About Lighting, Light bulb selection, Resistor Selection, 1.5 volt bulbs, and A6X decoder connections





Question: I have a Bachmann Spectrum HO scale 3-truck Shay that I am trying to chip for a customer. Now, from my previous experience, and by lifting the board in the engine to see underneath, I am fairly certain that the (off the TCS-150W chip) orange lead goes to slot "1", and the grey lead to slot "5", then the power pick-up and return leads - black & red - go to slots "4" and "8", respectively, from what I saw under the board. Usually the light return leads, blue, go into slot "7", while the forward light, white, is slot "6" and the rear light, yellow, is in slot "2"! Just so we have the same frame of reference, if you are looking at the Shay tender from the rear, the "8" slot would be on the top-left corner. My problem is the DP-150W has ten leads, rather than seven! What do I do with the other three? Answer: This link is to our harness shop. There is a picture of the NMRA plug identifying the colors and pin numbers. http://www.tcsdcc.com/harnesses.html You can enlarge it by clicking on the enlarge button and print it out for reference. It should be helpful. Regarding the extra wires, they are extra function leads for lighting. You do not need them if you are not adding any additional lights. The green, violet and brown wires are functions one, two and three. Remember the TH150W is a five function decoder and you will only need two functions for the Shay installation for the front and rear lights. Question: On other manufactures decoders, there are strict warnings about replacing lamps pulling more than 30 ma and any 1.5 to 3 volt lamps that will not operate on the 15 V track power used in DCC. What do you recommend? Answer: There is no problem with TCS decoders driving 1.5v lamps, 3v lamps, or LEDs. The ratings on the functions are 150ma which you can use to easily power 30ma bulbs or LEDs which typically draw around 20ma with a 680-1000 ohm current limit resistor. Question: I have a T4X decoder and want to install dual headlight LEDs in parallel rather than in series. I intend to use a separate 1/4 watt resistor for each LED. The LEDs are 0603 and are 20ma at 3v forward current.
Should I use the single LED value for each resistor? Is their a potential problem with two LEDs in parallel putting too much load on the lighting circuit?
Answer: There is no problem in using two LEDs in parallel on the same function. Each function is rated to 150ma, with two LEDs drawing 20ma each it is still not being taxed to its maximum capacity. It is correct to use one current resistor for each LED. Each LED draws around 20ma with a 680 to 1K current limit resistor in series with the LED. Question: Hello. I just purchased the A6X for my Athearn Genesis SD75I. I want to use a total of six 1.5v light bulbs (2 for the front, 2 for the rear, and 2 for the ditch lights). What I am not sure of is if all the power supply tabs can be used can be used for this or not. My impression is that if you want all 6 tabs in 1.5v, the lead wire for each has to be soldered onto the 1.5v 120mA Power supply pad, and then to the proper solder pad. Answer: When soldering 1.5v bulbs onto to the A6X decoder you must only solder their leads to the 1.5v pad. A 1.5v bulb soldered on the 12v pad will lead to immediate burning out of the bulb. When attaching 1.5v bulbs to the board, one of the leads from each bulb must be attach to the 1.5v pad and the other lead must attach to a normal function pad. Question: I am about to install several A1 decoders in some Athearn Genesis SD70Ms and would like to know what size of resistor you would recommend for bulbs rated at 1.5v 15ma, as these are not mentioned in your chart, and when you say (2) 30ma Bulbs in series am I right in thinking that you can use just 1 resistor rated at between 270-330 ohms for the 2 bulbs on 14v track? Or would it be safer to use 1 resistor per bulb. Answer:
Please use the A6X decoder now available. It has a 1.5 volt regulated power supply on the decoder that eliminates the need for dropping resistors. If you have a A1 or A4X decoder that you want to use instead then the following information will help. I recommend testing each bulb with a resistor before installation. Try a 820-ohm 1/4-watt resistor to start. I have found that each of these little bulbs can vary in their actual rating as much as 15%. Also, a 5% resistor can be off 5%. Now you can be off for a total of 20% which is significant enough to either shorten the life of the bulb or the bulb is not sufficiently bright enough. If the 820 seems correct by judging the brightness of the bulb or by measuring the actual current with a amp meter then use the 820. If the bulb is too dim then decrease from 820 ohms to 750 ohms and test again. If the bulb is too bright or the millamps are over 15 then try a 910 or 1k resistor. All the resistors mentioned here are "common values" that typically can be found it Radio Shack or any electronics distributor catalog. Many times the 910-ohm resistor works out well. When using to in series you are right in using one resistor of 270 to 510 ohms in value. Question: I am having problems getting any lights to work off of ANY of your decoders. The problems stems from not knowing what the output voltages are off of the various "tabs" or wires off of the decoders. The track voltage is 18 volts (From a CVP Products EasyDCC system). The