I know next to nothing about wiring. I have, however, run a bus line under my benchwork--a separate bus line from a simple power pack separate from my DCC Zephyr. Now-- accessories I have to install, like street lights and building lights mostly have two black wires. How do I know which of these wires to attach to which of the two bus line strands? eagle37
It doesn't matter if it's an incandescent bulb/lamp - either wire to either bus, assuming the lamp and power supply voltages are the same. If you have a different lamp voltage to that of the power supply you will need to use dropping resistor/s to limit the voltage to the lamps. When it involves specialised circuitry, LED's, or the above, then voltage and (DC) polarity is important and I would expect these items to be marked accordingly.
Eagle: If you are powering lamps only and no LEDs or fancy electronic circuitry ( diodes, transistors, capacitors, oh my!), it won't matter which you hook up to either wire. If you are using smaller lamps (such as 1.5 volt grain of wheat lamps), then you'll want to include a resister in the circuit to keep from frying a 1.5 volt lamp with your 12 volt power supply. Radio Shack sells dozens of sizes of resistors for about 20 cents a piece...5 for a buck. When I have some light bulb project to do, I just buy a variety of resistors and light bulbs and experiment with what resistor value I need to put into the circuit to get the level of brightness I want or the amount of protection I need to light the bulb without frying it. Perhaps someone can offer some general guidelines (or links to sites that offer them)for us to follow in selecting proper resistor values so we can light 2 or three 1.5 to 3 volt lamps with our 12 volt supplies without our lamps going out in a blaze of pyrotechnics. There are formulas out there for calculating appropriate resistor values...could someone post a simple description and a couple examples for TBers willing to do some basic calculating for basic projects, like lighting our structures and street lights? At the risk of moving a little away from Eagle's original question, I'd like to add a different but related question: I recently ran into some issues when I tried to power too many Tortoises and indicator lamps with a 12 volt DC wallwart that was only 300 milliamps strong. Once I got the Radio Shack 1500 milliamp (1.5 Amp) power adaptor, I didn't have any problems. 1. Could someone please offer a "Rule of Thumb" for figuring out how many light bulbs of what particular size can be lit with a wallwart or power adaptor of x milliamps (and throw in 2 or 3 examples to help us understand the Rule's application a little better)? ---If I know the size of my power source, how do I figure out how many lamps I'll be able to light? I suspect the Rule of Thumb can go the other way too: Besides waiting until we see the smoke come out, smell hot circuitry, or burn our fingers on an overworked power pack, adaptor, or wallwart (all signs that show up after the fact instead of before)...how can we figure out ahead of time how many milliamps (or amps) we will need to safely put lights in our buildings? ---If I know the number and size of the lamps to be lit, how do I figure out how big a power source I'll need?
To answer Dave's question and give the general rule of thumb is watts = voltage x amps. If you have the lamp sizes (wattage and voltage) then you can use the above formula to ascertain the current draw and hence the capacity of the power supply, power supplies, needed. For example, if you have a 12V 0.5W lamp on a 12V supply it should draw 0.5/12 = 0.041666A (41.666mA). So a 500mA 12V supply should power 500/41.666 = 12 lamps, a 800mA supply should supply 19 (800/41.666 = 19.2 rounded down), and so forth. Note - this assumes no losses in the wiring and working to the power supply's nominal output.
The accessories you buy... streetlamps, etc. Should have the voltage rating on the package. If you're putting lights inside of buildings you will probably buy generic small lights, then you have to pay attention. Get 15 volt lamps and you'll be fine. If you get LED's then you have to worry about which wire goes to + and which goes to -
Is the + or - for LEDs the only problem? Do they need resistors, too? I have a module that simulates an arc welding flash. Can this be installed using the same principle as a bulb? If you know the voltage and the watts, just compute the resistance needed for the resistor for the module? Does this same principle apply if you are using a power pack with an "accessories" terminal? I like to use these as they are very inexpensive and easy easy to find. What is a wallwart? Thanks from the electronically challenged.
