Digitrax Issue - "singing" moving between main lines

[peteski]

I'm not very familiar with Digitrax wiring, but it sounds like the singing was occurring when the loco was connecting both power districts while it was crossing the gap between them (on both rails).  Since the all the wheels on each side are electrically connected, the loco itself is like a "traveling shunt". Same applies to passenger cars which have all-wheel pickup for interior lighting (like Kato cars).

If you still had the original configuration I would have been curious to connect (short) the rails between the districts (one at  a time, then both) and observe when the singing starts.  Using a test leat d with alligator clips (or even just a piece of metal like a coin on its edge). Short the gap between the districts on the south rail only. Then only on the north rail.  Did either connections  cause the singing?

 Then connect both sides (north and south). That should cause the singing and the extra current flowing.  To me that shows that there is likely voltage imbalance between the boosters. Or possibly slightly different shape of the DCC signal waveforms (although that is unlikely).

[Bill H]

FWIW, I have heard of reported issues specifically with the 240+ when all the hardware connected to the DCS is not updated to the absolute latest firmware. I mean everything that is on the loconet - even down to UPs and throttles. I would update all the firmware first if not updated and then continue to debug. Hope that helps.

[GaryHinshaw]

I have a DCS240 with a DB150 booster (not 220) and I recently noticed that they put out different voltages: 12.9 V for the 240 and 11.9 V for the 150 (both are set to N scale on their voltage toggles).  Mine are fed by two different power supplies*, but the voltage trim for N scale may be a bit different in your two units.

RE the singing: I'm going to guess that while traversing a crossover, the loco gets power from one booster on one rail and the other booster on the other rail.  If the voltages are mismatched like mine are, this would give a DC component to the DCC voltage getting to the decoder, which could produce a weird effect like you're seeing.  If that is the cause, you could eliminate it by not having staggered gaps between the power districts.


Edit - NVM.  If I dial up address 0 to run a DC loco (i.e. apply DC to the rails), my DCC locos do not sing.  My question below about the single power supply still stands though.

-gfh

* By the way, why do you have a booster if you're feeding both stations off of one power supply?  I thought the point of a booster was to add more power to the layout so you could run more trains at once.  Why not run the whole layout off the DCS240?  Unless you have frequent shorts due to derailments and/or operators running against turnouts, the booster isn't really doing much for you except isolating the two mains, i.e. acting as an (expensive) circuit breaker.

[peteski]

Edit - NVM.  If I dial up address 0 to run a DC loco (i.e. apply DC to the rails), my DCC locos do not sing.  My question below about the single power supply still stands though.

That is because every DCC decoder derrives its power from its internal bridge rectifier, so even when the DCC signal becomes asymmetrical (there is a DC component) the sum of the energy in the positive and negative parts of the waveform is still close to 100%. Regardless of the polarity of the waveform, the (full-wave) bridge rectifier always produces the correct polarity voltage for the decoder.