I have a Soundtraxx Sound decoder I would like to test outside of the loco. Would I have to load the motor leads on the decoder with a resistor to get it to respond to my throttle? If so what would be a good resistor value?
I guess I should have said I know the motor functions work I will be cking the sound functions.
Thank you
I used a 100 ohm, 1/2 watt resistor when no motor was available. I finally made a simple decoder tester with a couple LED's and resistors for lights and a can motor out of an old CD burner from a cast off PC. I put a flywheel on the motor shaft to get an idea of the decoder response.
I recently had a loco with a small motor/light decoder in the engine. I found an old SoundTraxx LC sound decoder and it was easy to put it in the tender with a speaker. I put a resistor on the motor leads.
I did not want to pull the engine apart and remove the decoder in it. I only needed two leads to go between the engine and tender.
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.
I don't know what value resistor to use, but I would certainly use one. I tried bench testing a decoder, by carefully attaching wires to the power pickup tabs only. The decoder came on with engine sounds, and the horn blew, but when I opened the throttle, the decoder blew. So I think you need a load on the motor leads.
Bench testing a sound decoder without a motor or resistor connected should not cause it to burn up. If that happened, then there was something defective with the decoder.
Cacole I am not so sure of that. I hooked track pwr to the decoder using alligator clips and had the speaker wired. As I increased the throttle the sound increased as usual however when I got to about speed step 12 on my DT400 the main decoder chip started to get so hot I could not keep my finger on it and the sound started to distort? So not sure if it is a bad decoder (shouldn't be it was working in the loco a year ago) with no load I am not sure if speed step 10 is still the same speed as normal. I then wired up a small can motor I had laying around and with it hooked up to the decoder I could take it all the way up to 99 and the chip did not seem to heat up Mich and the sound did not distort. Not sure what all that means but it was fun until I shorted out one of the small chips on the decoder with a speaker wire. Now the chip has a nice burnt crater in the middle of it and the decoder is mysteriously quiet.
scubaterry Cacole I am not so sure of that. I hooked track pwr to the decoder using alligator clips and had the speaker wired. As I increased the throttle the sound increased as usual however when I got to about speed step 12 on my DT400 the main decoder chip started to get so hot I could not keep my finger on it and the sound started to distort? So not sure if it is a bad decoder (shouldn't be it was working in the loco a year ago) with no load I am not sure if speed step 10 is still the same speed as normal. I then wired up a small can motor I had laying around and with it hooked up to the decoder I could take it all the way up to 99 and the chip did not seem to heat up Mich and the sound did not distort. Not sure what all that means but it was fun until I shorted out one of the small chips on the decoder with a speaker wire. Now the chip has a nice burnt crater in the middle of it and the decoder is mysteriously quiet.
Sounds to me like the motor leads (or at least one of them) was shorted to something. If they were truly open, they could not draw current, hence no heat, hence no smoke escape.
Loose wire always seem to find a way to cause trouble.
Jeff But it's a dry heat!
I did some experimenting with SoundTraxx LC decoders and Tsunami decoders. I needed a
100 ohm 1/2 watt
resistor connected to the motor leads for the decoder to work properly. Never had any heating issues without a load. I think some are missing this bit of info. Many motors measure around 100 0hms.
Using a 100 ohm resistor has been discussed a number of times in some other DCC forums I belong. to
A simple Google search for dcc decoder resistor motor will bring results.
So many people forget Google searches.
scabbaterry etal,
Thanks for bringing this issue to light. I have used an Soundtraxx "LC" FM sound decoder with the ATLAS provided Decoder in my HO scale H15-44's. I want to retain the great class lights that you can not replicate in a normal (?) decoder.The sound decoder provides sound only, I did not use a "load" on the power to the motor leads on the "LC". I have not burned up the "LC" decoder but it sounds like they could "overheat"?
The "LC" has no "back EMF" etc so I am not sure it looks for any feedback on motor load. Just the same I know heat and electronics don't mix and will try a 100 ohm load. Anyone else have experience here?
Thanks again, Chris
I am running a HO steam engine with a Digitrax DZ125 in the engine and a SoundTraxx LC sound decoder in the tender. I put a 100 ohm resistor on the LC motor leads and the sound is just fine.
Hmmmmm, I have tested Soundtraxx Tsunami decoders with only the track power leads hooked up with no problems. I made sure the other wires were no touching anything. So if you need say a 100ohm resistor across the motor leads to simulate the motor, what happens if the motor on the unit opens up and there is no resistance? Will the decoder burn up? Same with a bad motor lead that becomes an open, will the decoder burn up?
One more thing with my Intermountain AC12 that has a Tsunami in it from the factory. I tested it with the tender only to see if the sound was working as I had bought it used. It all worked just fine even though the engine itself was not hooked up physically or electrically. So the motor was not in the circuit.
True, if there is an open in the motor leads you shouldn't have any problems with heat.
However many decoders use the motor during programming. If there isn't a load on the motor leads it may not accept changes to the programming.
Springfield PA
scubaterry I have a Soundtraxx Sound decoder I would like to test outside of the loco. Would I have to load the motor leads on the decoder with a resistor to get it to respond to my throttle? If so what would be a good resistor value?
You don't need to do this. Just attach alligator leads to each bare motor wire and set your volt meter to DC Volts and test on the main with address 3. You should see a change in voltage as you increase the throttle. Do NOT short the motor leads together. Do NOT turn on back emf.
Scratch everything I said. Just hook up the motor. If you didn't hook it up right, you'll get a failure on the cab when you try to program it. The decoder uses a motor pulse to acknolege program success. If you hooked it up wrong, it won't signal anything and your cab will show a failure.
Although in ALL honesty you should probly hook up ALL your wires then test for two reasons:
1) If you hook up additional wires to a socket later, you run the risk of accidently breaking off an older solder joint. (For example you test the motor leads, they are okay. Next you wire up lights, but accidently break motor leads while doing it...how would you know until you test it again?)
2) Exposed decoder wires can be a hazard. I was testing my motor functions and my speaker connections were not isolated when the speaker frame touched the track. It shorted and blew out the audio amp. (That was an expensive lesson)
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Hamltnblue True, if there is an open in the motor leads you shouldn't have any problems with heat. However many decoders use the motor during programming. If there isn't a load on the motor leads it may not accept changes to the programming.
True and False at the same time.
A motor movement is an acknowlegement to the command station that the command took. The command station looks for a "load" on the tracks which is signaled by the motor load. If it doesn't see this, it assumes the command failed and will give you an error on the cab. However if motor is not hooked up, then the command MAY have taken, but you would never know for sure. It varies by the DCC manufacturer. For example, trying to program a long address is setting of two CV's. If the first one fails on some DCC mfg's cab's then it will not try to program the second CV. (Lenz has this behavior with Athearn Genesis locos)