I am trying to get a 1.5 Miniatronics bulb to work off my FL4. I know the FL4 is 12V, I have an LED working on it right now. I need to step down the power to power the tiny 1.5 V bulbs to run some beacons. I have tried a 750, 680, and 1k resistor and get nothing, no light at all. I get a very,very dim light with a 470. These are all 1/2 watt resistors. What am I doing wrong? Even if I hook it up to a 12V source not through the FL4, I am still getting the same results
What is the current rating for the bulb? That will define the minimum resistance you need. In general, take the 12 volts and subtract 1.5 volts which leaves 10.5 volts. Divide 10.5 by the current rating (in amps) and that will be the mathmetical resistance needed. Choose a standard resistor value that is close to that number. Larger values relative to that value will dim the bulb, you will have to experiment to get the brightness you desire.. Also take 10.5 TIMES the current rating (again in amps) and that will be the power that is being dissipated. Your resistor has to be rated to handle at least that much power. Bigger is better and safer (runs cooler to the touch) Lyle
These are 30 milliamp bulbs. After doing some searching, I came up with 330-350 ohm resistors. What do you think?
The final value will depend on track voltage as well as what looks right to you for 'dim'. For 30mA bulbs, I use 390 ohm, 1/2 watt resistors most of the time for a well lit bulb. The defined track voltage for DCC is supposed to be a bit over 14 volts so I usually use 12V as the value across the resistor for my calculations (rather than 10.5V). If your power supply voltage is lower , you'll need to lower the resistances a bit compared to my calculations. In my case, 12v/.030A = 400 ohms, and 390 is the closest standard value. Standard 5% values above that (to be dimmer) are 430, 470, and 510 ohms. You'll have to test to see what looks right for you.If you need to find values that fit in between the above 5% values, you'll need to locate 2% or 1% toleranced values which include values between the 5% values. The power rating for all choices will need to be exceed 12v * .030A, which is .4 watt, so most if not all of the resistors will need to be 1/2 watt. Lyle
Why not just use the classic 6-diode circuit? I have this in all my locomotives on my DC layout and it gives "constant lighting" as well. http://www.mrollins.com/constant.html (or Google "6-diode constant" for more) But if you're on DCC, disregard this. I'm waiting for Bluetooth Direct Train Control to come out. John
I got some 330 1 watt resistors, and did a test just to see if they would light, and they did. I havent done a long term test on them yet, just a quick hook up, and they light up like they should. To make this more interesting, I guessed these were 30 MA bulbs based off of Minatronics website. When I got another package of them(since I burned up most of the ones I had trying to figure out why they wouldnt work), the package says 15 MA. Go figure
no offense, but what you are doing wrong is trying to treat a light bulb like a led. LEDs work on current, so you calculate a dropping resistor to limit the current. lamps work completely differently, they work on voltage, and in order to dim one, you really need a regulated voltage. (To make matters worse, lamps change their resistance as they change brightness) you can eventually find a resistor to dim a lamp, but you need to have one that is correctly selected, and you basically have to measure the current the lamp is running first to get a ballpark. then you have to figure how much you want to dim it, and also realize that half voltage does not make it half bright. Try dropping the voltage only 15-20 percent, it makes a lot of difference. Once you have used Ohms law to calculate the resistor value in ohms, then calculate the wattage needed... the square of the current times the resistance times 2 will give you a proper wattage (if you try to run a 1/2 watt resistor at 1/2 watt, it will be hot enough to burn you and melt plastic, that's the times 2) If you have not figured out by now that you should stay with LEDs, then I've done a poor job ha ha! Greg
I stayed out of this for a while. A 1.5V incandescent is a "constant lighting" bulb. John mentioned it, altho I have used 4 diodes. A diode drops .75V. Two in series drops 1.5V. IF you want to not "push" the limits and have 1.5V to a 1.5V bulb, add a third diode to drop 2.25V You put two (or three) in series, all bands in one direction, ANOTHER two or three in series PARALLEL to the first set, all bands in one direction, but reversed of the first set. Place this assembly in series in one motor lead. This give the voltage drop of 1.5V or 2.25V across the set. Now, solder your bulb leads one to each end of the assembly. When you start moving your loco, the voltage drops across the didoes before the motor starts turning. You now have full intensity as the loco starts, never gets any brighter. But, it requires a load (like a motor), and if your application is something without load, no idea. I have no idea what an FL4 is, other than a "VARIETA FLOOD LIGHT Application:Accent lighting for exterior retail, commercial and hospitality environments", or "the FL4 (until 2012 FR4) is a regional rail route. It forms part of the network of the Lazio regional railways (Italian: ferrovie regionali del Lazio), which is operated by Trenitalia, and converges on the city of Rome, Italy" .
