LEDs in truck

Discussion in 'The Projects Forum' started by self_sponsored, Oct 10, 2007.

  1. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    I ended up getting the 62ohm resistors. I forgot that I also have some other resistors coming with the LEDs I ordered. I forgot the exact values, but I think they were 120, 270, 470ohm. I'll end up getting me a grab bag later on.
    I was thinking about doing the electrical tape deal, but I think I'll look for the silicon tape. Putting a zip tie over the silicon tape or even electrical tape would be good. I was even thinking if I could slip a crimp over electrical tape and crimp over the tape to hold it good.
    I read about the helping hands contraption, and I seen that for $18. Was gonna buy one, but I been getting so much stuff recently I forgot to pick that up.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    $18? Wow, that's expensive.
    Check Harbor Freights' website.

    You probably ordered the resistors for 12v.
    The LED specs are 20mA @ 3.4v, so...
    to calculate the resistance value, you subtract the LED's voltage drop from the supply voltage:
    13.8 - 3.4 = 10.4 (approximate, of course.)
    Now we need to find what resistance value to use that will allow 20mA current to flow when the voltage across the resistor is 10.4v
    Ohm's Law: I = E/R (Current = Voltage / Resistance)
    20mA = 10.4/R
    Swap things around
    R = 10.4/20mA
    R = 10.4/0.02
    520

    Now if you run the numbers through using 12.7 then R = 465; 470 is close enough.
    But they weren't figuring in on what happens when the alternator charges the battery! :eek: Using the 470 Ohm resistors at 13.8v would put 22.1mA through your LED's, about 10.6% more than their rated current. That would make them brighter, but they wouldn't last nearly as long as they should.

    Crimping over electrical tape - fahgetaboudit! Zip-ties rule. ;)

    Electrical tape is "old school". I don't think electricans can even use it anymore. They use "wire nuts" - screw on things. Those work great in houses; lousy in vehicles.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
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  4. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    Yea, I thought about using those wire nuts. I used them for some of my quick setero wiring in my room when I was in college. But I didn't think they'd hold up too well in an automobile.
    So I am planning on mounting strings of 3 LEDs around my truck; strings under the steering wheel, center console, dash area, passenger's feet area. I will probably just drill a small puka in the plastice trim, and poke the LED through. And then tape the back of the LED into place if it doesn't stay put. This would leave me with a problem if I decided to remove the plastic pieces (dash, center console) again later on. Everything would be wired and taped in. So I was thinking about adding a quick disconnect right before and right after the LEDs. These guys any good? http://www.radioshack.com/product/index.jsp?productId=2104016&cp=&parentPage=search
    or these guys... http://www.radioshack.com/product/index.jsp?productId=2104017&cp=&parentPage=search
    Hopefully these would hold up well to vibration. Either that or I would have to watch out for my wires and LEDs everytime I took apart my truck.
    I gotta read up on ground, cause I'm not sure about grounding vs. just using the negative terminal.
     
  5. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    Thingmaker, thanks for the links. Checked them out, and seen one helping hand for $3. They said they had USPS, but when I got to the shipping page it didn't have an option, so shipping was $21!!
    From the other site There was a good one for $8, but with shipping it came out $15. I would rather shell out $3 more and not have to wait, and especially WORRY about the shipping and whatnot. That's the downside of living on an island. That and almost $4/gallon gas:mad:
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
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    Holy Frijoles! Do they plan to ship via another planet?!:eek:

    Note: I've also seen the "helping hands" at Gem & Mineral shows, and at Gun shows.
     
