colinayres1 Posted June 17, 2016 Share Posted June 17, 2016 Hi there I have recently been conducting a experiment by installing a dcc decoder to the track of my layout through a double pole double throw switch to allow the membership of our club to use all the advantages of Dcc but without forcing them at their age to convert their dated stock over to dcc. Experiment 1. Running a Dc loco on track, experiment successful, loco run smoothly and when track deliberately shorted controller cutout. Experiment 2. Two chips two tracks two separate feeds one train and a standard track to track crossover. Both chips had different addresses so I created a consist and checked they both operated in the same direction. Test worked well and I could go from track to track. Only one little glitch! There is a momentarily surge in voltage as I go form one to other which looks a little unrealistic. Have any of you got any idea's. Link to post Share on other sites More sharing options...
knitpick Posted June 17, 2016 Share Posted June 17, 2016 I am not really DCC savvy. But I would suggest that as the loco goes from the control of one chip to the other it is briefly powered by both chips. Double voltage will give double power and thus a surge. You should get the same effect if you powered the two circuits from different DC controllers. Link to post Share on other sites More sharing options...
colinayres1 Posted June 17, 2016 Author Share Posted June 17, 2016 Interesting point but surprisingly on pure dc, for instance two controllers both turned to same speed position you don't get a surge. A controller must have some kind of smoothing circuit which a decoder might not. But then there is cv's maybe tweaking them might achieve a change. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted June 17, 2016 Share Posted June 17, 2016 This is the direct equivalent of an electronic - typically PWM - DC controller. I'd view it as a temporary workaround only (I have done it myself when without a DC controller and wanting to test a loco on DC). Shorting a decoder's motor output won't do much for its longevity in my experience, even on decoders that claim short circuit protection. You lose three of the greatest advantages of DCC instantly: No longer have a constant circa 15V alternating supply on the rails which makes pick up so much more reliable and reduces rail dirt. No customised set up on every loco for much improved control and - if wished - a standardised set up; with opportunity for control of other functions on the loco. The layout has to be sectioned to allow independent control of locos, exactly as with any DC system: a regular switched section layoput control set up will eliminate the surge resulting from temporary supply from two decoders. Link to post Share on other sites More sharing options...
RMweb Premium JDW Posted June 17, 2016 RMweb Premium Share Posted June 17, 2016 I can't help on why it might surge, the answer above seems plausible, but just wanted to add that this seems a very good idea. OK, you loose the advantages of proper DCC operation but at least on a small layout which would only have one DC controller anyway, it could be a good way of testing or using non-DCC locos without having to have a DC controller to hand. Link to post Share on other sites More sharing options...
RMweb Premium Grovenor Posted June 17, 2016 RMweb Premium Share Posted June 17, 2016 The surge comes about because the decoder produces a stream of full voltage pulses and the motor effectively sees an average voltage depending on the relative on and off time. The second decoder produces another set of pulses so the motor sees twice as many pulses and thus a higher average voltage. Each decoder has an independant timing setup so the pulses are not synchronised. Regards Link to post Share on other sites More sharing options...
colinayres1 Posted June 17, 2016 Author Share Posted June 17, 2016 Well all that was very interesting thank you. So from this although it's irregular to use dcc in this way it is possible to have a dcc controller control both dc and dcc locos and maybe a future experiment delving into the depths of pulse width modulation to lessen the surge. Has anyone got any ideas how I could lesson a surge getting back to the chips? Link to post Share on other sites More sharing options...
colinayres1 Posted June 17, 2016 Author Share Posted June 17, 2016 Well all that was very interesting thank you. So from this although it's irregular to use dcc in this way it is possible to have a dcc controller control both dc and dcc locos and maybe a future experiment delving into the depths of pulse width modulation to lessen the surge. Has anyone got any ideas how I could lesson a surge getting back to the chips? Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted June 18, 2016 RMweb Premium Share Posted June 18, 2016 Make sure you don't have anything like a Relco or high frequency lighting connected to the track, otherwise the chips will become toast. Link to post Share on other sites More sharing options...
colinayres1 Posted June 18, 2016 Author Share Posted June 18, 2016 I must admit I cooked a chip, I have two locos the same and accidentally put a chipped loco on a chipped track, even with dc on it fried the one in the panel. Link to post Share on other sites More sharing options...
RMweb Premium Grovenor Posted June 18, 2016 RMweb Premium Share Posted June 18, 2016 Has anyone got any ideas how I could lesson a surge getting back to the chips? See post #4 above. Regards Link to post Share on other sites More sharing options...
knitpick Posted June 18, 2016 Share Posted June 18, 2016 Picking up on Post 3, if you put 2 1.5 volt batteries in parallel - your still get 1.5 volts; you don't get a surge. However very few DC controllers actually deliver a constant voltage for a specific setting. And the electronics between the variable resistor behind the control knob and the output terminals will also have a resistance. So with two DC controllers in parallel, the loco motor "thinks" "Oh I'll take half current from each controller". At which point the controllers "think" "The voltage balance has changed (because actually the current has altered) - need to increase the voltage to the track". Hence a surge. OK a bit simplistic but the apparent resistance balance has changed due to the motor demanding less current. Introducing feedback (which I believe some chips have) and Pulse Width Modulation just complicates the controller behaviour as this turns off the voltage briefly. Feedback to check if the loco's motor is slowing down and needs more voltage. PWM as that was designed to feed 12volt bursts - short bursts with long gaps for slow speed - long bursts with shorter gaps for higher speed. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted June 18, 2016 Share Posted June 18, 2016 Has anyone got any ideas how I could lessen a surge getting back to the chips? Will you believe anybody who tells you that this vry same thing happens if two DC controllers temporarily supply the same loco in exactly the same situation? Switched sectioned layouts were developed to solve this and other problems a lifetime ago. That's your solution: you are using DC control, not DCC, and so you need to do things the proven DC way... Link to post Share on other sites More sharing options...
colinayres1 Posted June 20, 2016 Author Share Posted June 20, 2016 Thanks again for information, I'm investigating using transzorb bidirectional diodes to protect the decoders before I go any further with the experiment. If the transzorb it might be a idea for every decoder in the fleet aw they stop power surges from damaging the chips Link to post Share on other sites More sharing options...
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