I have a sound/motor decoder that I'd like to use for sound only. I'd like to clip the motor leads and then piggyback the decoder to another motor-only decoder. I am told that I need to attach a resistor across the former motor leads so that I can program the decoder. 100 ohms was suggested.
I don't want to remove the resistor so that I can program the decoder address at the same time that I program the motor decoder's address, plus making any other changes without having to remove the loco shell.
My concern is that if the resistor is left in place it will get hot as speed/voltage increases and possibly cause shell damage.
Any way to get around this, or am I concerned about nothing?
Thanks
The resistor used should be rated for at least 1/2 Watt, and preferably 1 Watt, to avoid the heat problem, and it can be permanently connected across the motor leads. The higher the Wattage rating, the larger a resistor's physical size will be.
You can program Vstart, Vmid and Vhigh to zero, or set the speed tables to zero. This will cause the decoder to send zero volts to the motor, regardless of speed. You will need to do this while the 2 decoders are separate, though, or the other motor-only decoder will not run the motor, either. Once in the shell, don't reprogram these values on the motor decoder.
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What kind of sound decoder ? Just curious as to why you wouldn't pull the original decoder and use the sound and motor control from the single decoder ?
Regardless, IF that's what you want to do, it's easier for programming if you give each decoder a unique address and then just MU them with your controller. If you need to program either one, just dial up it's address.
Mark.
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Mark R. What kind of sound decoder ? Just curious as to why you wouldn't pull the original decoder and use the sound and motor control from the single decoder ? Regardless, IF that's what you want to do, it's easier for programming if you give each decoder a unique address and then just MU them with your controller. If you need to program either one, just dial up it's address. Mark.
Maxman asked: If I set Vstart, Vmid, and Vmax to zero as Mr. B suggests, and then consist that decoder to the motor decoder, will the sounds rev up and down as the motor decoder gets more or less voltage to move the engine. Or will the sounds just stay at whatever they are for power up?
The manufacturer of the sound decoder IS relevant because some sound decoders won't work like you want - Loksound for example. They require feedback from the motor in order to syncronize the sounds to the engine movement properly.
But then, if you had a Loksound decoder, it would have the motor features you want anyway, so it's a moot point I suppose ....
Ok then, here's a trick for setting up two decoders for running and programming. Set up each decoder with it's own unique 2-digit address prior to installation in CV1. Then set BOTH decoders to the same 4-digit address which is stored in CV 17 and CV18.
CV29 dictates whether the engine is to respond to a two or four digit address. Set CV29 to respond to a 4-digit address and both decoders will respond to the same address. Set CV29 to respond to a 2-digit address and you can program each decoder separately based on the two digit address. Bit 5 (Value 32) in CV29 controls the 2/4 digit addressing, on for 4 digit and off for 2 digit.
maxman...I am told that I need to attach a resistor across the former motor leads so that I can program the decoder...
Altohugh commonly believed to be true, this is not so. Decoders will program fine with no load on the motor output (at least the ones I've tried will). The decoder uses the load to acknowledge the programming command, but the programming will actually take place without the load. This will cause some command stations to report an error since the command station never sees the acknowledment from the decoder, but that does not mean the programming did not take.
This can make it more difficult to program an extended ("4 digit") address because it takes three separate writes to program an extended address: two for the address and one to enable it. Some command stations will stop after the first write because it does not see the acknowledement pulse. The solution for this is to calculalte the CV values you need to program and do them individually.
CSX Robertmaxman...I am told that I need to attach a resistor across the former motor leads so that I can program the decoder... Altohugh commonly believed to be true, this is not so. Decoders will program fine with no load on the motor output (at least the ones I've tried will). The decoder uses the load to acknowledge the programming command, but the programming will actually take place without the load.
This throws a different light on the subject. If no resister is required, thn I should be able to just parallel the decoders. Thanks!
Without the resistor, the decoder is not going to have a simulated motor load and the sound probably won't change with the different throttle settings.
cacoleWithout the resistor, the decoder is not going to have a simulated motor load and the sound probably won't change with the different throttle settings.
It was suggested that I set Vmin, Vmid, and Vmax (assuming that decoder has Vmid and Vmax - I think it does not) to zero. If I do this, then there will be no voltage output to the resistor/motor. Would this not be the same as having the motor leads cut?
If so, then I'm back to the 100 ohm/1 watt resistor again, am I not?
I guess the question is what causes the sound to rev up and down. I know it is not the decoder input voltage because that is constant. So somewhere in the circuitry there is something that lets the sound portion of the decoder know what it is supposed to do. If the controller causes the decoder to increase the voltage at the motor leads I would think that the voltage anywhere upstream of the motor leads would also increase. Then again, if current flow is needed to make this all happen I can see where there won't be any of that without a resistor/motor.
I suppose best way to find out would be to connect the decoder to the track without a motor and see exactly what happens.
DO tell us what decoder this is. I have an old SOundtraxx LC decoder in a dummy F7 B unit. Without a resistor on the motor wires it didn;t want to program on the program track, but ops mode works fine, and the sounds rev up as expected based on the throttle even with nothing connected to the motor wires. The sounds on those are not dependent on the motor load or any BEMF (doen;t have BEMF anyway - or even high frequency drive) Other sound decoders are different, and need the load (I wouldn;t set 2-6-5 to all zero, I'd set CV2=0, CV6=1, and CV5=2. Or set a speed table. All 0 in the 3 stepCVs usually means the default, which is a flat speed curve from 0 to full voltage).
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rrinkerDO tell us what decoder this is.
Okay. It is a MRC 0001643 Sheer Brilliance mini HO EMD Modern Switch Diesel. It does not support CV6 (Vmid). It supposedly supports CV5 (top voltage), but I never could get that to work. There are three built in speed curves, but it does not support the 28 speed step programming. CV 3 and 4 (acceleration/deceleration) are supposedly supported, but I don't use those CVs. I see nothing that mentions BEMF.
As I mentioned above, I like the sounds it makes, it hasn't smoked, and most importantly it is paid for. So if I can parallel it with one of the newer NCE decoders that I have on hand I would be happy.
Based on the decoder combination you have, I would say the majority of us are just making assumptions on what should work and what shouldn't. Based on the responses, it doesn't sound like any of us have done it successfully with an MRC decoder.
Soooo .... just wire it up without the resistor and see what happens. If it won't program or function properly, add the resistor. If you find the resistor getting too hot, go to a higher wattage. It's either a matter of it works or it doesn't, really can't see damaging anything.
What I've done when adding a sound-only decoder to an engine is put the motor & lights decoder in the engine and program it to run the way I like, then use alligator clips to connect the sound decoder leads to the programming track (a sidetrack on my layout) and program it with the ID no. of the engine. Then I can run engine and program the sound decoder so it matches up without affecting the regular decoder already in the motor.
p.s. does this decoder support CV 2, 5 and 6?? I don't use speed tables but have been able to speed match my engines just using CVs.
wjstix What I've done when adding a sound-only decoder to an engine is put the motor & lights decoder in the engine and program it to run the way I like, then use alligator clips to connect the sound decoder leads to the programming track (a sidetrack on my layout) and program it with the ID no. of the engine. Then I can run engine and program the sound decoder so it matches up without affecting the regular decoder already in the motor. p.s. does this decoder support CV 2, 5 and 6?? I don't use speed tables but have been able to speed match my engines just using CVs.
Only way to be sure if it needs a motor load on the sound decoder is to just try it. It can't hurt anything. Worst case, the sounds won't change as the speed is increased, but not having a load on the motor output won't fry the decoder. More likely, the sounds will work fine, but there may be issues in reading back CV values on the program track.