dbrb2 Posted January 6, 2022 Author Share Posted January 6, 2022 I've run the buck fine from a DC bench supply, so I don't think it is overloaded....but perhaps it could be the diode speeds The DC PSU into the sprog is 12v, 3A so should be sufficient Link to post Share on other sites More sharing options...
Crosland Posted January 6, 2022 Share Posted January 6, 2022 What voltage do you get across the cap? Unlike the DCC input you can measure this with an ordinary DVM (it's a quick and dirty way to measure track voltage if you allow for the diode voltage drop. Link to post Share on other sites More sharing options...
dbrb2 Posted January 6, 2022 Author Share Posted January 6, 2022 Tested with a bench supply - still working with input at either polarity, 12v However, the output measured from the rectifier, measured across a cap, is only showing as 4mV when connected to DCC To rule out wheel pickup issues, I have wired the DCC cables directly into the rectifier input, with no change in behaviour Link to post Share on other sites More sharing options...
dbrb2 Posted January 6, 2022 Author Share Posted January 6, 2022 (edited) Ok. It's working... I think it was dodgy wiring. So my next job is to check absolutely everything :-) It does however seem to much up the DCC signal for all my other devices when running! Edited January 6, 2022 by dbrb2 Link to post Share on other sites More sharing options...
Crosland Posted January 6, 2022 Share Posted January 6, 2022 2 hours ago, dbrb2 said: It does however seem to much up the DCC signal for all my other devices when running! When wired directly to the tracks or via pickups? Fast diodes such as UF4001 or schottky diodes (inherently fast) might help, but shouldn't make a lot of difference for a single instance. (The problem is a normal diode looks like a short circuit for a very short time each time the polarity reverses. A fast diode recovers much faster). Try reducing the cap value or placing a small resistor (start at, say, 100 ohm) between the diode bridge and the cap to reduce the charging current. Link to post Share on other sites More sharing options...
dbrb2 Posted January 6, 2022 Author Share Posted January 6, 2022 Thanks @crossland - the interference was when on a short length of track with other trains. Yes, I can see that the recovery time of "normal" diodes might mess with the comms - I will try to remake the circuit with these diodes: https://docs.rs-online.com/a661/0900766b809285fd.pdf Which claim to have an ~50nS recovery time. The 2W10 I was using didn't have a published recovery time - but I suspect it was higher than this. Presumably the charging current should only affect the DCC signal if the cap is almost empty - and a high ciurrent causes the supply voltage to drop, confusing the DCC decoders? Either way, worth doing Weekend job i think! Link to post Share on other sites More sharing options...
Brian Posted January 7, 2022 Share Posted January 7, 2022 I've been showing LED carriage (and other uses too) lighting designs for some while. It may help? Link to DCC lighting section Link to post Share on other sites More sharing options...
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