What do you guys reckon out there in DCC land? I have been using and like 1.5v bulbs in DC locos (with the classic diode constant brightness circuit) for headlights and ditch lights. Anyway I'm getting ready to get my toes wet with DCC and am hearing conflicting stories about 12v and 1.5v bulbs - namely the heat associated with dropping resistors. What sparked the debate in my head was Bill Darnaby's article in June MR - he uses 1.5v bulbs and says if the resistor gets too hot, substitute a higher wattage resistor. Does this work? Would it make the light dimmer? I'm actually nervous about using 12v bulbs as I managed to melt a shell with one many years ago. I find the 1.5V bulbs stay cool and I reckon I can keep the resistors clear of the shell. (not always possible with bulbs - particularly with mars lights which I plan to light up.) As for LEDs - So far I am not impressed with them - they always seem to be either too blue or too yellow or (get this) I honestly think they are too bright. So what do you guys use? Anyone using 1.5v bulbs with resistors? Do you find the resistors get hot? have you tried higher watt resistors? what about 12v bulbs - do they get too hot? I'm going to get some assorted resistors of various wattages and ohm ratings and do some tests with a plan DC 12v power pack and some 1.5v bulbs.
I have started converting my DCC decoders with yellow LED's to white LED's, as it is a simple swap. I have solved the color/brightness issue to my satisfaction by using clear paint on the back of the headlight lens (orange clear paint from Tamiya), which tones down the brightness and removes some of the objectionable blue tint. I have less problem with blue because I model Conrail and the locos are blue anyway!!!
I have been using 3.0 volt bulbs instead of 14 volt, 12 volt or 1.5 volt bulbs. That way I split the heat problem between the bulb and the resistor. In my limited electrical knowledge, increasing the wattage rating of the resistor won't decrease the heat in the resistor. You are using the resistor to disapate electrical energy in the form of heat. The rating on the resistor in watts is just a measure of the amount of energy that the resistor can disapate without burning out. In most HO application a 1/2w resistor is fine. What you need to do is make sure the resistor is touching the frame and not the body shell so it can disapate the heat without melting the shell.
Hi there Rob, I model in HO, 40's era steam, and Lenz DCC. I use 1.5v, 14v, and LED's both in my rolling stock and on the layout. My headlights, except when factory equiped with LED's are 1.5 bulbs, as are my loco,tender, caboose marker lights and operating switch stands. Passenger cars are 14v, there's more room, and I don't have to use a dropping resistor. I use the 1.5's because of size, haven't found 12/14v bulbs small enough to fit inside the Tomar marker lights. When I first started putting in marker lights, I glued a resistor to the shell of a doodlebug, ncng is correct it will deform the plastic, as will a LED if placed too close to a thin shell. Now I use a piece of un-shrunk heat shrink tubing slipped over the resistor and then using Duco Stik-Takstick it where it will do the least harm, usually on the bottom of the tender. That stuff is great, I use it to hold wires, speakers and decoders where I want them. The neat part is the stuff stays flexable so if I have to rearrange things, I can. If you model diesels you should think about using fiber optic cable for ditch lights and number boards. I've not tried it myself, but hear lots of good things about it. LOL
<blockquote>quote:</font><hr>Originally posted by yankinoz: What do you guys reckon out there in DCC land? I have been using and like 1.5v bulbs in DC locos (with the classic diode constant brightness circuit) for headlights and ditch lights. Anyway I'm getting ready to get my toes wet with DCC and am hearing conflicting stories about 12v and 1.5v bulbs - namely the heat associated with dropping resistors. What sparked the debate in my head was Bill Darnaby's article in June MR - he uses 1.5v bulbs and says if the resistor gets too hot, substitute a higher wattage resistor. Does this work? Would it make the light dimmer? I'm actually nervous about using 12v bulbs as I managed to melt a shell with one many years ago. I find the 1.5V bulbs stay cool and I reckon I can keep the resistors clear of the shell. (not always possible with bulbs - particularly with mars lights which I plan to light up.) As for LEDs - So far I am not impressed with them - they always seem to be either too blue or too yellow or (get this) I honestly think they are too bright. So what do you guys use? Anyone using 1.5v bulbs with resistors? Do you find the resistors get hot? have you tried higher watt resistors? what about 12v bulbs - do they get too hot? I'm going to get some assorted resistors of various wattages and ohm ratings and do some tests with a plan DC 12v power pack and some 1.5v bulbs.<hr></blockquote> Rob, I've been looking into installation of a beacon light on an Atlas SD60. The smallest amber LED that I've been able to find so far is too big to be used with N-Scale. Although it only measures 3mm, when its measurement is converted to full scale, it's just over 18" in diameter. That's a few inches larger than the actual unit. Apart from this, I've read that the visual effect received through use of an LED as a beacon are not as good as those achieved through use of a light bulb. I've been considering use of the grain of rice bulbs, specifically the 1.5v units. I'm leaning this way because at 2.2mm, the bulb is closer to the actual scale size of a beacon. It also has a longer burn life, 10,000 hrs as compared to 2500 hrs for the 12v grain of wheat bulb. According to my calculations and considering use of a 12v source with 1.5v bulbs drawing 30ma, the voltage dropping resistor should be 1/2 watt (P=ExI, P=10.5x30ma, P=0.315 watts). Considering installation will be done in an N-Scale unit, there is plenty of free space in the SD60 to accommodate install of a resistor of this wattage. The wattage of a resistor relates to the amount of heat energy the unit can safely dissipate without burning up. Increasing or decreasing the wattage has no effect