beginner needing help with 12v LED lights.

Discussion in 'The Projects Forum' started by mattriser, Mar 2, 2014.

  1. mattriser

    Thread Starter New Member

    Mar 2, 2014
    3
    0
    Hello all,

    First off, I want to make it clear that I know NOTHING about electronics... I don't know what "watts" are, or what "AC/DC" means or "volts" or any of that stuff...so please, if you respond, dumb it down for me.

    Basically I'm an artist that is trying to light up a relatively small project.

    I just ordered some Led modules (designed and intended for channel sign letters) from ebay and I'm hoping that there is a way to light them up using a 9v or similar(small in size) battery.

    So far, all I know is the lights I ordered are 12V....and if you look at the auction picture, the lights have "DC12V" printed on them.

    I tried to get information from the seller, but I think there is a bit of a language barrier.

    When I asked him how I can light them up he stated:

    "you need

    led module +power supply +dc connector female
    ( you need 5 watt power supply we do not have)

    we 24 watt power supply"

    When I asked him if I can use a battery he stated:

    "can solder.
    LEDs, works with 12 volts."

    Can someone, in laymen's terms, tell me exactly what I need to light them up with a battery.

    Thanks,
    Matt
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,768
    4,804
    Assuming that what you have are intended to operate from a 12V DC supply and pull 5W doing it, you would need a DC-DC converter to get your 12V from a 9V battery. If each module is designed for 5W, then each module will draw about 400mA from the output of the converter and, assuming a 90% conversion efficiency, about 600mA from the battery. At that discharge rate, you can expect a typical alkaline 9V battery to last about 30 minutes. You also would not want to try to power much more than one module from a single battery even if the short lifetime were acceptable.

    There are LOTS of DC-DC converters available, depending on your needs and budget. You can find a lot of options at any hobby store that caters to radio-control enthusiasts. They are often called "battery eliminators" (because the idea is that instead of having multiple batteries of differing voltages, you have a single battery and use an eliminator to produce the other voltages).
     
  3. bertz

    Member

    Nov 11, 2013
    238
    31
  4. burger2227

    Member

    Feb 3, 2014
    190
    24
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Your suplier suggested a 5 W power supply so the supply needs to be able to supply . 416 amps, A, at 12 volts, V. W/V = I, current or A, so the AC adapter, wall wart, AC/DC Adapter suggested in post # 3 at 12 W should do well and could supply more strings,
    If V supply must be batteries, then as an example, 10 Ni-MH, AA cells in series, would operate the LED's for about 6 hours.
    When yuo receive your LED's, give us a detailed discription , especilly the connector & colors & I'm sure that somenoe here can help with connections.
     
  6. mattriser

    Thread Starter New Member

    Mar 2, 2014
    3
    0
    Thanks for the responses... I'm thinking that the lights I got are not really going to work like I had hoped... but I will buy the recommended power supply and and play around some more.

    But I really need something that is going to last a long time and run off of a battery... so perhaps you guys can help me again with some other LEDs that I bought a while back.

    The package reads:
    "5mm round white 3.0-3.4v / 24mA max / 27,000 mcd"

    and as i stated before, I have no idea what this all means, excpet for the 5mm part.

    So my question is..... what kind of battery(or batteries) would work best to power 3 of these little guys for a really long time?

    I've done some reading and it looks like I may need to solder a resister or something in somewhere.

    So, please, if anyone knows that best route...let me know.

    thanks again,
    matt
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,768
    4,804
    If I asked you how much paint I need to paint a really big picture, you'd come back and tell me you need more information before you had any hope of giving me a reasonable answer, right?

    It's the same here. I have no idea what you mean by "a really long time". An hour? A month?

    Similarly, if I asked how many colors of paint I need to paint a good picture, you've need to know a lot more about the picture I wanted to paint before you could answer it.

    Same here. The size battery that you need to keep one LED lit for six hours is very different from the size battery that you would need to keep two hundred LEDs lit for a week.

    We need a much better idea of what you have in mind. At the very least, we need to know how many LEDs you are looking at in total and how long you want this battery to last, in terms of the amount of total time it will need to keep the LEDs lit. There will be other things that will affect the answer, but these will give us a starting point.
     
  8. bertz

    Member

    Nov 11, 2013
    238
    31

    OK, first let's interpret the specifications for your LEDs.
    5mm = diameter of the package
    round = obviously the geometry of the package
    white = color of the LED
    3.0 - 3.4 volts = this is the forward voltage drop range; higher current, higher drop. We need this to calculate the resistor value.
    24 mA max = this is the maximum current the LED can handle
    27,000 mcd = brightness of the LED in millicandles; this is VERY bright

    OK, lets stick with powering these little jewels with standard AA alkaline batteries. Four of these batteries will supply a nominal 6 volts. I said nominal because the voltage will tail off as the battery discharges. You can pick up a nice battery holder at Radio Shack or from e-Bay like this:

    http://www.parts-express.com/4-aa-c...source=google&utm_medium=cpc&utm_campaign=pla

    Now lets calculate the value of the current limiting resistor for 15 mA.
    (6 - 3.2) / .015 = 186 ohms

    Watts = 2.8 volts x .015 amps = .042 watts; a 1/4 watt resistor is sufficient

    This is an oddball so lets go with the next higher value standard resistor which is 220 ohms. Then the current through each LED will be:
    (6 - 3.2) / 220 = 13 mA x 3 = 39 mA total

    From the Energizer website:
    Standard Energizer AA (alkaline): 1.5V, 2850mAh
    Energizer E2 Lithium AA (alkaline): 1.5V, 2900mAh
    That means the standard battery will deliver 2850 mA of current for 1 hour. But we are only pulling 39 mA so then:
    2850 mAh / 39 mA = 73 hours (theoretically)

    I doubt you'll get 73 hours, but you get the idea.

    Good luck!
     
    Last edited: Mar 3, 2014
    mattriser likes this.
  9. bertz

    Member

    Nov 11, 2013
    238
    31
    This is how you would connect everything up.

    Good luck!
     
  10. burger2227

    Member

    Feb 3, 2014
    190
    24
    The 5252F chip I mentioned above can supply 3, 3 volt LED's in parallel with 10 ma each using one 33 uH coil and one AA battery for over 24 hours.

    No resistors. The coil determines the current delivered

    Bright LED's normally can use 3 volts with up to 30 ma each, but don't look at them long or directly!
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    3 LED's in parallel will waste about one half of battery power. I would try 3 LED's in series with 8 Ni MH, AAA, 2650 mAh, for abuot 132 hours, or 8, AAA, for about 42 h, with 47 Ω resistor @ 20 mA. If necessary, add 2 more cells depending on LED Vf. I normally measure each LED's Vf.
    I do not think a 2 cell Ni-MH charger is verry expensive; mine was $ 1.50 at yard sale. The Ni-MH cells have a much flatter discharge V than Alk. & stay at about 1.25 V for most of discharge cycle.
     
  12. burger2227

    Member

    Feb 3, 2014
    190
    24
    Waste half of what battery power? One AA for over a day? @ 30 ma, that's just 720 mah so perhaps 2 days or more.

    Series cuts the voltage so you need 3 times as much battery. Most bright LED's need 3 volts and 10 or 20 ma. A 10 uH coil could deliver 30 ma to each one in parallel if you really need it.
     
  13. mattriser

    Thread Starter New Member

    Mar 2, 2014
    3
    0
    Thanks Bertz,

    I think you answered my questions best...I truly appreciate it.
     
Loading...