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Post by santafe49 on Oct 4, 2022 9:03:57 GMT -8
Hello all,
Trying to add Ditch lights to an Athearn BB GP50. I am using prewired 0402 WW in DW castings. I have the LED's set up in parallel. The decoder is a Soundtraxx MC2H104AT board.
Now comes the strange part. In checking to insure they work, i use my 3V coin test clips and the LEDs light up just fine. BUT, when i put a 1K resistor inline with the NEG side of the LED wiring, and use a 9v battery to check it i get nothing. Using my meter i get 999ohms across the resistor.
Yes i have checked the polarity of the connections to the LED's.
I have used a resistor calculator online to see if i need a different resistor. I will have the lights going to the FX5 tab on the board. I checked the output voltage of the FX5 tab and get 12.9V. Based on the voltage, voltage drop of 2.8v for the LED's and 40ma current, the calculator said a 202ohm resistor is required. I am hesitant to go that low as i don't want to smoke the LED's in the castings.
Any suggestions will be greatly appreciated.
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Post by edwardsutorik on Oct 4, 2022 11:40:57 GMT -8
Yes, better to smoke them outside the casting. So that's where I'd be doing my testing.
I found when I was trying to dim an LED that there was a point where, as I increased resistance, the light output just stopped. 1K doesn't seem that high, but....
Out on the bench, I'd try the 202, and see what happens. If they light, I'd probably try again with something like a 150. If they still light, that endorses using the 202.
Or so it seems to me.
Ed
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Post by NS4122 on Oct 4, 2022 15:25:09 GMT -8
If you're afraid of smoking the LEDs in the castings, I would go the other way. Start with a 750 ohm and or maybe a 680 Ohm before going as low as 202 ohms which might be too low.
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Post by edwardsutorik on Oct 4, 2022 16:55:51 GMT -8
Some clarification please:
Are these LED's only available inside the castings? Or can you get them loose?
Ed
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Post by Mark R. on Oct 4, 2022 19:45:57 GMT -8
Yes, 1000 ohms is way too high for a 9 volt supply test. For 9 volts and the two leds in parallel, the resistor value should be between 150 and 330 ohms. 150 will run them at their peak intensity (which isn't really necessary). 330 ohms will still be plenty bright but with less stress on the LEDs.
For 12.9 volts, the range should be 240 to 480 with the same range reasons as above.
Keep in mind that if one LED goes bad for whatever reason, the remaining LED will get the full brunt of current. It will survive with the higher resistor, but not likely with the lower value in the range.
Mark.
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Post by santafe49 on Oct 5, 2022 12:01:37 GMT -8
Well, i did the 480 ohm and it worked just fine. A tad dimmer but it looks fine. I don't have a 330 so i will leave it as is.
Thanks to those who provided guidance.
As to the mounting. They are Details West DL-229 Ditch Light castings with 0402 LEDs mounted in the rear facing forward. I attach them with canopy glue. I then put a dab of black liquid tape on the back to block any light leakage out the back. The assembly is then attached under the anti climber with CA.
I know these are for GE locos but they were what i had and so i used them.
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Post by kentuckysouthernrwy on Oct 7, 2022 6:57:43 GMT -8
A great tool for making such tests is a relatively inexpensive resistance substitute box as seen here…Elenco Resistor Substitution Box - K37 google to see unit. Elenco Resistor Substitution Box - K37 (Kit Form, Soldering Required) a.co/d/06QeO8H Several in my area have used them to find what they need.. It is a kit with some very basic soldering needed…our area all thing electronic guru did all that for mine… Link tested, worked for me…no connection with the company, Yada, yada…  |
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Post by edwardsutorik on Oct 7, 2022 10:40:51 GMT -8
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Post by santafe49 on Oct 7, 2022 11:46:00 GMT -8
Thanks for the links. I just might have to invest in one. Would surely make selections easier.
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Post by kentuckysouthernrwy on Oct 7, 2022 13:33:06 GMT -8
Mine was assembled, too. Our local group ordered some that our soldering guru put together, I think he gets a buzz from solder resin…  |
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