12v leds

Discussion in 'The Projects Forum' started by Quazar, Aug 12, 2013.

  1. Quazar

    Thread Starter New Member

    Aug 12, 2013
    8
    0
    Hi: I'm not a major electronics person so far but have acquired some of these leds and would like to know how to wire them in a series circuit preferably a 12v dc circuit (T10 White 168 194 501 W5W 5 SMD LED Car Side Wedge Light Lamp Bulb DC 12V) . I would like to use a 12v solar panel charging a deep cycle battery that would power them at night. If possible with a light sensor to turn them on/off at night/day. I am not stupid just ignorant of these matters but I can follow directions well. I would appreciate your help.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,086
    3,024
    Your essentially describing a beefed up solar landscape light. The devil is in the details. You need to start with how much light power you'll need, for how long at night. I can't tell from your post what the details of the LEDs are, in terms of voltage and current, and power. Do you hope they will remain lit all night? In late December after a snowy day?

    Once you know how much light power you need, you'll need a panel rated to about twice that, to allow for all the combined losses in battery charging and so on.
     
  3. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    Darn! Wayneh beat me to it again!:D

    But seriously, I let this one go to wayneh because I feel discouraged when somebody wants to design from scratch something that you can buy retail for $20 or $30. There is so much work in it, and it will almost always cost more for parts than buying the retail version.

    You want this one? You go girl! :D
     
  4. Quazar

    Thread Starter New Member

    Aug 12, 2013
    8
    0
    I hope the leds will have more information when they actually arrive. They are from the automotive industry There appears to be 5 leds mounted in clusters in each socket. Being as they are designed for a 12 volt automobile system it may be necessary to wire each one in parallel. Hoping that they arrive with some kind of specifications. They are going into a yard art project and each socket will be in a different location with about 3' of wire between each. In the event that specs are not handy, is there a way I can determine them with a mult-meter? Thank you for responding.
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Depending on how much these cost you, you might be better off getting edge lights (small landscape lights that do exactly what you are describing) from a dollar store (and they literally cost $1 each) and tearing them apart to get the stuff you need.

    Since you are probably planning to tear your car lights apart in order to integrate them into your art project, you can get some of the information you need by measurement. Many multimeters today have a diode check feature that will tell you the forward voltage across the diode when it is conducting a small current. Some of these work well for LEDs as well as normal diodes.

    But let's assume that yours doesn't.

    Take one of your LEDs and wire it through a resistor to battery (your planned 12V supply or even just a 9V battery). Pick the resistor so that about 5mA should flow through the LED. A close enough approximation can be done by just dividing the battery voltage by the desired current. So for a 12V source you would pick 12V/5mA=2.4kΩ. Anything close to this will be fine. If the thing doesn't light, reverse the LED (or the battery) and try again. For whichever way it lights, ask yourself if that is bright enough. Also, with your meter, measure the voltage across the LED and make note of it. If you want it brighter, choose a smaller resistor. A typical off-the-shelf LED wants a current somewhere between 2mA and 20mA, but an automotive LED might be designed to consume a lot more current in order to be bright enough to be seen at a distance. Just keep using smaller and smaller resistors until you get an intensity that satisfies you, keeping in mind that you may be choosing an intensity brighter than what it is designed for.

    Once you have the intensity you want, make note of the voltage across the resistor and use Ohm's Law to determine the current that is flowing.

    Have you figured out how you are going to access the individual LEDs? The part number strongly implies that they are surface mount devices (SMD). Or are you planning to use them as units and not tear into them (which would be my recommendation)?

    If that's the case, you can do something pretty similar, but they may well be designed just to power directly from 12V and be done with it.
     
  6. Quazar

    Thread Starter New Member

    Aug 12, 2013
    8
    0
    I am not planning to dismantle the units but use them as is. I suspect they are designed to rum on 12v. I may try one as is to test the theory when they get here (there are 80 coming). If so I will measure the current as you suggest to the size solar panel and battery I would require to run them for about 10 hours. If so is there anything that should be put in line to protect the leds? You are very helpful.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,979
    3,703
    Lets say that each of these lamps will draw about 0.1 to 0.2 amps. Using 80 at the same time will need 8 to 16 amps of power at 12 volts. That is a pretty heafty battery. Make sure yu use heafty wire too - especially from the battery to the branch points. 12 gauge would be about right for 16 amp (0.2 amps per Lamp). If the draw is only0.1 amp, then 16 gauge will work for you.
     
  8. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    Pre-fabricated lamps rated for 12 volts would almost certainly have the current limiting built in. We will need the current measurement.
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,086
    3,024
    Way to go girl! :D
     
    #12 likes this.
  10. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    Quazar changed the subject to something you can't buy in a Home Depot, so I stand embarrassed.:p
     
  11. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    I tried to do some checking and couldn't identify the exact unit the OP is talking about, but the ones I did find never mentioned a current or power rating. Wierd.

