I plan on using blumami decoder as a DC power supply for my layout and can’t decide if a 2 amp (HO/S) decoder will work or if I should spend the extra cash and go with a 4 amp G scale decoder. This will give me under layout sound as well as control via smart device. This will be a second cab to my control master 20. Thoughts? Bluerail has a video on how to do this and it is quite intriguing.
I would go with the G scale decoder, for it's higher current rating. Decoders usually drive only one motor, but in this application, it could be driving more than one (e.g. consisted) locomotive. Note that over-current sensing for a fixed motor-drive installation (such as the designed application of the decoder) would typically be only on one leg, since normally whatever current goes out on one leg to the motor comes back in on the other leg. Therefore, the decoder's motor output's over-current protection may not protect it from shorts to a separate cab with it's own power. Your existing Control Master 20 is rated to supply 100VA, or perhaps 5 amps at 20V (with potentially higher current at lower voltages), so shorts between the two 'cabs' could get pretty hot quickly. The old automotive lightbulb trick for limiting (and indicating) short circuit current on layouts may work well here.
Big Jake, I usually don’t run both cabs at the same time, will likely abandon the cord if it works well enough. I like your idea on the bulb trick.
My mistake, I thought you were going to set up multiple blocks with two cabs, which could be switched to control each block by either cab using SPDT (center-off preferably) electrical toggle switches. IIRC, NCE promulgated the light-bulb idea for short circuit protection and indication. It's not my idea, but it is a good one to share. With a DC system, the brightness of the bulbs, when running trains or in the case of a short, will vary with throttle setting, so it's not quite as effective for DC as for DCC.
