Model Railroading > Resistors

Ok all you electronic geniuses out there, what resistor should I use with a 1.5 volts 15mA 1.2mm bulb for ditch lights on Proto SD60M.

You should use at least an 800 ohm or greater resistor. I use something like an 840 or 860 ohm resistor for ditchlights.

You should use a 680 Ohm 1/4 Watt or 1/2 Watt. The 800 Ohm series is too much. Why do I know this? I have tried it. The 680 Ohm is the correct resistor. I assume you are using DCC? If not, the lights will not be very bright unless you have the power up fairly high. In the case of DC power, you can get away with a slightly lower Ohm resisor (480 - 560).

The best thing to do is to experiment with it a little. If you use a minimum of a 480 you will not burn out the bulb. Just make sure that you don\'t have more than 16V on the track.

Hope this helps.
Rio Grande Fan

Yeah, you can use 680 ohm resistors on headlights that are wired in series. How do I know this, because thats what I use for my headlights. If you want the ditch lights to work on DCC, you need to use the 800+ ohm resistor. How do I know this, because me and a bunch of other guys at the club use these on our operating ditch lights. If you just want the ditch lights to light up and not flash, then yes, you can wire them in series and use the 680 ohm resistor.

WHat if I put one resistor per ditch light. How many Ohms per light?

> WHat if I put one resistor per ditch light. How many Ohms per
> light?

720-ohm, 1/4-watt.

See here to calculate Ohm\'s Law quickly: http://www.mostgraveconcern.com/jgl/engineering/ohm/index.html

(Remember, E in the equation is what the resistor drops, not the bulb...)

--Dan

ok here is a different question, sorry for getting off the subject, What Resistor would I use to take a 12 or 14 vold power pack, AC, and take the power down enoght so I could use a 1.5 and 15ma bulb so I could use it for a street light, or lighting up a car. Thanks.

Andrew

Depending on how bright you want the light to be. In the preceeding replys, you can see that the resistor value is going to be around 680 ohms or higher for each 1.5 volt bulb. A headlight on an engine would certainly be brighter than the headlights on a model car. You know the ballpark now and the resistors mentioned are available at Radio Shack in packets of 6. You can experiment yourself for the fine tweeking.

Ken, D&J Railroad, Stafford, VA

For DCC when wiring headlights and ditchlights, (does not matter) they have to be wired in parallel. They just don\'t light up when wired in series (tried it, they don\'t light). Each bulb gets its own resistor, and for a 1.5V 15MA bulb this resistor is 680 Ohms. This is the same if you want flashing ditchlights or solid ditchlights. It doesn\'t matter what light you are trying to light up, or what feature you are trying to use, the bulbs should be wired in parallel with their own 680 Ohm resistor.

I have hardwired over 200 decoders and have experimented with all types of bulbs and all types of resistors. This is what works, I can guarantee it for life!

Miniatronics Bulbs
1.5V 15ma 500 hour life 680 Ohm 1/4 or 1/2 Watt
1.5V 30ma 1000 hour life 390 Ohm 1/4 or 1/2 Watt

I can guarantee the above information will work every time with DCC! I own about 50 locomotives that have the 1.5V 30ma bulb and I followed this exact formula, and my bulbs are nice and bright, and look very realistic. I have yet to burn one out.

No matter what loco it is, I use these Miniatronics bulbs. I order them 70 bulbs at a time for my installations, and the people I install decoders for. I really like them, and most of all they work. I order my resistors from Circuit Specialists (http://www.web-tronics.com) in quantities of 1000 at a time for $3.

I have been doing these decoder installation for the last 3 years!

If you should have any furthur questions feel free to e-mail me!

Lee Ryan
AKA Rio Grande Fan
Denver, CO
lr_trains@yahoo.com