LEDs in truck

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

  1. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    Hey howzit going everyone. My name's Kell and I'm from Hawaii. I came here to try and get some help with my first electrical project. My knowledge is very minimal and I just read the Electronics for Dummys book but I am still very new to the exciting world of electronics. I am apart of a Nissan forum, and have been getting help from there, but I also want to get advice from the experts just in case. I have a truck and I want to put LEDs in it in various places.
    1) If I have an extra cigarette lighter that I don't want to use, can I just use the positive and negative wires from it and hook up my series of LEDs? Is the voltage rating for cigg lighters in a truck a little bit higher then 12V?
    Does this look ok to do? Or maybe I should run 2 LEDs off of a larger resistor. But it all depends on how many volts I am getting from the lighter. Those lights are rated at 3.2 foward-voltage, and 20mA foward-current.

    2) I have a rocker switch that turns on a cargo light for my truck bed. It can stay on forever, as long as there is battery power going to it. But I can also turn it on with no battery power, and it will light up for about 5 minutes, and then auto shutoff. I want to have LEDs that will have the same properties as my cargo light. Is this possible, and if so, how can I tap into it? And I'm guessing there is 12V going to this cargo light rocker switch, but I'm not sure.
    Much mahalo for your help in advance. Sorry for my lack of knowledge. Your time is much appreciated.
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    The voltage in your cigarrete lighter may reach 18V when the car is moving, but the normal is 13.5V. You can run 3 LED's with no problem. Just use a 470Ohm resistor. However, I would advice you to use series of two LEDs, so the brighness won't vary that much. In that case, a 680Ohm resistor would be fine.

    There is no LED with such property. My immediate idea is to use an OR gate with one input connected to a 555 timer and the other input analysing if battery has enought power (maybe using a comparator). Notice that if you use the standard 555 timer (LM555), you will have to use TTL. My idea is to use the CMOS version LMC555 and use a CMOS gate, since they have better characteristics.
  3. niftydog

    Active Member

    Jun 13, 2007
    Don't some trucks run at 24V? Measure before you connect your LEDs!
  4. SgtWookie


    Jul 17, 2007
    US Military vehicles use 24v DC electrical systems ... actually, they're called 24v like folks call standard civilian vehicles 12v systems. In actuality, the military batteries measure around 25.4v when fully charged; when the vehicle is running the generator/alternator is putting out nearly 28v.

    As I mentioned, a civilian motor vehicle will usually use a 12v system; with a charged battery it will measure more like 12.7v. When running, the vehicle's charging system may put out from 13.7v to 14.5v, sometimes even higher, depending upon the charge depletion of the battery, electrical loads, condition of the wiring, etc.

    LED's are very sensitive to over-current; you will shorten their life drastically if you happen to run more current through them than they are designed for. Additionally, I've found that they often fail in a "shorted" mode; if you have LED's strung together in series then one shorted LED will rapidly exceed the rated current for the remaining LED's in the string. The result will be little blobs of molten plastic with smoke leaking out of them! :eek:

    LED's light output is also linear with respect to the amount of current flowing through them. So, to make them brightest, you want to run them near their rated output, correct? Well, you have a problem - your vehicle's battery might measure down near 12v when you've left the lights on for a while, but when you crank it back up, you might exceed 14.5v on starting! That's quite a bit of difference in voltage; 14.5v = 12v * 120% (approx) - so if you just put in a resistor high enough to protect your LED's at 14.5v, they'd look kind of dim at 12v. What to do? :confused:

    You're in luck! There is a 3-terminal voltage regulator being made that can be easily rigged up as a precision current limiter by adding just one resistor. :cool: This regulator is the LM317. They're available online everywhere, and even at your local Radio Shack (albiet more expensive there)

    The LM317 has three terminals, Vin (which goes to power), ADJ and Vout. You connect up a correctly-sized resistor (R1) between the Vout and the ADJ terminals (value between 0.8 Ohms and 120 Ohms inclusive) and your selected current is available from the ADJ terminal - providing there is enough voltage (under 37 volts) to provide it.

    Iout = 1.2/R1

    That is, the output current is equal to 1.2 divided by the value of R1.

