RailPro and DCC Modules Compatability

[G8B4Life]

I got an email back from RE.

Because I can't be bothered writing up a story I'll just quote my whole question and RE's answer, without the entire bit on AC and dirty rails which RE put onto the end.

My question, involving shameless plug for RPUG:

We are having a discussion on the RailPro User group in relation to a member who wishes to build modules for both home and club use. He uses RailPro at home and the club uses DCC. The discussion has centred on that he might have to add DCC specific items to his modules like frog juicers, which we know do not work with RailPro's pure DC.

We also know that an LM can utilise a DCC signal for power. Our question is thus: Does the "DCC signal" that an LM can utilise for power have to be correctly coded DCC packets (0's and 1's) or could the LM utilise a raw DCC waveform (eg, all 0's or all 1's) of the correct duration and amplitude as specified for DCC?

Being able to use a generated raw DCC waveform would allow the member to add club mandated DCC specific items while not having to purchase a DCC system to power RailPro at home.

RE's answer

As long as the '1's and '0's follow the DCC electrical specification it would not make a difference to the RailPro locomotive modules. However, there are other options than making your own DCC booster.  Our AR-1 can be used to power the frogs.  You can also use a tortoise or similar slow motion machine and wire the frogs with the extra electrical contacts on the tortoise.  We find that insul-frog switches work fine for us and they do not need to do any wiring.  If you put a DCC signal on the track it will causes your wheels to get dirty much faster than when running a DC power supply (like our PWR-56).  In our testing we have needed to clean DCC powered track 4 times as often as an analog powered track**.

So there we have it, if anyone had any "dumb" (cannot decode the information in the signal) DCC equipment installed on a layout they could build our own DCC waveform generator without the expense of a DCC system for power and off they go. The next question is are DCC frog juicers actually dumb or not?

I took notice of RE's statement that their AR-1 could power frogs. Not sure if he was still talking DCC at that point but I don't think I'd risk it to find out but for DC it's a solution that I didn't think of; though at the cost of an AR-1 I still wouldn't be be using them to auto power frogs.

- Tim

[Alan]

Sort of knew that would be the answer. When you look inside an LM-1,2,3 the track power wires connect to four SMD power diodes that form a bridge rectifier. The DCC AC signal is immediately rectified into DC upon entering a LM. The LM is effectively being supplied PWM DC when operating on DCC. With a 50% duty cycle oscillator as a stand in for the DCC command/booster, the LM would see a 100% duty cycle PWM signal. No different than a DC power supply.

The AR-1 definitely will not work with DCC. The input side of the AR-1 is polarity sensitive (marked on the unit and called out on pg3 of manual) so feeding it the DCC AC waveform is out of the question. Plus, as you rightfully mention, it would be a very expensive frog juicer.

The DCC appliances on the market (juicers, occupancy detectors, and the like) are made to work with an AC square wave on the track. Providing the unit is not DCC programmable, there isn't any reason why the duty cycle or pulse width of the AC wave should make any difference. Ironically, it is this square wave that is at the root of the DCC dirty track problem.

[TwinStar]

I would caution against using insulated frogs if they module standard is Free-mo. They require powered frogs and will not accept insulated ones. Our group doesn't allow insulated frogs either.