Hello, long time reader/first time posting. I have a question about measuring the DCC voltage on the frogs of my Micro Engineering turnouts. I'm building an around the walls shelf layout and have some of the track and wiring completed. The turnouts in my staging yard are operated by servos programmed in an Arduino. When a pushbutton is pressed to switch the turnout, the Arduino tells the servo to travel to the other end of its swing. At the same time the Arduino changes the state of an output tied to a 4 channel relay board. The contacts of these relays are what change the polarity of the frogs. I measure appx 13V AC between all the rails but only measure 4.8V AC from any frog to a rail. Is that really the voltage I'm feeding the frog or do the solid state contacts of the relays prevent me from reading the full voltage with my Fluke DVM? I've ran a locomotive through these turnouts a dozen times and it ran perfectly but am still perplexed by these odd readings.
Any help would be most appreciated.
By solid state contacts do you mean some kind of electronic logic relay or an old style relay with contacts that physically move?
I have found that I can get a low voltage reading from a rail that is not connected to anything when trying to read DCC voltage with a meter not designed for DCC.
Leonard P. ThusdogI measure appx 13V AC between all the rails but only measure 4.8V AC from any frog to a rail. Is that really the voltage I'm feeding the frog or do the solid state contacts of the relays prevent me from reading the full voltage with my Fluke DVM?
without any load, that's far from acceptable.
i suggest you measure the votlages supplied to your relays and from your relays to determine where there is a drop.
can you provide a part # to the relays?
greg - Philadelphia & Reading / Reading
Leonard P. Thusdog ...I've ran a locomotive through these turnouts a dozen times and it ran perfectly...
...I've ran a locomotive through these turnouts a dozen times and it ran perfectly...
I'd stop measuring
Good advice -thanks
mvlandsw,
thank you for your response. I took your advice and discovered the problem was in my wiring. I had somehow forgot to connect the switching side of the relays to the DCC bus! You were right saying I could get a low voltage reading from a rail that was disconnected. Now that I've connected the power everything reads and runs good. Also you got me thinking more about my belief that the contacts were solid state. They're not. The Songle relays have mechanical contacts - I can hear them.
Welcome.
There are a couple of things that come to my mind. Measuring DCC voltage with a DVOM is problematic at best. It's not AC and not true DC. An old analog meter set on AC would be more accurate.
Depending on how the relays are configured. You may be just outputting switching voltage instead of track voltage out to the frog.
I made a simple test rig using a metal wheeled truck with a 16 volt micro bulb soldered to the pickups. Simple, short and easy. The brightness of the bulb and the short length of the truck let's me know if there are issues with wiring and frog gaps.
Pete.