I will install a TCS T1 DCC Decoder in a Proto 1000 F3A which is known to be equipped with one 3v bulb. Which resistor should I use? How can I calculate the right value for the decoder?
Guy
Modeling CNR in the 50's
Guy,
If you're going to do that you might also want to switch out the incandescent for an LED. Either one would be 3V and a 1K resistor would work with either one.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Need to know the supplied voltage and the milli-amp rating of the bulb in order to calculate the resistance.
The supplied voltage from your decoder will be 1.4 volts less than your track voltage. In order to figure the ma rating of the bulb (which I assume you don't) - connect the bulb to a 3 volt power supply (power pack set to 3 volts will work) and connect your meter in series with the bulb, set to read milli-amps. This will tell you the current draw of the bulb. I would guess it to be about 30ma.
With these figures in hand, divide the voltage (your supply voltage - the bulb voltage) by the current to get the resistance. The formula is V / I = R.
Say for example your supply voltage is 12 volts and the bulb's current draw is 30ma. the formula would be (12-3=9) divided by 0.030 = 300 ohms resistance.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Mark:
If I can ask a question based on my admittedly limited knowledge of electronics, wouldn't the OP be better off using a higher value resistor to extend the life of the bulb?
Guy:
I will second Tom's suggestion of replacing the bulb with an LED. A 3mm warm white LED will fit quite nicely where the bulb sits now. The LED will last for thousands of hours whereas the bulb, even with the voltage reduced, will fail sooner or later. If you choose to use an LED, a 1000 ohm 1/4 watt resistor will work fine. You can go down to a 447 ohm resistor to maximize the brightness but there really isn't much of a difference.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critterI will second Tom's suggestion of replacing the bulb with an LED.
another vote for LED's here, too!
I have several examples of my early Proto decoder conversions where the stock lamp generated so much heat that some of the plastic softened to the point of distorting the shell.
All you have to do is park the engine and forget to extinguish the headlight and the heat will build up and melt the plastig.
Just tonight I had to chuckle when I ran a few of my early Proto FA-1s that hadn't been run for some time, and noticed on one unit that the windshield had melted and distorted beyond recognition! I must have already swapped the bulb for an LED but didn't notice the melted windshield until tonight.
TCS has a T1 that is geared for LEDs.
https://www.tcsdcc.com/Customer_Content/Literature/Decoders/HO_Scale/T-Series/T1-LED.pdf
Many of the newer decoders have options that make LEDs look and act more like incandescent lamps by ramping up or down the brightness instead of instant on/off. Many have dimmable headlight functions as well.
Once you get the hang of mounting the LED and finding the right ones for the job you'll never go back to incandescents. Just my 2¢
Good Luck, Ed
gmpullman TCS has a T1 that is geared for LEDs. https://www.tcsdcc.com/Customer_Content/Literature/Decoders/HO_Scale/T-Series/T1-LED.pdf
TCS has a T1 that is geared for LEDs. https://www.tcsdcc.com/Customer_Content/Literature/Decoders/HO_Scale/T-Series/T1-LED.pdf
Lost DCC newbie here
The OP wants to use the T1The T-1 says it has a resistor for LED's and bulbs. I do not see what size resistor mentioned in their literature. Everyone, as I read the answers and maybe I need another cup of coffee, says he still needs another resistor for an LED.
Doesn't the T1 resistor count for anything?
Henry
COB Potomac & Northern
Shenandoah Valley
Thank you all for the responses. I did a few conversions from DC to DCC lately and every time I replaced the bulb by a Led as frequently suggested in this forum. Every time but once. It was with the same model, a Proto 1000 F3A. I just couldn't figure out how to remove the bulb from the end of the tube it is fixed in.
On thAT model I didn't had to figure the value of the resistor as it was DCC ready and I could use the TCS LL8 as suggested by TCS.
