@Rod Stewart posted:The addition of say a 100uf filter cap would damp out any relay chatter, and it could likely fit just between the two terminal blocks on your minimalist perf board Stan. But then we've added 50 % more components and probably 25 cents in cost. And assuming a 12vac supply, the coil voltage will be up around 16 vdc, which might be a bit much? What's the max voltage rating for that coil?
To be clear, I think we are dealing with 2 types of relay chatter in the context of O-gauge train operation with AC voltages.
1) 60 Hz chatter where many of these small relays are mechanically "fast enough" to rapidly move its contacts thereby buzzing 60 times per second (if half-wave rectified with a single diode like your design) or even 120 times per second (if full-wave rectified with a bridge rectifier). A 100uF capacitor would certainly provide an adequate reservoir of stored energy to remove the line frequency chatter. Some techno-geeky back-of-envelope calculation that I don't know the answer to as I type this so let's see if I make a fool of myself:
While the nominal coil power of this relay is 0.2 Watts, we know (once closed) it will stay closed if you provide as little as about 0.002 Watts (1.2V x 2mA) which is pretty remarkable when you think about it! We'd need that power level for, at most, 1 60 Hz line-cycle for half-wave operation and possibly even a chopped-sine transformer with pulse-like AC. Let's just call it 20 millisec. 0.002 Watts for 20 millisec = 40 microJoules. Bear with me. A 100uF capacitor charged up to 16V DC stores about 10 milliJoules of energy...or 250 times more than required to deal with line-frequency chatter! I was doing the math as I typed so maybe I'm off a bit but this sounds about right.
2) The other relay chatter is from intermittent wheel-to-track contact in insulated-rail triggering. You need much more capacitor energy to mask this type of chatter. Let's just say you want to mask drop-outs of 100 millisec or 1/10th second which seems a ballpark duration for flickering signal bulbs I've seen. So that's about 50 times longer than the line-frequency chatter but a 100uF still stores adequate reserve power for that task too!
Again, the Dollar Tree version (NO capacitor) has no hope of guarding against the 2nd type of relay chatter! This version is narrowly focused on the dual/multiple 153IR signaling application where you don't have the insulated-rail wheel chatter.
Separately, you ask about the coil voltage if a capacitor were placed in the Dollar Tree version. If it charges up to 16V, that would indeed push the 15.6V spec'd max voltage. So, yup, that would be a case where a resistor or whatever to limit coil power would be a good idea.