Yes, LEDs need a resistor. They only drop about 3 volts, so if you're using a 15v power pack you need a resistor in the range of 470 ohm - 560 ohm to drop the rest of the voltage or the resulting current will burn out the LED. I would think that the arc welding flash module would work on the same principle as a bulb, but I'd like to read the directions before passing final judgement. An "accessories" terminal usually is 16 volts alternating current (16vac) where the power pack's terminals that connect to the rails is 15 volts direct current (15vdc). You should check to see if your accessories require DC or AC current. The AC accessories terminal is also a constant voltage level. Using lamps on the DC side allows you to dim them with the throttle. This can be a nice effect, but usually requires a separate power pack as you don't want your lights varying with your throttle speed. wallwart is a misspelling of Wallmart or a new kind of growth on the skin that I haven't heard of before.
To say you know nothing about wiring is almost like saying you know nothing about driving. To get from home (the power supply) to work (the load) and back you must first drive on neighborhood streets (small gauge wire), but staying on your own side of the road (one wire of your bus), then on the expressway (large gauge wire) until you get to the office and do your work (light the bulb, run the motor). Exhausted, what’s left of you then heads back home over the same route, but in the opposite lane (the other wire of the bus). You may encounter one-way streets (diodes, transistors and other “oh my” things) that cause you to go in a slightly different direction, or you may need an extra push (an amplifier or booster) up that hill (high resistance), and once in a while a drawbridge (electrical switch) may be open (turned off), but you’ll make it back home (the power supply) eventually unless you cross the yellow line (short circuit) and get into an accident (blown fuse or circuit breaker). In that case you will need a tow truck to clear the road (remove the short) so traffic can get moving again (replace the fuse or reset the breaker) and get yourself to the hospital (THIS FORUM!!) to get it all straightened out. So buckle up and enjoy the ride! :tb-wink:
If you are powering street lights etc from the DCC track I doubt there is a need to worry about which way around the LEDs go as the track supply is a form of AC. I would be wary of using too many dropping resistors to, for example, supply 1.5v lamps from the DCC track voltage of 15V or so as in that example the resistor would consume almost ten times the power used by the bulb. I would use higher voltage globes or wire ten lights in series.
Okay, here's what little I've been able to learn: R=[V(in)-V(bulb)]/I(bulb) V(in) is your power source. For a power pack, it's 12 VDC. V(bulb) is the voltage drop across the bulb, and I(bulb) is the desired current in amps. So if you have a little bulb that is 1.5 V and 15 mA (15 mA=.015 A), you subtract 1.5 from 12, then divide the result by .015. The resistor should therefore be at least 700 ohms. Always use a resistor that is more than that value, which in this case is a 820 ohms resistor (gray, red, and brown). (12-1.5)/.015=700 If you wire some bulbs in series, they are more protected, so you just divide this value by the number of bulbs to find a smaller resistor. So if 700 ohms, you now need a single 70 ohm resistor for the set of 10 bulbs. The resistor can be placed anywhere in the circuit. Location doesn't matter. As far as LED's, go, I think you can use the resistor value that you've calculated, as they aren't as sensitive. Each color of LED has a different voltage. Use Google to look for "LED resistor calculator," and you'll find any number of websites that will do this for you. Current limiting Resistor calculator for leds is a nice one. It will probably correct any errors I've made in trying to help. :tb-embarrassed: A short beginner's page: LED Circuitry tutorial: how to hook up LEDs. Cristi
Flash: Wallwarts are those power converters or transformers that plug into the wall outlets and convert 110 or 120 volt household AC down to 12v AC or DC. (Actually, depending of what it is used for, the conversion could be down to as little as 3 or 4 volts for charging cell phones, Dust Busters, telephones, pencil sharpeners...the list goes on and on and on... and might only be down to 22 volts.) They get their nickname from their appearance: little bumps on the wall, usually no larger than your fist, and they will often be black or brown (although I currently have several white, cream, or gray ones.)
