Hornby 56 toasted by DCC ?

I mean exactly that. Stick an old Hornby model (with a Triang motor) on the track with the controller set at zero and you will hear the motor buzz.

(kim)

"Adrian B" wrote

I agree with your sentiment, but the loco is NOT a write-off, it's perfectly possible to buy a new armature - assuming of course that you've not melted the motor housing.

One the other hand the Tech-Cad option is worth considering, but one of my customers has fitted a slightly modified Bachmann class 37 chassis to a Hornby 56 and is *very* pleased with the results.

John.

"MartinS" wrote

Got to agree with Kim on this one, the *very basic* Hornby train set controllers do not seem to cut the power off completely when the control knob is at zero and a slight buzzing sound is audible.

John.

"Adrian B" wrote

I don't believe any standard British outline OO-scale ready-to-run locos are supplied with coreless motors.

I've got a rather nice kit-built Stanier 8F (from a DJH kit) which is fitted with a Portescap motor. This works superbly with a Lenz Gold decoder fitted, but I would never have considered using same without a decoder on DCC.

John.

It matters not whether the "system" supports a DC loco on address 0. The DCC track waveform is the same for a system that doesn't support address 0 and one that does when the speed for address 0 is set to 0. Neither DCC system is more likely to fry a loco than the other.

A difference that is crucial is the DCC track voltage, which does vary between systems and can often be varied by the user.

MBQ

A few valiant attempts, but no one has been able to explain how DC locos are driven on DCC, which uses an AC waveform. John comes closest when he talks about wavelength.

The DCC waveform has a forward half cycle (current flows one way) and a reverse half cycle (current flows t'other way). Normally both half cycles are equal length in time, there is equal current flow both directions and a DC motor will sit still. Actually it's trying to oscillate back and forth in time with the current flow but each half cycle is too short to produce any movement. if you simply vary the wavelength (and by implication the frequency) then there is still no movement. The average (loosely speaking DC) voltage across the motor is zero. Since the motor is stationary no Back EMF is generated and the motor is subjected to the full track voltage and dissipates a lot more power (cf stall current). Coreless motors with their low thermal mass are prone to burn out. Other motors may be harmed depending on their characteristics and the track voltage. They shouldn't be fried, but I bow to others' experience.

A similar situation exists with coreless motors driven by decoders. The decoder output is pulsed and you *must* use a decoder with a high frequency output. In this case the inductance of the motor smooths out the high frequency pulses so that the motor sees the average DC voltage and is not damaged.

To make a DC loco move on DCC, one half cycle of the DCC waveform is lengthened such that the motor passes current in one direction long enought to make it move. To reverse, the other half cycle is lengthened. The

The DCC signal consists of binary 1 and 0 bits. 1s have both half cycles nominally 58us, 0s have both half cycles greater than 100us and less than 10ms. Specifically, only those parts of the DCC waveform sending 0 are lengthened, hence the term "zero stretching". The clever part is stretching enough of the zeros by the correct amount to give the desired speed and smooth running. The average voltage across the motor is made either positive or negative by stretching one half cycle of some of the 0 bits.

MBQ

I was thinking in terms of product liability rather than convenience.

If a novice was to purchase an unchipped loco and leave it on a DCC energised track he could reasonably be expected to be compensated if the loco burned out as a result of that. Even more so now that Bachmann and Hornby produce proprietry DCC systems. I've yet to see an unchipped loco come with a prominent warning to the effect that it must never be placed on a DCC energised track.

(kim)

"Adrian B" wrote

I know that one or two people have used Bachy 25 chassis for uprating Hornby &/or Lima IC125 power cars, which is OK providing you don't want scale

John.

Just about to DCC my Bachy 25 chassis powered Hornby HST!! Took a bit of hacking about, but it looks like it'll do the job. Now to suss out the 37 powered 56!!

Cheers, Mick

We have a siding near the front of the layout that can be used to "show-off" stock. This is fitted with two switches to isolate it from DCC, so that a non-DCC loco can be parked there safely.

Cheers, Mick