on the voltage drop across the resistor, thus the brightness of the bulb remains the same regardless of the wattage rating. What governs the lamps intensity is the resistors resistance. For the example given above, the resistance equates to 350 ohms. However since resistors aren't manufactured in this value, I would likely bump the resistance value up to 470 ohms. Using this value, the voltage at the bulb would be 1 volt while the current draw would be 20 ma's. Using a 1.5 v, 30 ma bulb in this configuration would likely result in a dimly lit bulb. Moving the resistance downward to the next available value of 330 ohms slightly increases the current within the circuit (31.5 ma’s). While making the bulb just slightly brighter than normal, the life of the bulb is likely to be shortened. With this information in mind, using a 1.5v bulb that draws 20 ma's would be a far better solution. While still using the same 470 ohm 1/2 watt resistor, the bulb would receive full voltage, thus full brightness and lamp life would be achieved. BTW: Thanks for the feedback on my layout. I’m still considering your suggestions and my options. Bob
<blockquote>quote:</font><hr>Originally posted by ncng: < SNIP > In my limited electrical knowledge, increasing the wattage rating of the resistor won't decrease the heat in the resistor. You are using the resistor to disapate electrical energy in the form of heat. The rating on the resistor in watts is just a measure of the amount of energy that the resistor can disapate without burning out. < SNIP > <hr></blockquote> For clarity; increasing the wattage rating of a resistor won't decrease the heat energy that's developed within the resistor. It will however offer a larger area for heat dissipation, thus the resistor will run cooler. In comparison, think of the size of the radiator installed with a four cylinder engine to that installed with an eight cylinder engine. There's much more heat to dissipate from the eight cylinder engine, thus the radiator will have to be larger in order to maintain a surface temperature similar to that of the four cylinder radiator. Bob [ 11 July 2001: Message edited by: original_black_bart ]</p>
<blockquote>quote:</font><hr>Originally posted by yankinoz: Crystal clear Bob! Thank You. How do you calculate the voltage drop?<hr></blockquote> In my first example I assumed the lamp would be supplied with its rated voltage, 1.5 volts. Using this information, the voltage drop across the resistor was calculated by subtracting the lamps voltage from the source voltage. The result was 10.5 volts being applied across the resistor (VR=VS-VL, VR =12v-1.5v, VR =10.5v). Keep in mind that current in any component of a series circuit will be the same as that of any other component. Given the lamp and resistor are in series, the current through the resistor is determined through knowing the lamp would draw 30ma at it's rated voltage. The current through the resistor would then also be 30 ma. Calculating the resistors resistance for this example is easy. This is done based on the information derived above and through the application of Ohms law. Using this data, a resistance of 350 ohms was calculated (R=E/I, R=10.5v/30ma, R=10.5v/0.030amps, R=350 ohms). Remember, resistors aren’t available with a value of 350 ohms, thus we’ll need to use either a 330 ohm or 470 ohm unit. Let’s assume the use of the 330 ohm unit. Doing so will help demonstrate why I elected to move to the 470 ohm unit with a 20 ma bulb. Prior to calculating the voltage across the resistor used in this example, we first need to know the current flow through the series circuit. Given the value of the 350 ohm resistor was changed to 330 Ohms, current in the circuit will also change. Since we lowered the resistance, the current will increase. With a source voltage of 12 volts and total series resistance of 380 ohms (the sum of the 330 ohm resistor and the 50 ohm lamp), the current in the new circuit is calculated by applying ohms law. In this case the amperage in the circuit would be 31.6 ma (I=E/R, I=12v/380ohms, I=31.6ma). Using this information the voltage across the 330 ohm resistor can be calculated (E=IxR, E=31.6ma x 330 ohms, E=10.4v). The result of the calculation is 10.4 volts. This is 0.1 volt less then the voltage that appears across the resistance of the 350 ohm resistor. It’s not a significant amount by itself, but in consideration of the 1.6 volts that are now being applied across the bulb (VL= VS - VR, VL=12v – 10.4v, VL=1.6v), the 10% tolerance level of the lamp voltage (VT=1.5v x 10%, VT =0.15 v) is close to being exceeded. This increase in voltage may act to reduce the lamps overall life. This is not a situation I’m willing to accept when affixing a lamp to an engines shell with adhesive. Hopefully you won’t find my ramblings confusing and will be able to apply the information to other series circuits. Bob
I've noticed on the thread lots of folks talking about grain of wheat and grain of rice bulbs. I use a lot of them in my layout. One thing you must be careful of is the amperage of the bulb. Minitronics sells grain of rice 1.5 volt bulbs and publishes that they have 30ma of current. I was playing around with a package of bulbs and found that the amperage varied between 30 and 45ma. you should check the amperage of each bulb, when they're that small quality control is difficult and will change the value of the resistor you want to use. Do some testing!!!
If space allows, there is no reason you couldn't use two resistors, in the case above, a 330 ohm and a 27 ohm to get 357, close to the 350 required. Gary
<blockquote>quote:</font><hr>Originally posted by Gary Pfeil: If space allows, there is no reason you couldn't use two resistors, in the case above, a 330 ohm and a 27 ohm to get 357, close to the 350 required. Gary<hr></blockquote> That's a good idea Gary. I'm playing with wiring a 1.5v bulb into each headlight and numberboard in series (all 15ma) - if I am correct - this will be 6v and still 15ma. so I won't need so big of a resistor. In early experiments they look pretty good (with a AA battery for power sitting on my workbench.) They aren't as bright as LEDs but like I said before, I find overly bright headlights distracting. And WELCOME to trainboard!
