Has anyone ever used a decoder's motor outputs for lighting a passenger car or caboose? I was thinking of trying this since it would allow me to dim the lighting. I will be using LED strips so I would assume I would have to make sure I never use reverse unless I put in some electronic protection against reversing polarity.
I've never tried using the motor's output, but it is entirely possible. A small diode bridge rectifier would take care of the polarity reversal problem. Connect the decoder's motor outputs to the inputs of the bridge rectifier, and the outputs to the LEDs. The input polarity would then make no difference at all.
I'm thinking it should work, sicne the motor output is pulse width modulation, which is pretty much the only way to dim an LED. If there's only a limited range, you could implement a speed table to get rid of the low end where it's too low to even light up, and the upper end where once you hit a certain speed step, it never gets any brighter.
Hmm, some decoder testers have LEDs to indicate forward and reverse - do they change brightness, or are they always on for the respective direction? That would prove out if this will work or not.
By "not work" it would just turn the LEDs on and off, no dimming - it's not going to blow up the LEDs or the decoder.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Yes you can. I built my first decoder tester using a green/red LED with a 1k resistor. Worked very well. I had found a circuit online to build a decoder tester.
Some colored LED's with 1k resistors for different functions. Actually quite simple.
Using an old can motor with a flywheel was better though.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Should work fine. If the decoder has BEMF compensation, make sure it is turned off.
Although the motor voltage is PWM, that is, positive or negative 12 to 14 volt pulses of varying width, depending on the speed, the LED or even a light bulb will see it as DC voltage.
I would make sure you bench-test your setup before you actually install it.
I'm just wondering how much "dimming" you're going to get. Even the "dimmable" 115V LEDs I'm using around the house only get down to about 40% light output and some hardly have any dimmable range at all. You pay extra for the dimmable option on household LEDs.
You might find that your dimmable range isn't worth the bother of using a decoder. Then again maybe if you experiment a bit it will work to your liking?
Just sayin'
Ed
Thanks for the replies. I'm going to try it out this weekend and I'll post the results.
I first intended to use a Digitrax TL1 for just an on/off function but then saw that a DZ123 is only a few dollars more and has outputs I could use for other lights if I needed.
As far a diming, I found a few posts on the web about using different value resisters to adjust the lighting so my thinking was why not just use the motor output?
Thanks again.
Worked pretty good. The LEDs come on a bit before 1 on a Digitrax Zephyr Extra throttle and full brightness is a bit before 2. I ordered some small bridge rectifiers so I won't have to worry about polarity being reversed. Here's the results:
Guess I can't post photos? I can drag photos to the edit window but they do not appear when I post.
You have to host the photos somewhere - your own website, or a photo site like photobucket or imgur