    I did find several, though, that appear to be units that are connected to the vehicle's CAN bus. This makes a lot of sense (from certain perspectives). Just run power and a CAN bus to everything in the car, even the side marker lights, and have the computer tell them what to do in response to what the switches tell the computer to do, given that they are simply units on the dash or steering column that have nothing but power and the CAN bus running past them.

    The engineer in me loves the simplicity and the elegance of putting everything into one basket, but the engineer in me hates the complexity and the risk of putting everything into one basket.
     
    Last edited: Aug 14, 2013
  12. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    and the repairman in me hates the idea of replacing a multi-hundred dollar, proprietary module to fix a light bulb.
     
  13. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Oh, how I hear you there. A bulb goes out in the dash and you have to replace the entire instrument cluster? Come on!!!
     
  14. Metalmann

    Active Member

    Dec 8, 2012
    700
    223
    That's another reason I hate these new, expensive, plastic; vehicles.

    The old cars.....I could do a tune-up on. Not today.....;)
     
  15. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    I agree. I've done brake jobs in a mountain meadow when a brake lining started separating and have replaced more than one starter or alternator on the side of the road plus numerous other repairs. Those days are pretty much over. No longer can you clean the points with a pocket knife and then gap them with a matchbook cover and limp it on home.

    Now, at the same time I have to admit that the newer cars get much better mileage, have far better emissions, you can put two and three times the total miles on them before they are junk, you aren't having to do some kind of maintenance on them nearly every weekend, and they really don't break down nearly as often. Not to mention all the bells and whistles, many of which are very nice (though since I've never owned a new car and right now my car is a '99 and my wife's is an '01, I don't have very many of them).

    So, like all things, it's a mixed bag -- not all good and not all bad.
     
    Last edited: Aug 14, 2013
  16. Metalmann

    Active Member

    Dec 8, 2012
    700
    223
    That reminds me, that I have only bought two brand new vehicles in my entire lifetime.
    Neither one really needed any maintenance, (Basically oil and gas), until I traded them in.

    These days, I am back to used vehicles, like my new/used Jeep.:D
     
  17. Quazar

    Thread Starter New Member

    Aug 12, 2013
    8
    0
    Hello: Here is the latest. The leds arrived with no specs or paperwork. As of yet I have not figured out how to measure the current through it. I thought I would try some physical tests using one unit as a sacrificial lamb. First I hooked it up directly to a 9v battery with no resistor. It lit up with no evident problem. Thought I'd push the gambit and tried the lowest setting on my car charger (2 amps). Still lit up without incident, next setting was 10 amps - still lit up but a little brighter, went for broke and hit the 50 amp switch for about 20 seconds, lit up much brighter and got somewhat warmer so I reverted to 10 amps and it has been on for about 12 hours now. I still have no resistor in the circuit. After some web searching I found what appears to be the same lights(replaces the same automotive lights and look the same) with specs of "working current=40-50ma, power wattage=0.5w" If I use apply Ohm's Law (12v/.05A) I get R=240Ohms. Why did this light not blow out when 50 Amps was applied? Also it appears the current required will be way to much to make a solar panel practical so I will probably need to figure out how to how to hook 60 to 80 of these to a 120v/15amp household outlet. I apologize for my ignorance. Tom
     
  18. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    You different charger settings are producing somewhat higher voltage as you go to higher current settings, but like all voltage supplies, the actual current delivered is dictated by the device being powered.

    If you connect a 100 ohm resistor to a 12V supply, it will draw 120mA, right? Did I have to tell you that it was a 12V, 120mA supply? No. It would draw 120mA if it was a 1000A supply. Now, if it was a 10mA supply, then you know that it will draw, at most, 10mA because the supply is not capable of putting out any more than that.

    Having said all that, be aware that Ohm's Law doesn't apply to LEDs or another other nonlinear device. You can get in trouble trying to use it as if it does.

    Do you have any resistors handy. If so, put your charger on the 10A setting and put a resistor in series with your LED lamp that is in the 20 ohm to 50 ohm range. Use your multimeter to measure the voltage across this resistor when the LED is on. Then use Ohm's Law on THAT voltage and the value of THAT resistor to calculate the current.

    At 50mA each, your total current needs for 80 such lamps in parallel would be about 4A, which is pretty tractable to deal with.
     
  19. Quazar

    Thread Starter New Member

    Aug 12, 2013
    8
    0
    Put a 33 ohm R in the circuit as suggested and came up with about 40mA. That puts the current even lower at about 3.3A.
     
  20. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Good. Now, expect the current to vary somewhat from unit to unit and also with temperature. So give yourself some room and use a power budget of at least 5A.
     
Loading...