ntpntpntp said:
don9GLC said:
... the DCC control signals, effectively a high frequency ac signal on top of the 'power' 50 / 60 Hz. ...
Well, not
quite ... there is no 50/60 Hz AC component, just the DCC waveform (at around 10 KHz I think). You'll sometimes hear or read the expression "the DCC signal IS the power" .
http://www.dccwiki.com/DCC_Tutorial_(Power) < Link To dcc Wiki (power page)
You should be able to derive a usable DC supply from the track via a bridge rectifier and a smoothing capacitor, as has been said in other posts. Be mindful of what you power with it though: - for example if you drive point motors from the track supply and there's a short that trips out the command station then you loose point power too. Some DCC experts advocate a separate DCC bus for point control etc. I've gone down this route, but more for the reason that I want to keep the pointwork operational while feeding analogue DC to track when I wish to run unchipped locos or use alternative controllers (eg. if a mate brings a Train Engineer round to play!)
Well technically, you are quite correct, but it does not in my opinion help understanding. Much as I love Fourier Analysis and all the other mathematical techniques required to understand what is going on with a DCC signal, I suspect they will be lost on most members of this forum.
Without getting technical, a DCC waveform is nominally a square wave and it can be thought of as a power signal (actually 8.62Hz) and a control signal which has a range of higher frequencies. (and yes, its actually much more complex with 'long' zero bits). The NMRA standard specifies a minimum rise time which corresponds to 156.25Hz but in practice there will be (much) higher frequencies. These are electrically 'fragile' and can be affected by other devices connected to the track.
The risk in connecting 'homemade' circuits to a DCC track supply is that the effect on these higher control frequencies has not been tested and unexpected things can happen. Without doubt, the power from a DCC track supply can be used to supply auxiliary components, but there could be unexpected (sometimes random) effects, not limited to loss of control of locos, damage to the command station and radio / TV interference.
Its simple and easy to avoid this risk.
On the subject of a separate DCC bus to power auxiliaries, as far as I am aware, normally every auxiliary component is connected to the bus through an interface unit, designed for connection to the DCC system. So even in this case measures are taken to avoid interference.
Its also extremely wasteful to load up a DCC command station with non DCC devices which could instead be connected to a simple power supply. Basically more load, equals more heat, equals shorter lifetime.
The simple rule should be use DCC power for DCC, and nothing else.
I'm sorry if this seems to be laboring the point, but I originally tried to respond to a 'simple' technical question with a simple 'non-technical' answer. I apologize for being 'economical with the truth' but its not Ohm's Law or anything like as simple