into 2 strips. They are both driven by the 1 controller.
     
  14. DickCappels

    Moderator

    Aug 21, 2008
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    Ok...if they were sold as a parallel array then a respectable vendor would have made sure that they are all matched for voltage. I withdraw my concern.
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Big assumption that each LED Vf 3 V in series with 33 ohm X 108 strings would draw about 12 A max or maybe 4 A average. Max loss in resistors around 12 W & with boost , batteries expected to supply about 5 A-- they will not like that.
    If using boost, why not go to 12V & use 12V strings --would save 2 R's for every 3 LED' s
    If LED's flash at 25% duty cycle, 60mA peak, current draw at 12 V =540 mA for 36 strings, 1.8 A at 3.6 V + loss =2.25A
     
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