There's a T1-LED and a T-1. The T1-LED has resistors and no additional ones should be needed (unless the LED is too bright). The T-1 does not have resistors and you need to add your own. Depends on the price difference between the decoders - resistors are about 2-3 cents each in quantity.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
hon30critter Mark: If I can ask a question based on my admittedly limited knowledge of electronics, wouldn't the OP be better off using a higher value resistor to extend the life of the bulb? Guy: I will second Tom's suggestion of replacing the bulb with an LED. A 3mm warm white LED will fit quite nicely where the bulb sits now. The LED will last for thousands of hours whereas the bulb, even with the voltage reduced, will fail sooner or later. If you choose to use an LED, a 1000 ohm 1/4 watt resistor will work fine. You can go down to a 447 ohm resistor to maximize the brightness but there really isn't much of a difference. Dave
You have to approach the calculation different with light bulbs as opposed to LEDs. LEDs have a fixed voltage drop, and the changing resistor values alters the current flow, which alters the brightness of the LED. So if you want a dimmer LED, you just use bigegr and bigger resistors until you reach a point where so little current flows that the LED won't light.
With a light bulb, the current is constant (within reason - there's also an inrush current with lamps since the cold filament has a lower resistance than a hot filament - which is why it often is recommended to use a small value resistor even if the bulbs are rated for 14 volts, to reduce the inrush and keep it from blowing the decoder function line because of overcurrent) and you vary the voltage to adjust the brightness. So where with an LED you always take the source voltage - the LED drop and divide by the resistor to figure out current, or divide b desired current to figure the desired resistor, with an incandescent bulb you know the current, and you know the resistor, so the calculation gives you voltage drop across the resistor - say 50ma bulb, and a 1K resistor, that's 50 volts, which means the bulb cannot light up on 12 volts - the resistor drops all of it. The higher the current of the bulb, the smaller the resistor needed, in resistance value. But there is also the wattage. To get a 10V drop on a 50ma current, the resistor value would be 200 ohms. But the power dissipated by the resistor would be I^2*R, .5 watts. You would need a 1 watt rated resistor (the next step up from a half watt one - you don't ever run components right at the max value if you want them to last). It would get rather warm, though the 3V bulb running on 2V would have a nice soft glow and probably not get too hot. You're just transferring the heat from one component to another. Same calculation with an LED, using a 1K resisotr and let's say it comes out to 10ma (It's more like 9 but 10 makes the math easier - it's Monday morning). Then you get .1 watt - so a 1/8 watt resistor is ok and a 1/4 watt is plenty sufficient. That's why higher current bulbs like those in the Proto locos are a double whammy - the light bulb itself gets warm, and so does the dropping resistor you need to keep the bulb from burning out. The cooler you run the bulb, the warmer the resistor gets, and vice versa - the power in has to equal power out. Now instead of melting the shell around the headlight it melts the shell in the middle where the resistor sits...LEDs are definitely the way to go.
Unfiltered output is typically 12V
V = I R
12 = IR1 + IR2
12 = I (R1 + R2)
Equation 2:
3 = .052 R1
R1 = 58 OhmsBack to equation 1:
12 = .052 (58 + R2)12 = 3.016 + .052 R2
12 - 3.016 = .052R2
8.984 = .052 R2
173 Ohms = R2
You'll need a good 1/2 watt resistor for that btw. Personally I would start in the low 200-220 Ohms to prolong bulb life.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Thank you all for all the information.
When I initiated that thread, I was out of town. Upon arrival a few hours ago, I went to the train room and had a better look at the engine. With great surprise, the bulb fell easily out of the tube it was inserted in. I should have had a better look before but, having not been able to move the bulb in my first F3A, I didn't even gave a try on this one.
My problem is then solved. I will make a hardwire "à la Randy". I will remove the original pc board and solder the wires directly to the harness of the T1 decoder. I will use a Led as suggested by the majority and use a 1kHoms resistor on the white wire.
After that, I will reopen my first F3A and do the same even if I have to destroy the bulb to remove it from the tube it is inserted in.
Thank you again to everyone for the help. I greatly appreciate it.
Thanks Randy.