    So, if you hook up a 60 Ohm resistor between the Vout and the ADJ terminals, feed 12 to 37 volts to the Vin terminal, you will get 20mA regulated current from the ADJ terminal. (It MUST be AT LEAST 60 Ohms - if not, use the next larger size resistor, or two 120-ohm resistors in parallel, or some combination that measures at least 60 Ohms) You could hook up just 1 LED, or two, or three in series - the LM317 will adjust the voltage output to raise the current up to 20mA, up to the maximum voltage available. There's more good news - if one of your LED's in a string gets shorted out, the LM317 will immediately drop the current so that the remaining LED's don't get zapped.

    Now, you might be tempted to think - "Hey, this is great - how about paralleling some series strings of LED's and change R1 lower" - well, your LED's are not identical and they're going to draw slightly different amounts of current. And if you're parallelling several LED strings, you could wind up with a string melted down. Even worse, if one of the strings "broke" somewhere (wire came loose, LED burned "open", etc.) the LM317 would increase the voltage to bring the current back up - and fry the rest of your strings!

    Electronics doesn't get a whole lot easier than this ;)

    Reference: National Semiconductor, Application Note 181, October 1975

    As far as your other application - yes, that can be done too. But my fingers need a break.
  5. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    Aloha all, and thanks for the advice guys. It's nice that there's a few ways to approach electrial projects. The LM317 seems like a very good way to hook up my LEDs, due to the flucuations in my voltage. I'm kinda confused about having the 60ohm resistor (or greater) between the Vout and Vadj. You said either a 60ohm resistor, or two 120ohm resistors in parallel. Why not just use one 120ohm resistor? Is 120ohm smaller than 60ohms?
    Wookie, you mentioned something about me not using too many of these series of 2 or 3 LEDs off one one 12V line? How many series do you think I would be able to to run in parallel off one 12V line? I was thinking about running 3 series, so I would have 6 or 9 LEDs to use. Would using bigger wire (18ga. maybe) enable me to run maybe 5 or 6 series off of the orignal 12V line without fear of melting stuff?
    I just spent $80 today buying circuit stuff to practice and eventually do my truck project. Breadboard, wires, multimeter, battery holder, cheap LEDs.
    Either way, I gotta wait for my good LEDs I ordered online to come in.
  6. thingmaker3

    Retired Moderator

    May 16, 2005
  7. SgtWookie


    Jul 17, 2007
    The reason I stated that you must have at least 60 ohms between the ADJ and Vout is because if the resistance is less than 60 ohms, the LM317 will put out more than 20mA, thus shortening the life of your LED's.

    For this circuit:
    Iout = 1.2/R1
    Iout = 1.2/60
    Iout = 0.02
    0.02A = 20mA

    You need exactly 60 ohms across the Vout and ADJ terminals to output exactly 20mA. Trouble is, 60 ohms is not a commonly available value.
    Let's say you had a bunch of resistors in your "treasure box" that were marked 1, 2.2, 10,15, 22, 33, 39, 47, 51, 68, 82, 100, 120, 150, 180, 220, 270, 330, 390, 470, 510, 560, 680, 820, 1k, 1.2k, 1.5k ... Ohms - these are values commonly available in assortments. Notice that they skipped right over 60 ohms!! What to do?

    Well, you could try using a 10 ohm and a 51 ohm in series, that'll get us close.
    In series, resistance is additive
    10+51 = 61
    Iout = 1.2/61
    19.67 mA
    See, just that 1 extra Ohm knocked the current down by 0.33 mA
    But notice that you also have some 120 ohm resistors in there. Resistors in parallel if they are EXACTLY equal in resistance you can calculate by Resistance/#ofResistors (if they're not EXACTLY the same, formulas are on the pages Thingmaker posted.)
    120/2 = 60. Look at 180 ohm resistors; 180/3 = 60.
    BUT! Resistors have a tolerance. They might be 1% tolerance, 5%, 10%, or even 20%. Those you get in assortments are generally 5%. What happens if your resistors are 5% lower than they're marked?

    60 Ohms becomes 57 Ohms
    Iout - 1.2/57
    Iout = 21.06mA (approx)
    You've just exceeded the rating of your LED's.

    In this application, it's important to measure your resistors with a precision digital multimeter (DMM) to ensure they're the right value.

