grob1234

Especially if they're 'into' DCC or say 'sat' instead of 'sitting' etc.

Similar to parents evening, Sir just needs to allow 5 minutes per person. Once time is up (Mo would be an excellent time keeper) the person would be escorted away. Easy?!

Definitely one of my favourite layouts. Well done to all the crew.

Unfortunately, that would require too much wiring for the benefit gained. I've definitely buggered the relay, it worked fine before hand. It does seem the CDU/Relay combination is perhaps not the one. Never mind, it was worth an exploration.

OK that's good to know about the CDU. And part 2 also makes sense as well. As you can tell, its all a learning process for me - I'll take your word for it that there's a large spike of reverse voltage. For me, in order to understand why things are as they are, its important to figure out where the excess voltage comes from, which you have explained. Thank you.

This is my theory too. At “rest” the cdu output is 23.4v or thereabouts, but I don’t know what it spikes to upon operating the switch. More than 23.4v I’d have thought, and yes I only have a basic multimeter, so I’m not surprised it can’t register the momentary voltage spike. The switches are (on) off (on) sprung to centre type SPDT type recommended for solenoid point motors. This is the annoying thing here… the test with a stable 12v supply produced exactly the results I was hoping for! So the theory and wiring was correct. With regards to relays, could it be possible that a relay with a 24v coil might be more appropriate? Would the 24v relay be able to handle a higher number of amps?

Yes I did exactly this to test the relay, and it worked perfectly. Now, having used it connected to the CDU etc, its broken. Not to worry, it was only an attempt to improve reliability. I'll list the remaining items on Ebay and try and recoup my money!

Well, thank you all for your help and replies. I’m obviously at the limit of my understanding of electrical stuffs, so I’ll retire gracefully and put the idea of latching relays for changing frog polarity to bed. 12v latching relays now available on EBay!

I wasn’t sure how to measure the output of the cdu, as it’s momentarily on, I couldn’t get an accurate reading with my multimeter. Is there a way to measure it? Edit, I have measured across the terminal. 23.4v… there’s my answer confirmed… if only I figured this out before hand. Doh! Even the 24v relays have a max set/reset voltage of 19.2….

Yes they do. In short, I think the CDU has supplied too much voltage and blown the relay. The CDU outputs DC voltage. It is this exact model: https://www.layouts4u.net/other-products/track-related-items/block-signalling-cdu1c When testing the other relays with 12v DC, there is an audible click, and you can feel it inside the relay, and the output changes as you'd expect. I'd imagine 24v relays would work well, I just don't want to spend another £24! Oh well, live and learn. The relays have 10 pins, and testing on the bench has shown them to work exactly as advertised, so I am confident I have the right type, just the wrong coil voltage.

Its these ones Jeremy: https://www.rapidonline.com/Catalogue/Search?Query=Hongfa HFD2%2F012-S-L2-D PCB Signal Relay 12VDC DPDT 2A&Size=20 What concerns me is that the relay switched 'on the bench' with a 9v battery, and now, the same relay won't switch under the same conditions with a 9v supply. I'm just charging up a 12v power supply, to see if that works....

How do you mean? My limited understanding is that the power to move the solenoid comes from the switch via the CDU, and the solenoid requires the power of the CDU in order to move it. How would the relay be switched in this instance? They are Hongfa 12v Relays, the power to the CDU is 16v AC and the output from the CDU is whatever it is, as I couldn't measure it as the power is too momentary. I'm guessing there are too many volts going through it, and I've blown the relay!

Well done that man! 12 11 Latching relays now available on Ebay...

Well, I said I'd report back. Got my 12 Latching Relays from Rapid Online, and they certainly were Rapid. Ordered at 5pm, came the next day at 9am! Excellent! Tested a 12v relay with a 9v battery. Heard the little click. Relay works, so far so good. Get the multi meter out test the output, and yes its working as advertised. Continuity switches between +ve and -ve. Remove the power and there's no continuity at all. Ok good that seems to make sense, if the relay isn't powered, the little electro magnet inside or whatever isn't making a circuit. Wire one into the layout feeling happy that I may have found the solution. Gingerly apply power, and the point works flawlessly in the straight on configuration. Throw the point. Apply power. Nothing. Test the relay. No click. Remove and test again. Nothing. Test with multi meter. Circuit is permanently open one way and won't switch back. I'm assuming too much voltage has come through the relay and welded it to one side, either way, its buggered! Really not sure what to do about this. I have a CDU supplying the point motor, I chose 12v latching relays assuming the voltage would be low. Without spending another £24 on another set of 24v relays, it seems my dream of perfect point polarity switching on the cheap is over.

I can see that would work well Keith. Nice and simple!