I’m putting together a DC HO layout using Atlas #56 Switch controls and a Microminiatures Points Indicator for my board, as it’s a ceiling train layout & I can’t visually check the turnouts at all times.
I’m running everything with an MRC Tech 4 transformer.
The points indicator is very specific as to input polarity but it seems that neither the transformer nor the switch controllers are that concerned about it. I can determine the polarity on the AC terminals of the transformer with a multimeter (as there’s no polarity markings on it either) but short of ripping apart an extra switch controller, there’s no way to tell what input should go where. I even contacted Atlas about it but all they sent me back was a scan of the back of the package that says ‘attach leads from transformer here’. Hooking up the outputs I understand.
Any suggestions?
PS - Microminiatures wasn’t any more helpful as they seemed surprised that I should ask about what the wattage should be for the 12V DC power input…
Your switch machines can be run from AC or DC. It sounds as though you are using AC - AC has no polarity, and can be wired either way. In this case (for switch machines) even DC power isn’t polarity sensitive for hooking them up.
On the points indicator board, the diagram only shows polarity sensitivity on the points indicator power supply. That needs to be a DC power source because it powers the LEDs and they require DC to function properly. A simple 12 volt wall-pack would be adequate for powering the LEDs.
Not meaning to beat a dead horse here, Mark - and thanks for the advice! - but we’ve all been educated about the big prongs on plugs for other things running on AC so I guess you can see where I got the idea that it was important.
The big prong on a AC plug is to make sure the equipment being plugged into the wall outlet is in phase with the Black wire witch is attached to your cicuit breakers in your wall panel in your house and the other prong goes to the neutral wire White in your buss bar in your wall panel in your house, which is also attached to your ground, before the added ground, green wire. It protects the equipment also being used from surges and power outages to be in Phase. Hence 60 cycles,being in phase.
OK; here’s what’s throwing me: on this wiring diagram, it appears that there has to be a lead coming off the AC power input to the points motors which then goes into the COM of the indicator board. Is this right?
Yes, that is correct. You can just connect a wire from the center connection of one of the switch controller outputs to the COM of the indicator board.
I see no concern about polarity, jus that you need to keep one side of the AC as common to ALL switch motors, which is autiomatically handled if you use the Atlas control boxes. If you have multiple groups of the Atlas control boxes, just make sure the same side of the AC is conencted to the top terminal on the side and the same side is conencted to the bottom terminal of all groups. Normally they all get daisy chained to one another with the screws and tabs and there is only one pair of wires feeding AC to the whole gang of control boxes. It’s important to keep that straight otherwise it could fry the input on the switch position reporting board.
The polarity on the LED side also matters, LEDs only work when wired with the correct polarity. But mess that up and all that will happen is the LED that’s wired backwards won’t light up.
The Atlas switch motors are basically two small coils. with a movable steel core. They will operate on AC or DC. When you activate the switch motor momentarily, power is applied to one or the other coil, moving the steel rod one way or the other.
Thanks, Hobo, I do understand how momentary pulse switches work, which is why I’m using a points indicator. And Mark, I did mention in my preamble that I was using a train transformer for accessory power for those Atlas switches. But thanks for your concern. I think I’ve ‘got it’, now - thanks to all!
Take note of the “CDU if fitted” box in your diagram. A CDU, or Capacitive Discharge Unit, stores energy until it is needed, and then hits the coil with a much stronger pulse than you will get from the power supply alone. Then, it limits the current that can flow through the coil while it is still energized. A CDU is particularly worthwhile for your situation, so please consider adding one.
First, your ceiling layout will have long wire runs from the panel to the turnouts. This means voltage loss along the wires, reducing available power to the coils. The CDU provides the extra power needed to overcome this.
Second, those Atlas pushbutton controllers have a reputation, which from personal experience is well-deserved, of sticking in the ON position. This sends continuous power to the coil, which will burn it out in only a few minutes. The CDU limits the current after the initial kick, and will thus protect your turnouts in case of a sticky-button incident.
Thanks for all that great info based on the reality of my situation! I had been considering a CDU; I guess I can now also admit we’re talking about Bachmann EZ track turnouts, here…so yeah, every little bit can only help…
Do you not have the controlers that come with them? If they did, and they are the newer ones(a good bit thicker than the Atlas ones or the older Bachmann ones), then they actually have a capacitor discharge circuit built in.
So if I used the EZ track controllers, another CDU would be unnecessary, and even hazardous, from what I’ve been reading. But I’m not sure I’ve got them all. I don’t mind going the route of adding a CDU to an Atlas spread; but I don’t know how big of one I should get. The farthest turnout is about 19 feet away from the comtrol board, with the other 5 in lesser distance but all with a minimum of 10 feet.
I’ve been looking at a couple of possibilities - Micro Miniatures in the UK makes a 4700uf one for about $25; and I’ve seen that there’s a Peco one also available but I can’t find any specs for it. And there’s another company called 2K Technologies that has a 70V 4400 uf with a diode to prevent back emf…
Circuitron has the Snapper which is a good one as well. And Rob Paisley’s Electronics site has circuit digrams for them, they are dead simple to build, usually just 1 diode, 1 transistor, 1 or 2 resistors, and the capacitor. Just pay attention to the polarity markings on components that are polarized (diode, transistor, adn capacitor) and it’s super easy to just build one.