    Your LED's are rated at 20mA @ 3.4v.
    For now, assume that the LM317 will drop at least 1.5v across itself (the actual voltage drop may be slightly more or less.)
    3.4v * 3 + 1.5v = 11.7v - as long as you supply at least 11.7v to the LM317, three LED's in series will get a full 20mA supplied to them.

    Let's talk about your accessory circuit. Usually, these are rated to supply over 5 amps of current - but check your manual to be sure.
    Each string of LED's with it's LM317 current limiter requires 20 mA
    So, 5A / 20mA = 250 - will 250 strings of 3 LED's be enough? Or were you hoping to be seen from Jupiter? ;)

    20 mA is a very small amount of current, so you can use small gauge wire for your string. However, your big problems are heat, vibration and corrosion. Vibration will cause your wires to waggle around, and eventually break due to metal fatigue. Use finely-stranded wire, and tie it down to your frame or something solid. Those little nylon zip-tie things work great. Something non-standard that you could use is aluminum HVAC tape for repairing A/C ducts; that stuff stays stuck on forever, and as a bonus has a shiny surface to reflect heat. Speaking of heat, that will deteriorate your insulation over time. Keeping the wiring away from heat sources (like exhaust pipes, your radiator, etc) will let your wiring live longer. Corrosion is perhaps your biggest enemy there in the Aloha state. That salt air is great to breathe, but it wreaks havoc on exposed metal surfaces. Use heat shrink as you've planned for all of your connections.

    There's a product out there called CorrosionX; it was developed for the Navy to help preserve aircraft deployed on aircraft carriers. It's available in spray cans. It's not cheap, but it works great. Used it to treat the entire airframe and wing spar of my Dad's Cessna 150. If you have any exposed electrical connections, you can use a blast of that stuff to protect from corrosion.

    Well, you absolutely need a good meter. It's best to have two; one digital, one analog. The digital multimeters (DMM) are VERY accurate, but they're hard to use when monitoring changing voltage or current levels; the numbers go all over the place. That's when the good old VOM (Volt-Ohm Multimeter) comes in handy. The needle will flicker around, showing you what the trends are.

    I highly recommend the "Electronics Learning Lab" that Radio Shack sells

    It's $65, but it comes with a GREAT breadboard:
    along with two workbooks; "Basic Electronics" and "Digital Logic Projects", components, jumper wires, all kinds of stuff. The books were written and breadboard designed by Forrest M. Mims III, and I can't say enough good things about this kit. Actually, calling it a "breadboard" is selling it far short; it's more like an integrated electronic workbench.

    You need that kit, six "AA" batteries to power it, and a DMM (you don't need a fancy DMM, either; I have a couple DMM's I picked up from Harbor Freight for under $4 each that I like just fine.) Unless you have immediate plans for the other stuff you bought, consider returning them and going with this kit. I'll bet your "shopping list" will change considerably after spending a week or two with it. ;)
  8. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    Whew, I'm diving deeper and deeper into electronics by the day. I just wanted a simple understanding to do a little mod to my truck, but this is pretty cool.
    The more I think about this, the more I get confused. So If I don't mind totally eliminating the use of a ciggrette lighter, I'm pretty sure how to wire it that way. But I'm unsure of how to wire it in a way to keep the cigarette lighter. Such as if I want to hook up LEDs to come on with my interior lights (Dome Lights).
    As for the LM317, I'm still a little uncertain how this guy works, and how to hook it up. Does the positive or negative wire go to the Vin? Does it matter?
    I need to use one of these guys in every series?
    I have to put the resistor between the Vadj and Vout?

    I made another painted schematic, but it was wrong. Damnit, I'm gonna make one tonite later on. I'm writing one on paper much easier.

    I'm not sure on the term of grounding. Having this hooked up in parallel is having it grounded already?

    And as far as slicing into my factory wires goes,
    1) Is stranded wire better? I was thinking about going for solid.
    2) Are those Scotch Locks anygood for long term slicing? Or should I just go with the good old way; expose wires, twist together, electrial tape, and heat shink.
  9. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    For this schematic, I will be using R1, R2, and R3 as reference points to each parallel wire, and not resistors.
    Suppose that R3 is the original plug for my ciggarette lighter.
    If I run my LM317, resistor, and my 3LEDs at points R1 and R2, is this correct? I orignally thought this was correct, but all of a sudden I'm thinking this will mess up the cigarette lighter. My brain is getting tired. Please help
  10. thingmaker3

    Retired Moderator

    May 16, 2005
    You want them in series, not parallel. Check the links I gave in my earlier post.;)
  11. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    I checked out the links you gave. I printed out the first one the other night.
    I am wiring the 3 LEDs in series. But I am putting 3 "strings" of LEDs in parallel. Isn't this the way to do it?

