LED trunk lighting

Discussion in 'The Projects Forum' started by Doktor Jones, Jan 31, 2014.

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  1. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
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    My fiancee's closet has been a notorious black hole, with stuff getting lost in the dark corners of it. I have a 12V battery available to power this project. Before I go buy all the parts, can anyone please confirm that this is a sensible schematic?

    I chose a pair of constant-current LED drivers to account for the varying voltage coming from the battery, using a reed switch and MOSFET to switch them, and put the whole thing on a 2A fuse for safety.

    The drivers: https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?productId=2006932
    The LEDs (three in series per driver): https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?productId=2153166
    The MOSFET is your garden variety IRF630 (with protective diode built in), and the reed switch is rated at 0.2A, which I figure should be enough to flip the MOSFET.

    I'm not sure if I can put the drivers in series since the LEDs are only 3.4V, or if the driver needs >= 9V to drive them (and would thus need to be in parallel). If anyone has any thoughts on this, or on any other parts of my circuit, please let me know. Thanks!
     
    Last edited: Jan 31, 2014
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Automotive topics are banned on this site for safety reasons.. not sure if this really classifies..

    But use Meanwell LDD drivers.. They are cheaper..
    You could use the meanwell LDD-350HW (only $6.95 ea at Jameco)
    It has wires on it already too (W is the wired version..pic on their site isn't proper)

    And I'd simply use a cheap ($5 or less) snap action lever switch vs having to mess with a mosfet/reed switch..
    And you don't put the drivers in series.. they go in parallel..
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Oh, it's lighting in the trunk of a car. No, it's a trunk in the closet. No, it's just a closet. :)
     
  4. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
    57
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    Okay... so just
    Code ( (Unknown Language)):
    1.                              ,- Driver -,
    2. +12V --- Fuse --- Switch ---<            >--- GND
    3.                              `- Driver -'
    then?

    Looking at the LDD-350H, with an 18.2W max output rating and the fact that my light strips are 1W apiece, could I connect six light strips to a single driver? Or would that only be possible with a ~20V+ supply? How do I figure out what exactly a given driver can safely drive based on its ratings and my input voltages?

    (BTW I'm looking at the LDD-350H instead of the LDD350HW because the lead time on the HW is 50 days -- yikes!)
     
    Last edited: Jan 31, 2014
  5. #12

    Expert

    Nov 30, 2010
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    This worked before you changed the question. Now I have to go do another chore.
     
  6. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
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    Okay, that looks simple enough. Looking at the datasheet though for the Mean Well drivers, it looks like the drivers should be connected to battery ground themselves, and the LEDs should be connected to the +/- outputs on the drivers, i.e. don't connect LED (-) to Battery (-). Does that sound right?

    http://www.jameco.com/Jameco/Products/ProdDS/2155882.pdf

    Apologies for changing the question, it was just sort of a segue :p
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The pdf has a small misprint.

    In reading the specs. I came to the MTBF entry.

    2000Khrs. Is that 2,000,000 hours? Impressive.

    More likely the time was 2000 hours. The warranty is only three years and that equates to 26,200 or so hours if used 24/7. If the unit had 2000Khrs between failures I would advertise it as a lifetime warranty. I think that is actually longer than the LED's are supposed to last
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    For your circuit choosing a 0.5A fuse is better, for the circuit provided from #12 that it choosing a 1A fuse is better.

    You should care about the +12V that does it really a fixed 12V or a 12V battery then it could be 13.8V or some more, and it will affecting the current of LEDs.
     
  9. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
    57
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    Well I intend to have two drivers in parallel... if they're each driving 350mA of LEDs then that's 0.7A... pop goes the fuse? That's why I'm looking at 2A. Small current spikes and whatnot won't faze it, but anything of significant concern (like a short) will pop a 2A fuse in short order. If you were referring to my original diagram with the drivers in series, 0.5A might work, but I still think it's a little shy on headroom; I'd prefer 1A for a single driver (or drivers in series) and 1.5A-2A for two drivers in parallel I think.

    The 12V does come from a battery, so it can range from ~11V to 13.8V. Isn't that the point of a constant-current driver though, so I don't have to try to compensate for this myself? If I'm using 10.2V of LEDs (3 x 3.4V in series), I don't think the battery voltage will be a problem until the battery is effectively dead anyways (which shouldn't happen in the first place).

    Looking back at the datasheet, I noticed that the input current draw for all models on the datasheet are lower than the drive capacity, so I'm thinking this might be a buck driver as opposed to buck-boost -- so I would indeed be limited to the 3 LEDs per driver. I'm okay with this, but I just want to make sure I'm understanding the capabilities and limitations of the driver before plunking down the cash for the hardware.
     
  10. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
    57
    1
    Another segue (sorry!)... if I were to use these LEDs instead... http://www.mpja.com/90-lm-1-Watt-White-Star-LED/productinfo/19585 OP/

    What sort of heatsinking would be considered adequate for them? If they were bolted to a steel panel (>3"x3") would that be sufficient, or would they need fins/airflow?

    They're substantially cheaper than the LED strips I was looking at, and possibly a little more versatile in that they don't need to be attached to a wide flat area, but I want to make sure I don't heat-fry them either.
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Omg. Such an obvious attempt to circumvent forum ToS and it hasn't been shut down. Go to electrotech instead.
     
  12. Doktor Jones

    Thread Starter Active Member

    Oct 5, 2011
    57
    1
    If you have something constructive to contribute on the discussion of the principles and applications of LED drivers on a ~12V power source I'm eager to hear your thoughts. If such talk offends you, far be it from me to prevent you from excusing yourself from such profane discourse. I'm just trying to learn more about LED lighting (a pet obsession of mine). Thanks!
     
  13. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    djsfantasi has a valid point to make.

    The owners of All About Circuits have elected not to allow discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Here is a site that may provide you with some assistance: Electro Tech Online

    Good luck.
     
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