LED "light box" - 3 circuits with 1 switch?

Discussion in 'The Projects Forum' started by cjartguy, Dec 3, 2013.

  1. cjartguy

    Thread Starter New Member

    Dec 3, 2013
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    Project: a "light box" (for a backlit logo on a rolling cart) using multiple battery-powered, stick-under-the-cabinet, push-on/push-off lights. Each under cabinet light module consists of 5 LEDs powered by 3 AAA batteries.

    Original Plan: dismantle two units, and wire them both to a double pole single throw switch (leaving the existing push-on switches in each unit in the "on" position, as they will be inaccessible inside the light box). The DPST switch will be located on the side of the cart to turn both light modules on simultaneously.

    Problem: Still not enough light!

    Questions: What's the best/easiest way to add a third module? Can it share leads to the switch with one of the other modules? Or should I dismantle the third module further, removing the batteries and wiring the LED strip into the same circuit as the second module?

    Thanks in advance!
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I'd consider adding another switch. Not elegant, but you already know how to do it and it will definitely work for you.

    I would avoid any solution that parallels power supplies (the AAA battery packs) unless you can start them all with fresh batteries that are as similar as possible. Same manufacturer, freshness, etc. In that scenario you could use a single larger battery pack and switch the power to all lights at the same time.
     
  3. cjartguy

    Thread Starter New Member

    Dec 3, 2013
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    Yep, I was afraid that. Clunky wins out this time. I realized I was over my head with the multiple power supplies. Thank you for your advice!
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are triple pole switches available if you really want one switch for all three modules, but they are a little pricey. Here's one example; it happens to be 3PDT, but would work.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    It just comes down to what you want, quick and clunky or built to last. If you were doing the latter, you might consider making a single power supply. A 5V power supply (such as just about every USB smartphone charger these days) would probably work. Maybe a 12V battery plus a 12V-to-5V car charger adapter if you need mobile battery power. Or 3 D batteries to replace all the separate AAA packs.

    Point is, there are a lot of options. Only you can decide which to pursue.
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    That would be a good choice if the cart has no AC. The savings in battery costs would add up quickly.
     
  7. cjartguy

    Thread Starter New Member

    Dec 3, 2013
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    If I were to just wire a 3 "D" battery pack and the three LED strips in from the 3 modules (in a "chain" sequence), would there be any issues with the resistors attached to each 5-LED strip?
     
  8. wayneh

    Expert

    Sep 9, 2010
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    You would place them in parallel, not in series. In parallel, one chain won't know or care about the others except for the added drain on the batteries, which will slightly drop the voltage.
     
  9. cjartguy

    Thread Starter New Member

    Dec 3, 2013
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    THANKS! I think this will be a great solution. I appreciate everyone's advice!
     
  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It may be that you can't find a holder for three D cells, and have to buy three holders, each for one D cell. In that case, you would wire the three holders in series. That's what I did for a portable power source for PIC programming.
     
    Last edited: Dec 3, 2013
  11. cjartguy

    Thread Starter New Member

    Dec 3, 2013
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    I found a holder for 4 D cells. I'm just going to solder a wire to bridge the last slot. Should do the trick, right? Thanks.
     
  12. tracecom

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    That will work.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Agreed. For what it's worth, you could also use 4 Ni-cad rechargeable batteries since these have a lower nominal cell voltage (1.2 vs 1.5V). Four in series would not likely be a problem for your LEDs; 4.8V for 4 cells vs 4.5V for 3 alkaline D cells.
     
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