    So R3 is the ciggarette plug. The top wire, (points 1-4) are the positive factory wire going into the positive terminal of my cig plug. The bottom wire, (points 8-5) are the negative factory wire going into the negative terminal of my cig plug.
    Across wire 2-7 is going to have a LM317, 60ohm resistor, and 3 LEDs.
    Across wire 3-6 is going to have a LM317, 60ohm resistor, and 3 LEDs.

    The 3 LEDs are going to be in series. But the two "strings of 3 LEDS" (wires 2-7 and 3-6) are going to be in parallel with each other. The two strings of 3LEDs are also in parallel to my cigarette lighter..... Is this the correct way of saying this?
    Would this be a correct way of wiring LEDs without messing up the function of my cig lighter?

    I am planning on wiring 3 strings of 3 LEDs, but for this schematic, I only have two strings.

    I'm sorry if I'm confusing/ irritating you guys. I really do appreciate your help and expertise. It's probably like Michael Jordan trying to talk basketball with some kid who never did play any sports ever. You guys being Jordan, me being the kid.
    Or Bush talking to some kid about politics. You guys being the kid, and me being Bush:eek:
  12. SgtWookie


    Jul 17, 2007
    OK, let's take a step back ;)

    I've attached a drawing similar to the original sketch you posted, but with the LM317 connected in as a current limiter. I made a schematic inset, so that you can compare how the symbols represent the real items. The drawing and schematic represent 1 string.

    The 60 Ohm resistor is the exception. You might be able to find a precision 60 Ohm resistor at an electronics shop if you're on Oahu; not so likely on the other islands (look for shops near the military bases) but more likely than not, you'll be making an equivalent resistor using two or more in some combination of series/parallel. Two 120 Ohm resistors in parallel would be a good bet, but you will have to measure your resistors and let us know what values you have compared to how they are marked.

    NOTE: Resistors can change values if you overheat them when soldering! Practice soldering using some scrap pieces of wire. A good solder joint is clean, has a shiny surface, and you can clearly see the outline of the wire. It takes practice. Clean your parts with isopropyl alcohol just prior to soldering. Use a low-wattage pencil-type soldering iron, Sn63 or 63/37 tin/lead solder (solid or rosin core) and flux; NEVER use acid-type (plumbing) flux. Clean off all flux residue after soldering using the isopropyl alcohol and "acid brushes". The alcohol is available at your drugstore; try to get 90% or better. 70% has a lot of water in it. Try to avoid getting it on yourself. Isopropyl alcohol is flammable, and the flame is very hard to see; use appropriate precautions.

    I store my "treasure box" resistors in "coin envelopes" - you can get a box of them at your local office supply stores. I put just one value of resistor in an envelope, and mark that value using a pencil on the side opposite the flap, along the top edge; and keep them in order of ascending resistance. This makes them very easy to find and compact to store.

    Note that the LM317 has Vout on both a pin, and the mounting tab. You must not let the tab or any of the pins touch metal on your truck's body, as it will cause a short circuit.

    These IC's are usually mounted on a circuit board and have "heat sinks", or heat radiators physically connected to them for high current applications. However, 20mA is such a small amount of current that you could cover the whole thing with heat shrink tubing and not worry about heat build-up.

    One important thing I neglected to include - a fuse!

    Fuses protect your wiring and circuitry by self-sacrifice. If something is wrong, they burn up instead of your wiring and comparatively expensive electrics/electronics.

    For your application, a fuse rated 1/4A @ 32V would be more than sufficient.
    1/4A = 250 mA; more than enough current to run 12 such LED strings in parallel.
    For each string, you would connect the Vin terminal of the LM317 to one side of the fuse, the other side of the fuse goes to your power source (like the dome lamp) and the other end of the string to chassis ground or the negative battery terminal.

    The fuse should be as close to where you're getting your + voltage source as possible.

