Wiring accessories to constant voltage

Mike:

Not sure what you are asking wrt 2 wire accessory. To me a 2 wire accessory is like a light bulb (IE power and common wires). It is either on or off usually by way of a switch inline with the power wire. I assume you can connect the accessory com to an isolated portion of your track and let a train's truck complete the circuit. You could even use an independent accessory transformer as long as its common and the track common are tied together. This makes the isolated track the 'switch'. However I was always told that the common should always be connected and a switch placed on the power line. When a device is turned on then off it always has a residual voltage left that must be dissipated through the common line to ground. If you use the common to turn the device on/off it can not dissipate the excess voltage so this voltage is added to the to the next voltage cycle at turn on. Eventually there is more voltage at turn on then the device can handle and it burns out.

Joe

To me a two wire accessory is a crossing gate, or a banjo signal.  No including street lights because they don't need to be connected to the track.  a three wire accessory to me is one with probably a light that is connected to a constant (somehow) such as the news stand or the gateman or the 192 tower.

Your "fixation" on the KW is likely the problem - there are only two fixed voltages on the KW - 6 volts and 20 volts relative to the common "U" posts.   2 wire vs. 3 wire is not the issue, so yes, if you try to use "C" or "D" as common on an insulated rail activated accessory with a KW, you will encounter a short, either 6 volts or 20 volts, and lots of amps, but that is the limitation of the transformer, not the wiring scheme.

If you run trains with "A" and use "B" as an adjustable "constant voltage" source, then you now have three available voltage taps for accessories... 6v, 20v, & adjustable. The KW just isn't accessory-friendly.

The KW is what I use and you're right, it's got 6, 14 and 20 volts but nothing I have uses 6 or 20 volts. 

So how do you get something like the banjo off the track power/variable voltage and onto constant so it activates at a constant 14V when the train passes.    use a contactor because it is not using power from the track?  or can't be done.

I use multiple transformers for my layout.  No ZW or KW's due to space limitations.

One transformer for track power, one for AC Accessories, one for DC accessories, one for lights and one for constant power to Turnouts.

Why not just add a small transformer to your layout to power your 2 wire or three wire accessories?

@Mike23 posted:

The KW is what I use and you're right, it's got 6, 14 and 20 volts ...

The 14 volts on the KW is only for non-insulated track-tripped accessories - lights, loaders, etc, that have no need to reference common.

@Mike23 posted:

So how do you get something like the banjo off the track power/variable voltage and onto constant so it activates at a constant 14V when the train passes.    use a contactor because it is not using power from the track?  or can't be done.

It can be done with a voltage dropping diode array on the 20 volt post.

There is a lot of reading on this subject HERE.

ok disregarding the voltage dropping diodes- I can't seem to get past the "fact?" that accessories like the banjo, news stand or crossing gate, that activate only when the train passes (wheels touching the rail) can't be hooked up to the constant posts. And that's because when the wheels make the connection, it gives the accessory whatever power the track is on. - Is that correct?

Now, I have three separate loops running on two completely separate transformers. There are accessories on all three loops. At the transformer this leaves one unused throttle. Can I use this throttle pre-set to 14 volts to run ALL accessories on all three loops OR do I now need to connect the transformers in phase or parallel.

Thanks for sticking with this thread. Here's a video for your help!

@Mike23 posted:

I can't seem to get past the "fact?" that accessories like the banjo, news stand or crossing gate, that activate only when the train passes (wheels touching the rail) can't be hooked up to the constant posts.

This is NOT a fact, it is fiction.

@Mike23 posted:

And that's because when the wheels make the connection, it gives the accessory whatever power the track is on. - Is that correct?

Incorrect.

You can use the insulated trigger rail to switch any power you desire to an accessory, even DC or a car battery, or 120v AC(not recommended!). All you need to realize is that the wheels/axle set are like a knife switch or toggle switch, completing a circuit from one running rail to the other insulated rail. The fact that we exploit the common on a train layout is for convenience, and the voltage potential between the center rail and the outside rails that the train runs on is irrelevant to the accessory operation.

I see the picture now. You are completely right, the contactor is separate from the track and is hooked to constant posts. Sorry I wasn't clear on my questions.     I don't want to use the contactors. They're to bulky. I had thought and hoped that I could solder wires directly to the rails and in conjunction with an isolated rail, connect to constant...However that is not true, at least not without some fancy wiring stuff.   

Looks like I'll use a extra, little transformer set at a constant voltage and a bunch of 153 contactors or such.

Although I'm using 2 transformers to run 3 completely separate loops. that leaves one throttle (the 4th) free. Can I use that to control ALL accessories on all 3 loops...or do I now need transformers in phase or something

Here is a good tutorial on phasing. Although it's not always necessary, it does keep order on a layout.

@Mike23 posted:

... I had thought and hoped that I could solder wires directly to the rails and in conjunction with an isolated rail, connect to constant...However that is not true, at least not without some fancy wiring stuff.

Mike, it is trueif you follow the diagram above for your KW transformer using the "B" post. This will work perfectly as you desire. In the alternative, you can use the exact same diagram, substituting a separate transformer for the KW B & U posts.

I’m missing something.

The B post is variable. And nothing is connected to constant. So how is that constant?  . That’s track power. Using a contactor clip, it connects to a constant post.
 

@Mike23 posted:

I’m missing something.

Yes, on the KW it's only "track power" if you are using it for running a train, look at the instructions. Otherwise, it is literally the same as the A. C, & D posts as they all tap into the same transformer secondary, two fixed(6v & 20v) & two variable(6-20v & 6-20v) as reference to common "U", and the output is shared among all. Like the new(~20 years now) CW-80, the B post can also be used as a programmable constant voltage post(or train power for a trolley or motorized unit). The instructions for the KW & ZW suggest a setting of "12-14 volts" for accessory usage, leaving it at that setting makes it "constant".

Thank you all for the help!