DCC Myths and Untruths
Posted: Wed Feb 16, 2022 4:33 pm
1) DCC is a two wire system. While partly correct in reality there will be wiring from the rails to the DCC Bus pair if used and to all accessory decoders, then from the decoders outputs to the items they are to operate.
2) A DCC loco will run on DC (Analogue) track power. Another partly true statement but it will depend on whether CV29 has had DC operation turn On in the decoder. Many DCC users will turn Off DC operation as it can lead to uncontrollable runaways, so always check with the supplier when obtaining a new or second-hand DCC fitted loco.
3) A DCC Bus pair wired as a Ring will cause data signal issues. Totally untrue at the frequency DCC operates, you would probably need a layout nearing 1/2 mile long before any possible problem was encountered.
4) I can run a DC loco on a DCC system. Another partly true statement and not recommended practice. Many DCC systems do not allow a DC only loco to operate. Some however do offer the chance of running one DC loco via address number 0 (Zero). This is not a wise option though! By placing a DC only loco onto DCC powered rails and leaving it stationary will run the real risk of the motors coils burning out due to the rapid changing of polarity of the DCC waveform causing the motor to minutely hunt back and fore, this causes the motor coils to heat and eventually burn out!
5) DCC Bus Filters are a waste of time. Untrue as the filter (Its not a snubber!) helps remove all spikes that occur on the DCC bus or rails. These are caused usually by a short circuit occurring. Fitting Bus filters to the bus pair or rails will remove or smooth out these spikes.
6) DCC is AC. Technically not true, as DCC is a square wave form rather than a sine wave that AC is associated with. Its possibly best described as a Modulated Pulsed supply with encoded Binary data. It operates at around 8KHz (8000 times a second).
7) Points (Turnouts) need to be DCC compatible to work. Not true, any point that works on DC will work on DCC. There are modifications to points that allow Insulated frog points to provide power in both directions regardless of the points actual position. Live frog (Electrofrog) points can be modified to improve power and data flow through the point.
8) The 'Coin across the rails' short circuit test will destroy my DCC system. Untrue. The DCC system internal electronics sense the rise in current caused by the short and trip the output power in microseconds. The Coin across the rails test carried out around the layout at many places proves the integratory of the wiring and ensures the system will trip immediately. Any delay in tripping should be immediately investigated and corrected.
9) I wish I could use conventional point/accessory operation on my DCC layout. There is no reason at all why DCC can't just power the rails and drive the trains, while all accessories such as points or signals etc are controlled and powered by conventional (Analogue) means. Just do not allow the two systems to connect together.
2) A DCC loco will run on DC (Analogue) track power. Another partly true statement but it will depend on whether CV29 has had DC operation turn On in the decoder. Many DCC users will turn Off DC operation as it can lead to uncontrollable runaways, so always check with the supplier when obtaining a new or second-hand DCC fitted loco.
3) A DCC Bus pair wired as a Ring will cause data signal issues. Totally untrue at the frequency DCC operates, you would probably need a layout nearing 1/2 mile long before any possible problem was encountered.
4) I can run a DC loco on a DCC system. Another partly true statement and not recommended practice. Many DCC systems do not allow a DC only loco to operate. Some however do offer the chance of running one DC loco via address number 0 (Zero). This is not a wise option though! By placing a DC only loco onto DCC powered rails and leaving it stationary will run the real risk of the motors coils burning out due to the rapid changing of polarity of the DCC waveform causing the motor to minutely hunt back and fore, this causes the motor coils to heat and eventually burn out!
5) DCC Bus Filters are a waste of time. Untrue as the filter (Its not a snubber!) helps remove all spikes that occur on the DCC bus or rails. These are caused usually by a short circuit occurring. Fitting Bus filters to the bus pair or rails will remove or smooth out these spikes.
6) DCC is AC. Technically not true, as DCC is a square wave form rather than a sine wave that AC is associated with. Its possibly best described as a Modulated Pulsed supply with encoded Binary data. It operates at around 8KHz (8000 times a second).
7) Points (Turnouts) need to be DCC compatible to work. Not true, any point that works on DC will work on DCC. There are modifications to points that allow Insulated frog points to provide power in both directions regardless of the points actual position. Live frog (Electrofrog) points can be modified to improve power and data flow through the point.
8) The 'Coin across the rails' short circuit test will destroy my DCC system. Untrue. The DCC system internal electronics sense the rise in current caused by the short and trip the output power in microseconds. The Coin across the rails test carried out around the layout at many places proves the integratory of the wiring and ensures the system will trip immediately. Any delay in tripping should be immediately investigated and corrected.
9) I wish I could use conventional point/accessory operation on my DCC layout. There is no reason at all why DCC can't just power the rails and drive the trains, while all accessories such as points or signals etc are controlled and powered by conventional (Analogue) means. Just do not allow the two systems to connect together.