    Is this clear enough?
  13. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    Thanks, that picture helps out a bunch. I think I'm getting real close to start getting this guy started, but still waiting on my LEDs to come in, which could be as much as a week more. But either way, I never did solder before, so I'm gonna go Radio Shack and get me a pencil and some soldering wire and practice this weekend.
    Still question on the wire I should use. Stranded or solid? I went to Home Depot to check some out, but they didn't have anything smaller then 16gague.
    If I wanted to have a rocker switch to manually turn these lights on/off, I would just have to wire the switch in series before/after the strings of LEDs. I seen some switches with 2, 4, and 6 terminals.
    You also said something about how I wouldn't have to worry about heat problems with the IC because it is only running 20mA. But isn't it going to be running 60mA, cause 20mA muiltiplied by 3 LEDs?
    And one more thing. So if I wire 5 or 6 strings of these in parallel with my cigarette lighter, the cigarette lighter will not be altered?
  14. SgtWookie


    Jul 17, 2007
    OK, as long as you're waiting on your LED's, you might consider ordering some LM317's from the Web as well - yes, you can buy them at Radio Shack, but they'll cost you around $2.50 each (including tax) - and you need three of them; I'm sure you'll be adding more in the future. That IC is also great for building power supplies; if you start getting into electronics, one of the first things you'll need is a power supply. You might also want a battery charger. Guess what - the LM317 can be used for charging batteries, both automotive and rechargeable NiCd batteries. I have a number of projects I'm working on involving charging batteries and power inverters; I just bought 50 of those IC's for $15 (including shipping) from an auction website. Get some extras; you can sell some of them to your friends who want to do similar stuff.
    You definitely want stranded wire; the finer the strands, the better. Solid wire should only be used on circuit boards, or in places that absolutely won't move (like in house wiring.) I don't know if you have any surplus stores around; we have a great one here in Orlando that sells a lot of mil-spec surplus wire. It's teflon coated with really fine strands that are silver-plated; made for harsh, high-heat high-vibration enviornments like military aircraft. But if you don't have a store like that there, this should work just fine:

    a 90-foot spool of 22 gauge stranded wire, red insulation, $4.99. Cheap, and should be enough to do all three strands.

    Make sure you get 63/37 solder. You CAN use 60/40, but 63/37 is better. That particular ratio of tin to lead is "eutectic" - that means when it's cooling down, it goes directly from a liquid state to a solid state, with no "plastic" state in between. If you move your connection while it's cooling in the "plastic" state, you'll wind up with a gray-looking ugly dull solder joint, that will not conduct electricity well at all, as long with being physically weak.
    You would only need a SPST switch - that is "single pole, single throw". Usually, you would want to put the switch in the circuit right after the fuse. That way, when the switch breaks the circuit, everthing after the switch becomes "cold" - no power anywhere.
    No, in this case, we are running three LED's in SERIES. Think of current as water in a pipe; your power switch is the main shutoff valve, the LM317 is the pressure regulator valve, and the LED's are like the pipe taking a steep vertical climb. The ground is like the end of the pipe. All of the water (current) flows through all of the devices in the string. Along the way, the pressure (voltage) gets cut off completely, regulated, or consumed. By the way, a column of water about 7'9" tall exerts a pressure of about 3.4 PSI at the bottom - so this correlates directly to the analogy of voltage = pressure, when you consider that each of your LED's is rated 20mA at 3.4v.

    Actually, Radio Shack sells a pretty nice adapter for the cig lighter.
    A bit pricey at $9, but it's much better than most I've seen. Besides, when you build more stuff later on, you'll have the option to plug things in using banana jacks or wires; and if something goes wrong, you can just yank the thing out of the lighter socket without damaging anything or making any modifications to your vehicle. You'll be better off that way. Won't need a switch, either ;)
  15. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    OK, this is good. Everything you said makes sense to me, except one thing. The cigarette lighter. So the banana jack adapter would be pluged into the cigarette socket, and then one would have a positive and negative place to add wires or banana plugs?
    If this is correct, it seems like an easy way to add stuff, but the aesthetic value is pretty low due to having that plug and wires visible.
    Sorry if I was wording it wrong, but I wanted to know if my cigarette lighter socket would still be functionable if I hooked up 5 strings of LEDs in parallel with it.