  7. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    Haha, yea when it used UPS Ground to ship to HI it's a pretty ridicilous price.
    Yet another question about power. I was thinking about running all of this off of a cigarette lighter that always stays hot/on. I wanted to be able to use my lights without having to have the keys in or truck on. I will need to make sure that my lights are off when I leave my truck as to not come back to a dead battery. But just having these lights on for like 10 minutes max, with no alternator charging the battery, this will not kill my battery will it? (Based on 10 strings of 3 LEDs = 30 LEDs). I might want to see something at night but not want to turn my truck on.
    I play my stereo with the engine off (no alternator), and playing music for 10 minutes does no damage, so I wouldn't think these lights would either. For short periods of time. Like like overnight or anything.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    It's not just the possibility of coming unscrewed due to vibrations; it's the exposure of the conductors to the elements. I suppose you COULD use RTV silicone to seal them up, but that would be kind of messy. Besides, most RTV emits acetic acid when curing, which is corrosive :eek: except for a very few of them - there's a mil-spec red RTV that doesn't.
    Ahhh, sounds like it could be VERY distracting - I hope you don't plan on running those lights when you're driving?
    Also, "super-bright" LED's can damage your vision if you look straight at them for more than a few seconds, particularly if they have a narrow field of view; that focuses more of the light in one direction. Consider mounting the LED's so that the viewable light is indirect; ie:reflected from surfaces, not directly from the LED. Somehow, I thought that you wre planning on mounting these underneath your vehicle.
    Those would work just fine. I suggest that when you install them, you use the male for the positive supply, and the female for connecting the string. For the grounding end of the string, use crimp-on terminals that will fit a small sheet-metal screw. No, use the first style; they're fully insulated.
    OK, I'll try to explain it for you.

    "ground" is more or less shorthand for "earth ground, chassis ground, zero volt potential." Our planet's electrical potential is considered to be zero volts, but everything's relative ;) Your vehicle's battery has a 12.7v potential across the terminals when it's charged. In order to make connections to battery power less complicated, it was decided many years ago to connect one terminal of the battery to the chassis; thus only one wire was needed to power accessories mounted anywhere on the chassis - simply run the +12.7 wire to it, and attach the other side to chassis ground. The chassis provides the "return path" to the battery's negative terminal. This saves a LOT of wiring and weight.

    In every electrical circuit, there must be a source path and a return path for current to follow, otherwise the circuit isn't complete, and current can't flow.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    So, your battery - what is it's "amp hour" and the "reserve minutes" rating?

    Each string of 3 LED's will "draw" 20mA (we've beaten this one about to death here ;) )
    10 strings X 20mA = 200mA, or 0.2A. Get your batterys' specifications from your operators' manual, the battery itself, or the batterys' manufacturer website, and figure it out using a power draw of 0.2A, the rating, and the explanation below:

    Amp Hours

    The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.

    Reserve Minutes

    Reserve minutes is the number of minutes a battery will carry a 25 amp load before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.)
     
  10. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    For the LEDs, I will have them shining onto the ground, or at my leg area. They won't be aiming at my face. The ones in the dash area will also be aiming down toward my shifter. And I will not be driving with these guys on. I'm using it as a nice way to add some ambience, and even use them as extra lighting to see (depending on how bright they turn out to be).
    When I am grounding the negative side of the LED strings, I can either run it back to the negative cigarette wire, or I can just ground it to the body of the truck? So the body of the truck is connected to the negative battery terminal. And The negative battery terminal is connected to my negative cigarette wire. So both will produce the same result correct? I have this notion in my head that the negative wire from the LEDs NEEDS to go back to the negative cigarette wire. But I guess it's them same thing.
    I don't have my truck owners manual, I suckin lost it after owning my truck for like 2 months. So I'll check with some other owners or the battery's website for the Amp Hours and Reserve Minutes.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Yes indeedy, you'll find that practically everything in your vehicle that's bare metal will be connected to your battery's negative terminal. Your dash is most likely some kind of plastic; there is probably a separate ground wire hooked to the "bowl" of the cig lighter; the two "spring clips" and the rivet in the middle when you look inside it are all "hot", or connected (via your fuse block) to +12v. This may or may not be controlled by your ignition switch; some are, and some are not. You will probably discover that a black wire from the cig lighter "bowl" runs to a sheet metal screw somewhere on the firewall.

    If you can avoid drilling holes and using self-tapping screws to provide grounds for your LED strings, so much the better.
     
