Decoders and GOW bulbs


meanjean

meanjean

Member
The decoder I bought says this.

Function output ratings: Due to the high in-rush current of incandescent grain-of-wheattype bulbs (about 10 times their normal operating current) function outputs are rated at40mA each if used with incandescent bulbs. We recommend the Miniatronics part number mentioned above. If you wish to use 50-100mA rated lamps we recommend a22 ohm 1/4 Watt series resistor in function leads with each bulb (this will also greatly extend bulb life).

I have bulbs that are 30mA, do I need a resistor since I am using bulbs that require 10 less mA then what the outpus are rated for? I would think if I was using smaller mA bulbs I would need to use them? They make it sound if you use larger bulbs you need resistors?

Thoughts
 
Chad, I'm no electrical expert, but the concept of an "in-rush of current" into a resistance type device like a bulb makes no sense to me. You get a big jump in current requirements for starting a capacitance device like a motor but not a bulb. There is an almost instantaneous increase in voltage to heat the filament but that shouldn't be an issue in terms of limiting current or voltage. Assuming the 30mA bulb has exactly the same voltage as the output from the decoder, you shouldn't need a resistor. You might want a reistor to drop the voltage by maybe 20% so the bulb does last longer without a noticeable decrease in brightness but you don't need a resistor to run the bulb.
 
The bulbs I have are Mitey Lites 1.4mm 1.5 volt, 30 ma.
I will have to look and see how many volts the decoder is rated for.

I never thought in a hundred years model railroading would ever be this high tech and complicated!!
Who knew?
 
"in-rush of current"
Click to expand...
All this is , is the surge current when turned on. While the lamp filament is cold, the resistance of the filament is low (less opposition to the current flow) as the filament heats the resistance increases and the current then decreases to it's nominal value.
Or something like that :D

Cheers
Willis
 
I think you need a resistor just to drop the voltage so the bulbs don't blow up. I've used 30mA bulbs without hurting the decoder. To calculate the value:

(Voltage from decoder - Voltage of bulb)/ Current of bulb = resistance

Example:
(13.2V-1.5V)/.03A=390ohm
 
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Chad, unless the output at the decoder is 1.5 volts, you'll need a resistor to drop the voltage. The current won't be an issue but the voltage will since most decoders put out 12-16 volts for lights and you will immediately smoke your 1.5 volt bulb. There are some decoders that either put out 1.5 volts for lights or give you the option of 12 volts or 1.5 volts by cutting a circuit trace.

Willis, that "in-rush" of current to a light bulb should occur in micro seconds since the bulb filaments reaches nominal temperature in time too short to matter in terms of calculating resistors. Now, if the bulb is operating at or near the maximum rated voltage, you will burn out the filament faster and the starting voltage does contribute to filament destruction. Thus, it's a good idea to drop the voltage 20% or so since the bulb will look about the same in terms of brightness but it will last almost forever.
 
These decoders and lights are kicking my butt.
I bought a DA-SR and put it in the Proto 2000 SD9. I cut the traces for output 1 2 and 3. I hooked everything up as directed with 1.5 volt GOW bulbs. Tested on a DC track as suggested and I get no lights? Nothing. The bulbs are brand new out of the pack. I tested continuity of the bulbs on a volt meter and its there. I then put it on DCC and still no lights. Turned them on and off with the throttle thinking that was it, nope. I then put back on the factory 12 volt light and it doesnt work. A volt meter showed 14 volts on the rear light output but 0 on the front. Did I not cut the trace deep enough? How far do you have to cut it to cut the link? This is the 2nd decoder I am having a problem getting these 1.5 volt lights to work. The loco runs on DC and DCC no problems so I know that part of the decoder is working.

Oh whats the diffrence between a MARS light and Gyralight? I have an SP SD9 so I dont know which one I need.
 
This really puzzles me.
With the train on the DCC track the function outputs have 15 volts as per the volt meter. So I must not have cut the notches deep enough to engage the built in resistor. So I used a 470k resistor and that brought the voltage down to 4 volts but the lights still dont come on!. The function for the mars light is working also varying the volts from 9-15volts. The decoder is working but why dont the lights work? I tested again the lights and there is resistance between the leads. Somebody help me here!!!:confused::confused:

Lets see 4 volts going to a 1.5 volt bulb should produce some kind of light even if it burns out quickly wich its not doing!
 
Well, if the outputs still show 15 volts, you haven't cut the U shaped link completely through....or, you have a bad decoder. I'd call NCE at this point and walk through what you've done so far. They may be able to quickly determine that the decoder is bad or you're missing a step somewhere. Also, for an SP SD9, you'd want a Mars light. From a modelers perspective, the difference is not really very great. The Gryralite has a back and forth then up and down motion while the Mars has a figure 8 pattern. It's actually pretty hard to tell what's in use on a model.
 
There has to be something wrong with the decoder. I can put the light leads on the rails and it lights up with a resistor. I still show 15 volts on the the decoder outputs. I drilled completly through the board so I know the U link is removed. This is odd and frusterating. I will have to call the manufacturer on monday I guess?
 
After talking with NCE the decoder wont support 1.5 volt gow bulbs if I cut the U straps. I have to use LEDs. Thats ok. I guess by looking around 3mm leds fit the holes the factory headlights came in. Is this true? How well do the fit? Who sells LEDS cheap? DO you get what you pay for? $1.50 each adds up if your changing 4 to 6 a loco.

Thanks
Chad
 
You know, I was reading NCE docs for that decoder and it said to cut the U link to use with LED's. I guess the current must be limited to such a low level that an incandescent bulb won't light, although this doesn't quite make electrical sense to me. At any rate. you can get some excellent deals on LEDS's on e-bay. The seller at http://www.quickar.com/discrete.php?session=fb2LX4B0&sort=style&clr=white also sells on e-bay and has a good selection and good prices. 3mm LED's should fit the headlight holes fine.
 
Good news. The lights now work. I had to get LEDS and they work great. Bad new is the 3mm dont fit the factory hole. Some modification to the original lens seems to work.
 
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