    Other then that, I'm about to order a lot of 50 LM317s from eBay, and gonna go check out Ace Hardware and Radio Shack right now for some supplies/
  16. SgtWookie


    Jul 17, 2007
    That was the idea. It's a handy way to try stuff out without actually cutting into your wiring harness. Avoid cutting if you can; plug into existing stuff instead. You're new at this, and I would hate for you to mess up your vehicle's wiring. Take a look at your fuse block; you might have an unused slot with a 1/4" tab next to it that you could plug a connector into. That way, you wouldn't have to buy a fuse holder - just get a very small fuse (1A or less), plug it in and use a connector crimped to your wiring.

    Well, the cig lighter adapter would give you a great way to test stuff without making any cuts or changes in your wiring. It's also great to hook up stuff like CB radios (Truckers are like road gods - they know where all the cops are, and where all the routes are to avoid the accidents, the best places to get good eats, and the cheapest places to buy fuel.)
    Absolutely, as long as you don't goof up the connection to it!
    The cigarette lighter/accessory outlets I've had in my vehicles generally are fused at 15 to 20 Amperes from the factory. If your cig lighter/accessory fuse is 20 amps, and you're hooking up three of these 20mA strings of LED's, you will have 19.94 amps left, or 99.7% of your original capacity. Heck, even if it only had a 5 amp fuse, you'd still have 98.8% capacity left.

    In order to be consuming a full 20 amps with your 3-light strings, you would need 1000 strings. That's 3,000 LED's. I suggest you don't do that; the neighbors would be calling the fire department all the time to put your truck out, not to mention the complaints we'd get from the Martians. :rolleyes:

    OK, I don't like to mention secondary-market suppliers by name on this site, unless they are PAID advertisers. I feel that is bad manners.

    Ace Hardware has some good stuff, but you have to shop carefully. Much of it is overpriced, and some of it is just plain junk. But they do have customer service and a broad selection, and that's why you're paying the higher prices. If it weren't for my local mil surp store, I would be spending a LOT more time at Ace Hardware. Big Orange and Big Blue don't have the selection of hardware like Ace does. That's what's keeping Ace alive.

    Get some of your buddies on board with the LM317's beforehand - unless you have that "phat wallet" thang goin' on. ;)

    DO pick up that kit I mentioned - you will learn a LOT about electronics.
    Forrest M. Mims III has a way of breaking things down "Barney style" that doesn't really seem Barney-esque - it just makes sense.

    It'll be the best $65 you ever spent as far as electronics goes, I'll guarantee it.

    While you're buying stuff on the web, pick up Forrest's book, "Getting Started in Electronics" - you can order it right from him, here:

    Forrest Mims III is da man ;) There are TONS of boring electronics books filled with formulas and excruciating minutae, but Forrest gives "everyman" a leg up in electronics. No, his books aren't perfect; I've caught a few mistakes here and there. That makes it even more fun. You won't find an easier or more fun way to learn this stuff than Forrest's books.

    Oh, and as far as the 60 Ohm resistor:
    68 Ohms and 510 Ohms in parallel = 60 Ohms.
    Strange, but true. There are many more combinations. That would be a worthwhile list to post on the site, but it would be a rather long post.

    I wonder if the Administrator would object to having such a resource available?
  17. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    The cigarette lighter with the banana jacks does seem like an easy way to wire stuff without having to go behind the dash to find the factory wires. How does it run the + and - terminals coming off the adapter? It's like hooking it up in parallel?
    I found a site that has a PDF form of the workbooks from the Mimm's Lab. It definately looks like a good setup. I'll go look at my Radio Shack today. The online site it was at the Maui stores, but the price will most likely like 5 or 10 dollars more.
    For Mims "Getting Started in Electronics" book, I'm gonna check the library on Tuesday because they are closed Sun/Mon.
    I checked for some resistors, but no 60ohm or 68ohm I think there were 20ohms, but wiring 3 of them in series would be a waste. If there could be a post of other combos that equal 60ohms of resistance that would be very nice. I'm looking online, and found a mixed bag of resistors. I found some 68ohm and 47ohm. One seller has a lot of 13,000 resistors with 60 different values!! Rated at 1/4watt, for 20$ shipped. I wouldn't use them all, ever. But I wouldn't have to buy anymore resistors ever. Hahaa. So I might just end up buying one of these mixed bags.
    I got 50 LM317s heading my way also from online.
    For the running my fuse, I'm sure there's a spare outlet, so I gotta check my fuse box.
    Thanks again for all the help and info. I really do appreciate it
  18. self_sponsored