  12. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    Today I was practicing some of my soldering. I have some junk LED I had from before, so I was soldering some wires to the LED leads. My first couple came out pretty junk, but it got better. Wraped some electric tape around them and heatshrinked it. Looks pretty good. And then I did a mock up on my solderless breadboard. I used 8 AA batteries to power my breadboard. Only major difference was that I have no LM317s yet, so I just used a 470ohm resistor. And the fact that these LEDs are the regualr ones, that have like 1.5 foward-voltage. Either way, I managaed to power up my 3 strings of LEDs in series. Pretty cool stuff ;)
    I looked for some silicon tape, but never found any today. Still very much looking for that guy, but I still got couple more stores I haven't checked.
    Still waiting for my LEDs to come in, waiting very patiently.
    And I picked me up some helping hands. Never opened it up yet, but will definately get sommore soldering time in tomorrow.
    On a useless side note just, me and my buddies watched Evan Almighty tonight. Not my kind of movie, but it was alright. I do like Steve Carrell in The Office. That is probably my favorite tv show now. Good stuff
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Good that you're practicing soldering. The less solder you use while getting the junction "wet" overall with solder, the better.

    Forget the electrical tape; just use heat-shrink tubing. You should have several different diameters of it on hand.
    OK, so three 1.5v-rated LED's in series - what is their rated current? 15 mA?
    8 standard (carbon/zinc) AA batteries in series will generate about 12v. Rechargeables will be less, roughly around 9.6v.

    Assuming you're using carbon-zinc batteries:
    12-(3*1.5) = 7.5
    I = E/R
    15mA = 7.5/R1
    R1 = 7.5/0.015 A
    R1 = 500 Ohms

    OK, so you're close; about 6% low in resistance. If your batteries are fresh, you're putting about 16mA through your LED's. You'd need a different resistor for rechargeables.

    Keep lookin' ;)
    Huh? You should've been using that "Helping Hands" as soon as you got it!
    Check the resistance across your 470 Ohm resistor - if you soldered close to the body of it without a heat sink (the alligator clips of the Helping Hands), it's likely that it changed in value. You absolutely do NOT want that to happen when you're soldering the 60 Ohm resistor to the LM317!

    When soldering, always use a heat sink to reduce the risk of overheating your components; particularly when you're new at it.
     
  14. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    I didn't have the helping hands when I did my first soldering practice. I haven't yet done any soldering to resistors yet because I only have 5 of them for now. I should be getting in my online batch soon though. I'm at work now for the next 3 days so I have no access to my supplies, and no practice for now. I get back home Saturday morning, so hopefully I'll have some packages waiting for me, fingers crossed.
    I do have a question about tapping into the factory wires. I'll make a picture and post my question tomorrow cause it's kinda hard to explain.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Here's an idea for you:

    Remove your accessory/lighter fuse or disconnect your battery before poking around!
    Accessory/lighter sockets usually have a round slip-on type connector in the center rear of the socket. Often, the connection on the socket is threaded. See if you can find a nut that will fit those threads - that way, you can use a terminal lug with a hole through it, and secure it to the back of the socket with the nut. Then just reinstall the slip-on connector. That way, you won't have to cut anything. If your accessory/lighter socket doesn't have threads on it's power connection, you could pick one up at an auto parts place for a couple of bucks.

    The very first item that you should attach to that terminal is a fuse holder! Auto parts stores sell an in-line type fuse holder for about $2. Put your round terminal on one end of the wire, and the other end you'll connect to your LED on/off switch - from the switch, you'll need to make pigtails for connecting your LED spade connectors. Use solder and heat shrink. Try to make it look neat. Don't forget, you're going to need appropriately-sized fuses; as I mentioned before a 1/4 amp fuse will be enough to power a dozen of your LED strings.

    Any time you cut into a vehicle's wiring harness, you're begging for problems to start. The accessory/lighter circuit is a high-power circuit. Plenty of opportunity for arcing and sparking there, not to mention fire! If your vehicle is lost due to a fire caused by a faulty wiring modification that YOU made - your insurance co. may very well balk at covering your loss :eek:

    Oh, my LM317's arrived yesterday - whoohoo! :D Getting busy laying out circuit boards ;)
     
  16. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    I have no idea what you mean by this. I looked at my cigarette before, but don't quite remember threads. The 2 factory wires go into a plug, which is snapped into the back of the socket. I will look again tomorrow. But still not sure what you mean by "terminal lug". I'm guessing that this will allow me to use the positive source without me cutting wires.

    Better to use glass or the regular fuses? This will determine what type of holer I should use.
    "The switch is connected to the to LED spade connectors." LED spade connectors is the LM317?

