Potrail2378 Posted November 6, 2020 Share Posted November 6, 2020 Hi, I have converted several loco's to DCC but I'm stumped with my latest venture. I couldn't get any LEDs to work, and when I touched the 1Kohm resistor, it was red hot. I measured the voltage and it was 42vdc! I left it for an hour or so and checked the voltage again, this time it was 26vdc. Is my standard Hornby decoder beyond repair?Thanks in advance. Link to comment Share on other sites More sharing options...
Rog RJ Posted November 6, 2020 Share Posted November 6, 2020 What controller are you using? What is the voltage on the track? (use the AC range on your meter) Link to comment Share on other sites More sharing options...
96RAF Posted November 6, 2020 Share Posted November 6, 2020 Hornby decoders are rated for max 27v so it is marginal if you have permamently damaged it or not.Possibly if its still working the life has been reduced Somewhat. I wonder how you managed to get that potential out of a decoder as the internal gubbins should regulate it down to 12v. As Rog asked - it makes me wonder what the track voltage was. Link to comment Share on other sites More sharing options...
ColinB Posted November 6, 2020 Share Posted November 6, 2020 I have great difficulty understanding how you got 42 volts DC, unless you got some capacitor voltage doubling effect. I think the max voltage for DCC is 18 volts, but I am not certain on that. The first question is did you smell smoke and the second is does the loco sit on the track without causing a short ( the controller trips out). If neither of these two has happened you might be lucky, normally from my experience and I have had a few die on me, you normally get those two effects, normally the bridge rectifier diodes fry themselves and eventually cause a short circuit. First thing to do is go back to dc ( I bet you didn't use a socket, that is why I always suggest using one) and see if the loco still works without the decoder. To me it sounds like something is wrong with your DCC controller, but I find that hard to believe. Link to comment Share on other sites More sharing options...
Chrissaf Posted November 6, 2020 Share Posted November 6, 2020 Nobody has yet asked the most important question. Which is, across what two points was this 42 Volt DC and 26 Volt DC actually measured? Across the resistorAcross the LEDBetween the Blue wire and somewhere else.Across the wheels The list goes on.No suggestive deductions can even be really attempted until one knows the answer to the above, else it is just all speculation. Link to comment Share on other sites More sharing options...
ColinB Posted November 6, 2020 Share Posted November 6, 2020 I can't see anywhere on a decoder that you would get 42 volts. DCC is about 18 volts if I remember, I did check the specification but I couldn't find it. Even if it was measured peak to peak that makes it 21 volts plus or minus, which is way out. As I say the only way I could see you would get that voltage is if you measured some noise spike. Link to comment Share on other sites More sharing options...
Potrail2378 Posted November 6, 2020 Author Share Posted November 6, 2020 It's a Hornby Select, it's measuring 15.5 vac across the rails. I'm now getting a constant 26vdc across the blue wire and the green wire. There is no smell of smoke, and yes, I am using a socket. I have tried three different decoders, all giving the same results. Link to comment Share on other sites More sharing options...
ColinB Posted November 7, 2020 Share Posted November 7, 2020 I hope you haven't blown up all three. Ok, do a continuity check between the green wire and the track with no power connected. Check that the green wire is actually connected to something, also check the resistance value of that resistor yhat was very hot. Does it still work on DC ? Link to comment Share on other sites More sharing options...
Fishmanoz Posted November 8, 2020 Share Posted November 8, 2020 Remember the green wire is switched -ve. When switched on (via F1), you get -12 volts v the always on blue positive. So with it switched off via F1 or without track/decoder input voltage, it will be floating and what you read versus anything else will be anybody's guess. So power your decoder, switch the green on and measure v blue. You should get - 12 volts. Link to comment Share on other sites More sharing options...
Potrail2378 Posted November 8, 2020 Author Share Posted November 8, 2020 Thanks for the help, there must have been a short somewhere - maybe the green wire to a rail? Anyway, it's sorted now. I have put directional lights in now, and am waiting for my sound decoder to arrive. Link to comment Share on other sites More sharing options...
96RAF Posted November 8, 2020 Share Posted November 8, 2020 Are you saying it could have been operator error and not a decoder problem. Link to comment Share on other sites More sharing options...
ColinB Posted November 8, 2020 Share Posted November 8, 2020 He didn't say, he also didn't say whether he blew up the other 3 decoders. If the green wire was shorted to track, they would all be dead. Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now