    Thread Starter Member

    Oct 9, 2007
    I just found a seller that sells packs of 100 resistors, for like $3.50 shipped. He has 56ohm and 62ohm. The 62ohm looks better, cause better to have my LEDs a tad bit weaker then have them blown. But these ones at at ±5%. So they might be 58.9ohm-65.1ohms. At 65.1ohm, you think that'll make a huge difference?
    I would rather have to just wire in one resistor equal or close to 60ohms, than to wire in two or three larger-ohm resistors.
    And another pack is 1/4 Watt ± 1% Resistor Kit 100ohm,220ohm,330ohm,470ohm,560ohm. 100 pieces of each value. I like the ± 1%, but too bad none are 60ohm.
  19. SgtWookie


    Jul 17, 2007
    Yes - actually, it's just changing the form of the connection. For your LED's, you would only be hooking up the end with the LM317 to the red + terminal, as the other end of the "string" would be connected to the chassis somewhere using a sheet metal screw and a crimp-on connector. But for testing, you could just hook the other end (ground) up right there.

    You know, you can figure that out for yourself?
    Resistors in parallel are calculated as:
    Rt = 1/ (1/R1 + 1/R2 + ... 1/Rn)
    Or for just two resistors:
    Rt = (R1 * R2) / (R1 + R2)

    Getting a "grab bag" of resistors that big would certainly give you lots of practice on recognizing resistor color codes! :D You'll be sorting resistors until your eyes bleed! :eek:

    I did something similar, but I bought an E24 assortment that had 169 different values, 50 each on tape, grouped by range, 8,450 total. They came in bags like this:
    wound up at $35 and change including shipping. Yes, it was an auction. Easier to keep track of what's what when they're on tape, and in labeled bags ;)

    Good deal. In case there is no spare "aux" fuse (sometimes they don't include a fuse clip if it's not used) you can get in-line fuse holders for a couple dollars most anywhere.

    A word about regular electrical tape - I don't like it. After it's been exposed to heat for a while, the adhesive gets "gummy" and the tape starts peeling off, leaving your bare wires exposed. Sometimes you can't use heat shrink without cutting a wire in two. Instead of cutting the wire, look for some silicone tape; it's usually black with a narrow green or blue stripe running down the middle of it. It's used on military aircraft wiring. It sticks to itself. You might find it at your local auto parts store marketed under the "Extreme Tape" brand.

    It takes a bit of practice to use; you have to keep it stretched while wrapping it around the wire. You overlap the edges just enough to cover the stripe running down the middle. When you get to the end, it's best to hold it in place with a nylon zip-tie so it won't come unraveled. It will eventually "cure", and won't come off without a lot of effort. You need to have your hands clean when handling it; finger oils or automotive oil/grease will prevent it from bonding properly. Keep the unused tape in a sealed plastic bag like a Ziploc.
  20. SgtWookie


    Jul 17, 2007
    Iout = 1.2/R1
    Iout = 1.2/62
    approx. 19.35mA

    That's fine - remember that those resistors are most likely 5% tolerance. That means that some of them may measure as low as 58.9 Ohms! That would put you at about 20.37mA - probably not terribly life-threating for the LED's. However, you should test each one before wiring it up.

    Oh, on your next trip down to the Shack, pick up some alligator clips, or test leads with alligator clips on them. Use them when you're soldering; put the clip between the component and where you're soldering the leads. This will help a great deal in preventing heat damage, besides just holding the stuff in place while you're juggling solder and soldering iron.

    R.S. used to sell a little "helping hands" rig - it had a built-in magnifier and a pair of alligator clips on a flexible stand. I found it pretty doggone handy. You can find them elsewhere for less, but considering where you are, your options are probably somewhat limited.

    Were I in your shoes, I'd try finding a HAM club and/or join the ARRL (Amateur Radio Relay League) - they build all kinds of cool stuff (including radios, of course) and you can bet they know the best places to get deals on electronic stuff. Besides, as I mentioned before, you'll learn a lot.
    ARRL home page is here: