Hello fellow hobbyists!Before I start I'd like to say about 15 years ago I owned an HO Scale model train and loved it! My dad built me a train table in the basement with fake green grass and I was addicted! However, that was 15 years ago lol now I'm 26 and live in an apartment so I don't have room for any trains instead I've started building 1/24 1/25 scale model cars. Which leads me to my question:I'm interested in wiring headlights, tail lights and maybe an interior light to my cars. I'm planning on using 3mm led lights for trains that I found on eBay. My plan is keep the power supply (AAA battery? Watch batteries?) In the trunk, along with a small switch to turn them on and off.I'm wondering if that idea would work? I hope watch batteries will work! The smaller the battery the better! Any suggestions, ideas, websites to purchase everything I'll need or help of any sort would be appreciated !! I've asked this question on model car forums and I get pointed to you train guys I guess you're the pros! Once again any help would be great! Thanks
For lots of information about LEDs, wiring, power, etc, checkout www.ngineering.com or www.richmondcontrols.com
I don't see any reason your plan won't work, depending on what voltage your ebay LEDs are designed for. A lot of model railroad LEDs are designed for 12 volts or more, which you'll have trouble doing with batteries.....you'll need 8 1.5 volt AAA batteries to get 12 volts, which is OK, but probably a tight fit in the trunk of a model car. You may have to find some lower voltage LEDs. Watch batteries will work to light LEDs as long as you match voltages. Taking a page out of the model train book, you could use a magnetic reed switch hidden in your model.....you then simply pass a magnet near the switch to turn the lights on and off.
Most LEDs have a forward voltage of between 2 and 3.5 volts. But, because most of us have 12V available, they come with the proper resistor to limit the current. Remove that resistor, and replace as appropriate, and the LED will work. The key to wiring cars will be which LEDs are used, which batteries are chosen, how bright each LED should be (desired current), etc. Even at 1/25 scale, you might want to consider SMD devices vs 3mm for greater flexibility. And, look into Ngineering's current limiting Power Distribution Board. The Jr version should fit well into one of the cars. Good luck!
I use to build model cars and trucks for competition. I have seen, but have not tried it, using fiber optics in models for dash lights, headlights, taillights, interior. Do a search on ebay and see what you can do with these things. They are small and can be hidden easily in the models.
Just remember that you have to have a resistor in series with an LED. (1000 ohms is a good value) Otherwise it will draw too much current, get hot and burn out. It is not like a light bulb. Also it has a "+" and a "-" so polarity is important. Wire it backwards and it does not work.
You can power most LED's using a "coin" battery something like a CR2032. I have not tried to power more than one at a time with a CR2032, but it could work, but how long I don't know. Gary
An LED alone is like 2 PN junctions in series. Each PN junction will drop 0.7 volts. So an LED alone will drop 1.4 volts (0.7v + 0.7v) If you use a power supply with any more voltage than that you must use a resistor or some other voltage limiting device to drop any extra voltage or your LED will burn up. LEDs made to work with 12 volts already have a resistor in series with them. The choice of resistor is to control the current passing though the LED. All LEDs have a current rating. Using ohms law you can figure the proper resistor to control (limit) the current going though the LED. Never run any LED with out a current limiting device (ie. resistor). Also each LED needs its own resistor. Do not connect multiple LEDs in series or parallel and try using only one resistor. Do it right the first time and you will not have any problems.
Hope the below might help. Store the link in Favorites. Check his home page for many other good links. http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm Rich
Different LED's have different voltage drops, for example, white LED's have a voltage of greater than 3 volts. I agree that you shouldn't have LED's in parallel running off a common resistor, but there is nothing wrong with having them in series as long as your source voltage is high enough. In fact, it can be a good way to reduce current draw. For example, running two LED's in parallel each at 10 ma would draw 20 ma, but running them in series would only draw 10 ma.
The capacity of a Maxell CR2032 3V coin battery is 220 mAh. So if you configure your LED circuit to draw 20 mA, the battery should last around 11 hours if you run it until it is fully depleted. If you are drawing 40 mA, the coin battery will last around 5.5 hours. There are 3.6V rechargeable lithium-ion coin cells. Their capacity is only around 120 mAh but they are rechargeable so you can use them over and over. If you go to a larger form factor, rechargeable 3.7V lithium-polymer batteries intended for small R/C aircraft have a 500 mAh capacity. They measure 80 x 18.5 x 8 mm (3 x 0.8 x 0.3 inches). Drop down to 300 mAh, and rechargeable 3.7V Lipos are only 30.5 x 20.5 x 6.2mm (1.2 x 0.8 x .25 inches). They might fit in a 1/24 trunk. - Jeff
OK. It has been about 25 years since I was in electronics school and back then they didn't have any LEDs other than red and green. I guess things have changed. I still stand by my recomendation that every LED have its own resistor and that should be the way current is limited to them. You might get away with wiring some in series and using only one resistor, but if you do not want any problems (and resistors are cheap) use one resistor per LED.
The only "problem" with wiring them in series is any LED's in one series will be driven at the same current level, but if you have multiple LED's that you want to drive at the same current and have a high enough source voltage, especially if you have a lot of LED's, then it really doesn't make since not to wire them in parallel groups since it reduces your power needs and excess heat generation. This isn't something people just "get away" with, it is good design practice and common in many areas. Take the LED strip lights that a lot of modelers have started using, for example - most of them are designed to run off of 12 volts and the LED's are wired in groups of three, with each group being wired in series with one resistor. The same light strip with the same light output, with each LED wired separately with it's own resistor, would draw three times as much current and actually produce more than three times as much wasted heat. For a really extreme example, look at LED Christmas lights. You can get a 35 LED string that has all of the LED's wired in series that draws 2.4 watts. If that same string where wired in parallel, it would draw 84 watts, with the vast majority if that wattage being wasted in heating up resistors instead of producing light. Here's an example more applicable to the original post: He's interested in using coin cells and lighting headlights as well as other lights. For the headlights, he will need white LED's, most of which have a voltage drop of about 3.2 volts, which means to use coin cells he will need at least two to have enough voltage. If he uses red and amber LEDs for taillights, then the 6 volts of the two batteries would be enough to run them in series groups of two, which would be less current draw and a longer run time from the batteries.
