stan2004 posted:JTrains posted:...The situation is certainly not a show-stopper by any means, so I'd probably say converting to DC switch operation and having localized filtering is hunting flies with a bazooka. I might end up doing a test with the DC boost to see if it makes any real difference - else, it will just remain one of those charms of PW Lionel layouts.Well, this being a discussion forum, some additional thoughts. I think DC is the way to go. I also appreciate the idea that fussing with a dozen plus switches (converting to LED, adding filtering, etc.) can be a hassle. So for the sake of discussion, we can contrive a requirement that the switches themselves are not to be modified.
One tricky part about staying AC is how to sense the momentary solenoid current surge in a timely manner. AC sensors typically average the voltage or current over many 60 Hz line-cycles to get an accurate reading. As you know, a switch solenoid can do its thing in a fraction of a second. So without timely sensing of the solenoid current, the boost circuit could be late to apply the boost, and late to remove the boost. I suppose you can forego averaging and instantaneously apply the boost whenever the current exceeds +2 Amps (some threshold above the peak of the 1 Amp peak steady-state current). Then the trick becomes the circuit that swaps in the boost voltage 60 times a second - probably want to go solid-state vs. a chattering electro-mechanical relay.
Obviously, sensing the solenoid current increase (and decrease) in a DC configuration can be instantaneous - no delay "waiting" for the voltage or current to cycle. Plus, it stands to reason that inserting a DC boost is "easier" if adding to a steady-state DC than to a steady-state AC. Again, while an electro-mechanical relay might be fast enough, it can never be as fast to pick-up and release as a transistor/solid-state switch. And transistors really appreciate working in an all DC environment!
Another idea easier to implement in DC is remote-sensing - a standard power-supply regulation method. Since all your switches apparently see the same voltage drop, you can monitor the voltage way out at a switch and feed back to the control circuit near the transformer. As a sense wire, this would carry negligible current so thin wire is fine. The controller circuit would boost the voltage at the transformer to maintain a constant voltage (e.g., 13V DC) at the switch irrespective of solenoid activity.
A possible gotcha with DC operation is where you are getting the DC in the first place. If deriving from AC accessory voltage thru a bridge-rectifier, this would make the DC- "ground" voltage different from the AC common. This may have implications if using anti-derail operation. Of course you can get inexpensive DC supplies (e.g. a 90 Watt DC-output laptop charger for $10) that would be an isolated source so can share DC "ground" with AC common but does add to the wiring jungle!
Discussions are indeed good. Let’s continue with this a bit more.
When I said “switch in” a DC boost, my thinking was literally to switch it in: my control panel is built with DPDTs with the second pole unused. So my thought was to wire up the second pole with a static DC boost of a couple of volts and when the switch was physically actuated to bridge that over into circuit. This would mechanically remove the sensing part of the equation and keep all of the complexity back at the switch panel. Your point that the DC source has to be beefy is a good one, as it would need to provide sufficient near-instantaneous power which itself could present challenge else it was all for naught. Sounds like a job for some filter supercaps!
However, over my first cup of coffee…
…your comments got me thinking: how do we normally increase the power of a weak AC signal? Looking down next to my bench at one of my other projects (a Fender-ish F51 FrankenChamp), it occurred to me: an amplifier! Feed in the steady-state AC voltage, amplify the voltage and do a bit of transformer magic, make sure the output is in phase, and voila. Need to think this through a bit more – but talk about overkill! Did I mention that the 5F1 is a vacuum tube amp? Adding some superfluous NIXIE tubes would complete the paradigm, methinks - and give me some hipster/steampunk cred at the same time.
