dcc and remote control turnouts

[rile42]

Today I thought I'd try to wire up one of the many turnouts on my experimental layout that I'm using to familiarize myself with the aspects of dcc operations.  My system is powered by a Digitrax Zephyr controller.  Apparantley I'm not as familiar as I thought.
I connected the switch control and the side turnout motor correctly.  To power the switch control, I ran feeds to the bus wire powering the track.  The turnout didn't work.  Thinking it might have had a bad motor, I wired to another switch, it didn't work.  I checked power with a multimeter and power was getting to the turnouts.
Finally, I took an old dc controller I had, connected the switch control to the AC outlet on it and the turnouts worked.
My guess, and please tell me if I'm incorrect is that there was not enough power from the bus wire to run the turnouts.  I measured the power, based on the Digitrax instructions on measuring track voltage and got 6.9 volts on one track and 6.5 volts on the other which according to Digitrax means a track voltage of 13.4 volts.  I'm assuming, and I know that is disasterous, that the same voltage is probably cruising through the bus wire.  Maybe none of that measuring means anything in powering the turnout but I thought it would explain what I did.
I had hoped that I could power the switches using the Digitrax without an added power supply.
Am I doing something wrong? 

[Doneldon]

rile-

Not exactly wrong, but possibly problematic. You can control DCC turnouts with DCC track power. Non-DCC turnouts need their own power supply, something on the order of 10-14 volts AC or DC, and an amp or so. (Some say DC is better.) Any old power pack, transformer or wall wart from a cell phone or other electrical device with the correct output will work. If you plan to gang turnouts so you can set routes with one control (like for entering or exiting a yard), you should consider a capacitive discharge circuit which can send enough power to throw all of the switches but instantly break contact so you don't burn out the delicate little solenoids in the switch machines.

Also, don't rely on a conventional volt-ohm meter to give you information about the electrical contents of DCC track.
                                                                                                                                                                           -- D

[Jim Banner]

If you really, really want to run regular turnouts off DCC, you can do it using a bridge rectifier to turn the high frequency ac into dc.  Then you need a resistor to limit the current drawn from your DCC system (50 to 100 ohms or so) and a large capacitor to store enough energy to throw the switch (4700 to 10,000 microfarads at 25 volts.)  Some readers may recognize this as a basic capacitor discharge circuit, which is great for throwing switches.

DCC straight from your system is relatively high frequency.  This means it does not flow through coils as easily as dc and low frequency ac.  This in turn means that the coils in dual solenoid switch machines do not get enough current to operate properly.  By turning the high frequency ac into dc, the coils get enough current to operate.  But remember that the above circuit draws about as much current as a locomotive.  Depending on your DCC system, you may or may not want to decrease the maximum number of locomotives you can run at once.

The economics of this approach are questionable.  The parts listed above cost about $5, not including a box to mount them all in.  A wall wart power supply rated 12 to 15 volts, 1 or more amps, can often be had at thrift stores for a couple of dollars.  And a used model railroad power pack can often be found for $10 or less - much less if the dc output does not work but the ac output does.

So there you have it - the whys and why nots of running standard turnouts off DCC.

Jim