Apologies if this has been discussed before; I’ve searched for but not found prior discussions. If I use a mobile decoder without a motor attached, do I need to simulate the normal load of a motor for the decoder to operate properly? (I assume this would mean a resistor in place of a motor, but what value?)
Examples of this situation: using a few extra mobile decoders I have for passenger car lighting only. Or: keeping an older loco’s original mobile sound decoder in place for sound purposes (disconnecting the motor from it), and adding a newer mobile-only decoder for better motor control (yes, there might be added issus of having the sound sync with speed properly, and programming gets more complicated, etc.).
NCE’s website mentions adding a 47K 1/4 watt resistor to simulate motor load for one of its mobile decoders if it is used for lighting only, but I’m wondering if that’s generic information for any decoder, or perhaps specific for the particular NCE decoder mentioned in NCE’s help files. I’ve not found any guidance yet from other decoder manufacturer websites.
The problem with using a lower value similar to an actual motor is then you need to use a fairly high wattage resistor, which can get hot, unless you also remember to go in and program the speed table, or at least CV5 max to something low. If CV2 is 0, then CV5 can be as low as 1.
Anything in k’s should be fine and not get hot. The whole need is to put some sort of a load pulse on the program track to ack and read back CVs - the decoder will normally pulse the motor. NCE’s value should be fine but smaller will be OK too.
“Like an actual motor” are resistors of say 100 ohm. You’d need a 2 watt resistor to handle full track voltage, and it would be generating right at 2 watts of heat, too. a 5 watt would be better at 100 ohms. ANd that much heat enclosed in the loco or car shell is not good. There’s no reason for it, a larger resistor won’t get nearly so warm and will still do the job.
It’s been a while since I did this, but my recollection is that a resistor is only needed to program the decoder, even if you’re just setting the address.
I would disconnect the resistor after programming, since you shouldn’t be applying any power to the “motor” anyway.
That’s what I’ve always done. A 100 ohm resistor for programming, then remove the resistor for operation. Chances of me having to re-program again down the road are pretty slim. You could even leave the resistor in place as long as you don’t advance the throttle while that particular address is accessed.
Thanks for all the helpful replies. One follow up question: what would happen if the resistor is left in place and the throttle is accidentally increased off of step 0? Heat problems? Decoder damage? Something else? Nothing? I’m wondering about the convenience of leaving the resistor in place versus any risk that entails. Thanks very much.
But the apparent voltage at the motor terminals of the decoder increases. If the resistor is left connected, everything will be fine if the decoder is set to an absolute minimum top speed, with CV5 set to 1 or 2. Then even if you acciently turn it to full throttle, the resistor won;t get hot.
I did that some years ago. I adjusted one or two CV’s. Don’t remember which ones so the resistor did not get hot. I used a Tsunami Micro. Bruce Petrarca, Mr. DCC use to have a DCC site with the explantion. His site is gone.
I had put a DZ125 in a Mantua 0-6-0, turned it around to become a 2-6-0 oil fired cab forward and put a Bachmann Vanderbilt oil tender behind it with the micro in it. It worked very well.
I found photos of a NG cab forward 4-4-0 made around 1900 I think.
NPC #21. Really crazy loco that had some serious design flaws, but it was the first in many things, not just the first cab forward. One of the first if not the first locos designed as an oil burner, and the first to use a marine boiler, which explains the really odd appearance. Then tender was insteresting - two tanks on wheels, one water, one oil.
Perhaps a little bit the inspiration for the Kemtron cab front to convert a Lil Joe to a cab forward.
Got any pictures of that Mantua cab forward conversion?
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