    OK, so if I do this I won't have to splice into the factory wires, very nice. I was gonna ask how to splice into the wires, but this seems very much the way to go.
    Good for you on getting your LM317s in. I hope mines are waiting for me at home.
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    OK, I guess I should've asked you what the connector to your accessory/lighter socket looked like instead of confusing you - sorry 'bout that. ;)

    If it's a spade-type plug-in, you might be able to find "piggyback" adapters at your local auto supply. Those kinds of adapters have a connection on one side, and two on the other. I bought a kit under the "Help!" brand years ago that had a number of different types in it. Comes in very handy at times.

    By a "terminal lug", I meant something like this:
    [​IMG]
    Incorrect nomenclature on my part; it's actually an "Insulated Ring Terminal"

    But if yours is a spade-type plug, you obviously couldn't use one of those.

    Fuses: I haven't looked at what all is available in the newer style automotive fuses. You want a fuse rated at around 1/4 amp, which is enough to power 12 of your three-LED strings. I know that this value is commonly available in AGC-type cylindrical glass fuses. You research the other kind ;)

    "The switch is connected to the LED spade connectors" - yes, I messed up here. Sorry for the confusion.
    What I meant to say is that first comes the fuse, then the switch, then the multiple pigtails to plug in your LM317's which feed the LED strings.

    Does that make more sense?
     
  18. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    I'm not sure what the spaded type of socket is. But I did take some pics while at work. cig light01.JPG cig light02.JPG
    There are 2 sockets in the dash. One has red and black wires, the other is green and black. The socket has 3 prongs.
    I'm not sure if I will be able to tap into it without cutting, so I'll just ask my question on cutting the factory wire.

    Splice Positive.JPG
    The blue lines are my strings, consisting of LM317 and LEDs. I also forgot to add in the fuse and switch. But how am I supposed to cut into the factory wire? In figure A, another wire is spliced into the factory wire. (I'm thinking this is wrong)
    In figure B, another wire is being used to simply make the facotry wire longer.
    The factory wires are pretty short and difficult to work with, so I'm thinking about adding in an extra foot of wire to both positive and negative, just as in figure B. (Both figures don't show the splicing of the negative wire)

    I also got in my LM317s, 62ohm resistors, and small heatshrink tubing. I noticed that the 3 leads on the LM317 are pretty small, especially the middle one. How in the world am I to solder the resistor to this? :confused: I was not expecting this IC to be this small. Hahaha. It's gonna take a very little amount of solder on it without soldering all 3 leads together. Damn, I hope I didn't buy the wrong ones.
    http://www.fairchildsemi.com/ds/LM/LM317.pdf
    On that page, mines looks like the D2-Pak
    Would it be alright to have these guys in some heat shrink once I get them soldered with the resistor? It's so small and fragile I don't want them coming apart/ breaking.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    OK, I whipped up a crappy drawing of how to connect things up.

    Note that one of the LED strings just has an upside-down triangle at the end - that's a schematic symbol for "ground" - that means to connect the end to a part of the body that's metal, by drilling a small hole and using a sheet metal screw. That's one way to do it. The other way would be to splice into the black wire from your cigar/accessory socket. If you were going to do it the latter way, you would only want ONE connection to the harness, and then pigtail from that.

    Your "Figure A" is closer to the correct way. The socket is designed to carry heavy loads; 10A or more; so you want that wire to not be longer than it has to be. You're using fine wire, besides - it won't carry enough current.

    Note that the fuse is the first thing after the splice, then the switch, then the strings of LM317's & LED's after the pigtail.

    Want to swap some LM317's? ALL of mine are TO-220 case, except I have a few TO-92 package units as well. (the TO-92 case is small, but the leads are about an inch long) I could make use of some of your SMT (surface-mount) devices.
     
  20. self_sponsored

    Thread Starter Member

    Oct 9, 2007
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    Thanks for the picture. It does make things look much easier for me. But what are pigtails? Just one wire branching out to other wires?

    So just as the postive wire, the negative would only have one wire spliced into the factory negative, then pigtailed into other wires? This would be the ground for the strings I don't ground to the chasis, correct?

    Today I was also fooling around with my multimeter on the cigarette plug. It runs at 12.5Volts with the truck off, no keys in. And jumps to 14.2Volts with keys in and truck on. I know this is pretty common knowledge, but I just thought it was pretty cool that one of my sockets get 12Volts of juice even when the trucks off.
     
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