decoder runs great, its just my lack of knowledge of what is the problem. What dropping resistor is needed for 1.5 volt bulbs? Does it go on the White Tab/wire or the Blue Tab/wire.Most of these are in Athearn Locomotives, including an SD70M, 3 CF7's, and a couple of GP 38's. I have tried isolating the normal old Athearn light, as well as putting resistors in the circuit. Since I do not know the exact output voltages, I've tried several different resistor values. None of your literature gives the output voltages, so I do not know what to try next. Answer: The voltage on the blue wire is 1 volt less then the power on the track. If your system is putting out 18 volts, the voltage on the blue wire or tab will be 17 volts. I believe the Easy DCC has an adjustment to set the track voltage. I highly recommend you set the track voltage to 13 volts. There is no need to go any higher then that. If the track voltage is at 18 volts there is possibility for potential problems. The decoders are designed to operate between 10 to 14 volts track power. The best way to measure the track voltage is to connect a volt meter set to measure DC volts between the blue wire and the white wire of a decoder. With the meter hooked up, turn on the headlight (function zero). You will then get an accurate reading. Adjust the track voltage to obtain 12 volts between the blue and white wires. Do no try to read track volts directly with a digital meter. You will not get an accurate reading. This is because the track voltage is AC voltage at 10khz frequency. Most meters are not designed to accurately read AC voltage with frequencies above 1khz. They will typically give you a reading less then actual voltage! This is true of even good meters (Flukes, Beckmans etc.) By measuring DC volts between the blue and white wires of the decoder with the button zero (function zero) on you are sure to get a accurate reading. Regarding connection: The blue wire or tab is + 12volts DC. It needs to be connected to one side of every bulb to supply power to the bulb. The other side of the bulb needs to be connected to a function wire. White, yellow, violet, brown, green, pink, are function wires. Function wires supply the ground or negative side of dc power to the bulb. When using a 1.5 volt bulb you are correct to place a dropping resistor in series with the bulb. Each bulb needs its own resistor. That is to say if you are using four 1.5 volt bulbs you will need four resistors. Place the resistor in series with the bulb on the ground side. That is the white wire , yellow wire...etc. The value of the resistor depends on the rated milli amps of the bulb. If the rating is 12ma to 15ma use a 680 to 820 ohm resistor. If the rating is 20ma use a 470 to 550 ohm resistor. If the rating is 30ma use a 350 to 420 ohm resistor. Use ¼ watt power rating resistors. Question: I have a Replica British Rail class 45 diesel and two Lima HST power cars which currently have 12V dc directional lighting fitted. Both have diodes to achieve this. Can you tell me what the output rating of the M1 for lighting is please ? Can I connect the existing miniature light bulbs with their diodes to the M1 or do I need to replace them with LED's and a resistor and if so, could you please recommend the appropriate components and ratings ? Answer: The current rating is 100ma (.1amp) for the lighting functions. The M1 will be able to operate the bulbs supplied with the loco. No need to change to LED'S. If you did choose to go with LED'S you would need a 1K resistor 1/4 watt to limit the current to the LED. Question: After reading your instructions and blowing out light bulbs in my Atlas Classic RS1 I am writing to find out just what the voltage (nominal) at the ends of the decoder. I now have 14v, 30ma lamps in and they are dim when set for 00 in CV49/50. This also the first of your decoders and I like the operation very much. I also know about the 1.5v pad and may use it in the future for LED hook-up if the is what is to be used. Otherwise I can use the "normal" light contact if you will advise as to the resistor required (general Ohm-age). I can detail the requirement if necessary. The system in use used 14.3v on the track. Answer: The blue wire puts out .5 volts less then what your track power is. Since your track voltage is 14.3volts the blue wire will be about 13.8 to 14.0 Volts. It is measured in reference to a function wire that is turned on. The function wire (white ,yellow, green etc.) provides the ground. Therefore it must be turned on to get a voltage reading between the blue and a function wire. If you want to use low voltage bulbs you need to use "Ohms Law" to calculate the resistance value needed. Resistance = voltage/ current. If you have 14 volts at the blue wire and you want to use 1.5 volt bulb you must drop the difference across a resistor. 14volts - 1.5volts=12.5volts. 12.5volts is needed to be dropped across the resistor. If the bulbs are rated at 15ma then, Resistance = 12.5volts/.015ma =833ohms. If you want to use LEDs you need to use the 12volt supply with current limit resistance in series with the led. There is no need to use Ohms Law in determining this. Typical resistance values are from 470 ohm to 1k ohm. The lower resistance value will give brighter LED. However 1K is still plenty bright when using high output LEDS such as the Golden White LEDS that we supply.

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