DCC Decoder Use With DC or Removal ?

[chris-shay]

I'm after a bit of advise so hopefully the collective brain out there can help.

 

I recently bought (at Warley) a second-hand Atlas HO gauge C424 with the box advertising it as being DCC fitted.

The loco doesn't look like it has ever been run much and I was wondering whether it would run in DC mode on a layout using a Gaugemaster hand held controller (I don't have any DCC facilities) - I've read that they don't like feedback controllers?

 

Failing that, to convert it back to DC, do I just need to disconnect the decoder and insert a blanking plug in the 8-pin socket?

And are the blanking plugs available all the same as I'd have to get one as there's not one with the loco.

 

Any help appreciated!

 

Chris

[RAF96]

The likes of Peters Spares and New Railway Modellers Shop sell blanking plugs but your local model shop may have one they would give you.

 

You can make your own as all the plug does is link each motor brush to a track pickup and a directional light.

 

 

Rob

Edited December 7, 2017 by RAFHAAA96

[Phil S]

When 'electronic controllers' first appeared, and  with feedback, like Zero-1 = the dcc of the day, they (or the ones I had) were based around mains frequency - ir 50/100Hz -- often relying on the 16Vac to providee their timing.  The speed control was energy efficient by controlling the width of the pulses . and the feedback occured in the gaps when the motor ran on, and therefore was a generator, putting voltage (a small voltage) back onto the track ... which in turn was then measured by the controller which could then adjust the pulse width to maintain speed..(and direction)..

 

Early dcc decoders also used these low pulse rates  - until 'silent' decoers arrived on the scene .... replacing the low frequency buzz and cogging of the motor with smoother drive which was also quieter then the sound output !!

 

Some controllers are available with a 'true analogue' mode = in which a smooth variable voltage is output - and these are ideal for dcc-fitted locos to run on analogue layouts because, once the voltage reaches abot 5V the proicessor in the decoder turns on, and measures the polarity and amplitude of the incoming voltage .... and thereby controls the loco motor .... converting 5-12V input range into 0 to max speed as programmed into the decoder..      IF the track voltage FA:LLS TO ZERO then the processor turns off, and everythiong stops until th enext time the processor sees enough voltage on the track (whern it reaches 5V again) .... with a half-wave rectified dc, this would occur 50x a second - but even with an unsmoothed full-wave rectified output from eg a H&M Safety Minor of DC60 12Vdc supply,  where the voltage rises to about 28V peak 100x a second and then drops back to zero - the processor is continually 'reastarting' and behaviour is problematical if anything!!

 

The last Gaugemaster controller I tried ( a 4 output x 0-12V unit ) appeared to be pulse output (as expected for efficiency) when I connected it to a scope as paert of a test ... the scope was on 'Auto' setting and showed the nice variable pulse width.  What needed noting though, was the high frequency at which this was taking place!! - it was about 100kHz and nowhere near the 50-100Hz of old units ... the result was NO PROBLEM for dcc decoders on this analogue supply 8-)   (There may be a 'G Scale' controller from them which has a lower frequency switched pulse output - always best to ask them)

 

Interestingly, I recently made some cheap dcc track voltage monitors using 'in-car' dc voltage displays (0-30Vdc various colours)  ( a bridge rectifier on the input from 4 diodes, make a £3 voltmeter which reads 1.2V low )  -  no problem on smooth analogue outputs or dcc  BUT their display processors kept resetting when used on a pulse output (even the Gaugemaster) OR when Railcom was turned on on dcc - the gap was sufficient !   Obviously a small smoothing capacitor was needed after the rectifier 8-)

 

So it does depend on the design of the controller - and gaugemaster don't openly specify the operating pulse frequencies - and they may have varied over the years as the mdels were developed - so ask them for advice if in doubt.  Or simply test it.

[johnb]

I've some Atlas US locos ready fitted with DCC and for most of them the instructions indicate that operation on DC is already set up. I have run some on DC from a Gaugemaster hand held controller without problem. I simply put them on a DC operated layout and ran them, yes as Phil says above it does take a few volts to get them moving, but they are fine.

John